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                    ROSKOP DAIRY v. GEA FARM TECH.
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             Roskop Dairy, L.L.C., appellant, v. GEA
              Farm Technologies, Inc., and Midwest
                Livestock Systems, Inc., appellees.
                               ___ N.W.2d ___

                    Filed December 4, 2015.   No. S-14-115.

 1.	 Trial: Expert Witnesses: Appeal and Error. An appellate court reviews
     de novo whether the trial court applied the correct legal standards for
     admitting an expert’s testimony.
 2.	 ____: ____: ____. An appellate court reviews for abuse of discretion
     how the trial court applied the appropriate standards in deciding whether
     to admit or exclude an expert’s testimony.
 3.	 Summary Judgment: Appeal and Error. In reviewing a summary
     judgment, an appellate court views the evidence in the light most
     favorable to the party against whom the judgment was granted and
     gives that party the benefit of all reasonable inferences deducible from
     the evidence.
 4.	 Evidence: Appeal and Error. Generally, the control of discovery is a
     matter for judicial discretion, and decisions regarding discovery will be
     upheld on appeal in the absence of an abuse of discretion.
 5.	 Prejudgment Interest: Appeal and Error. Prejudgment interest may
     be awarded only as provided in Neb. Rev. Stat. § 45-103.02 (Reissue
     2010), and whether prejudgment interest should be awarded is reviewed
     de novo on appeal.
 6.	 Summary Judgment. A motion for summary judgment shall be granted
     where there is no genuine issue as to any material fact and the moving
     party is entitled to judgment as a matter of law.
 7.	 Evidence: Proof. Failure of proof concerning an essential element of the
     nonmoving party’s case necessarily renders all other facts immaterial.
 8.	 Summary Judgment: Proof. A party moving for summary judgment
     makes a prima facie case for summary judgment by producing enough
     evidence to demonstrate that the movant is entitled to judgment if the
     evidence were uncontroverted at trial.
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                        Nebraska A dvance Sheets
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                     ROSKOP DAIRY v. GEA FARM TECH.
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  9.	 ____: ____. Once the moving party makes a prima facie case, the bur-
      den shifts to the party opposing the motion to produce admissible con-
      tradictory evidence showing the existence of a material issue of fact that
      prevents judgment as a matter of law.
10.	 Summary Judgment: Evidence. Conclusions based on guess, specula-
      tion, conjecture, or a choice of possibilities do not create material issues
      of fact for the purposes of summary judgment; the evidence must be
      sufficient to support an inference in the nonmovant’s favor without the
      fact finder engaging in guesswork.
11.	 Products Liability: Warranty. All implied warranty theories of recov-
      ery and strict liability claims for manufacturing defect, design defect, or
      failure to warn seek to recover for a “defect.”
12.	 Actions: Negligence: Warranty: Proximate Cause. Whether a plaintiff
      is proceeding under negligence, defect theories, or breach of express
      warranty, proximate cause is a necessary element of the plaintiff’s case.
13.	 Negligence: Proximate Cause: Words and Phrases. Proximate cause
      is the cause that in a natural and continuous sequence unbroken by an
      efficient intervening cause, produces the injury, and without which the
      injury would not have occurred.
14.	 Negligence: Proximate Cause: Proof. To establish proximate cause, the
      plaintiff must meet three basic requirements: (1) Without the negligent
      action, the injury would not have occurred, commonly known as the
      “but for” rule or “cause in fact”; (2) the injury was a natural and prob-
      able result of the negligence; and (3) there was no efficient interven-
      ing cause.
15.	 Expert Witnesses: Testimony. Findings of fact as to technical matters
      beyond the scope of ordinary experience are usually not warranted in the
      absence of expert testimony supporting such findings.
16.	 Testimony. It is well settled that a causation opinion based solely on a
      temporal relationship is not derived from the scientific method and is
      therefore unreliable.
17.	 Products Liability: Proof. Under the malfunction theory, also some-
      times called the indeterminate defect theory or general defect theory, a
      plaintiff may prove a product defect circumstantially, without proof of
      a specific defect, when (1) the incident causing the harm was of a kind
      that would ordinarily occur only as a result of a product defect and (2)
      the incident was not, in the particular case, solely the result of causes
      other than a product defect existing at the time of sale or distribution.
18.	 Circumstantial Evidence: Verdicts. Circumstantial evidence is not
      sufficient to sustain a verdict that depends solely thereon unless the cir-
      cumstances proved by the evidence are of such a nature and so related
      to each other that the conclusion reached by the jury is the only one that
      can fairly and reasonably be drawn therefrom.
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                    ROSKOP DAIRY v. GEA FARM TECH.
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19.	 Juries: Evidence. Where, under the facts viewed in a light most favor-
     able to the nonmoving party, the nonexistence of the fact to be inferred
     is just as probable as its existence, the conclusion that it exists is a
     matter of speculation, surmise, and conjecture, and a jury will not be
     permitted to draw it.
20.	 Evidence. The line between impermissible speculation and reasonable
     inferences is drawn by the laws of logic.
21.	 ____. Reasoning causation from temporal correlation represents a logi-
     cal fallacy. A conclusion based upon such reasoning is not a reasonable
     inference but is mere speculation and conjecture.
22.	 Rules of the Supreme Court: Appeal and Error. It is incumbent
     upon the party appealing to present a record which supports the errors
     assigned. Neb. Rev. Stat. § 25-1140 (Reissue 2008) and Neb. Ct. R.
     App. P. § 2-105(B)(1)(b) (rev. 2010) place the burden on the appel-
     lant to file a praecipe identifying the matter to be contained in the bill
     of exceptions.
23.	 Prejudgment Interest: Claims. A claim is liquidated for purposes of
     prejudgment interest when there is no reasonable controversy as to both
     the amount due and the plaintiff’s right to recover.

  Appeal from the District Court for Gage County: Paul W.
Korslund, Judge. Affirmed in part, and in part reversed.
   Kristopher J. Covi, of McGrath, North, Mullin & Kratz,
P.C., L.L.O., for appellant.
  Stephen L. Ahl and Nathan D. Anderson, of Wolfe, Snowden,
Hurd, Luers & Ahl, L.L.P., for appellee Midwest Livestock
Systems, Inc.
  William M. Bremer and Ann M. Byrne, of Bremer & Nelson,
L.L.P., and Catherine L. Stegman and Joseph S. Daly, of
Sorodo, Daly, Shomaker & Selde, P.C., L.L.O., for appellee
GEA Farm Technologies, Inc.
  Connolly, Stephan, McCormack, Miller-Lerman, and
Cassel, JJ.
   McCormack, J.
                     NATURE OF CASE
   A dairy appeals from the district court’s order of summary
judgment in favor of a manufacturer of a microprocessor-based
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milking control unit and the dealer of that unit (collectively the
defendants). The principal issue is whether the dairy rebutted
the defendants’ prima facie case that mechanical components
of the milking system maintained by the dairy and not a part
of the microprocessor-based control unit were the proximate
cause of the alleged damages.
                        BACKGROUND
   Roskop Dairy, L.L.C. (Roskop Dairy), owned by Michael
Roskop (Roskop), is a commercial dairy operation. GEA Farm
Technologies, Inc. (GEA), manufactures automated dairy
equipment used in dairy systems. Midwest Livestock Systems,
Inc. (Midwest), was an authorized dealer of GEA products.
   Roskop Dairy sued the defendants for damages allegedly
stemming from the “Dematron 60 Air Detacher Package”
(Dematron) manufactured by GEA and purchased by Roskop
Dairy from Midwest. The total purchase price was $153,027.88.
Roskop Dairy paid Midwest a downpayment of $33,600 and
made a second payment of $70,000. Roskop Dairy never paid
the remainder.
   The installation of the Dematron at Roskop Dairy occurred
in June 2008. There was no evidence of a service agreement
by which Midwest was to regularly inspect or maintain other
component parts of Roskop Dairy’s milking system that were
not provided by Midwest.
   Roskop Dairy sued the defendants for breach of express and
implied warranties and negligence. Roskop Dairy theorized
that Midwest negligently and defectively installed and pro-
grammed the Dematron. Specifically, Roskop Dairy asserted
that improper parameter settings caused the milking units to
detach while still under significant vacuum and thereby harmed
the teats of the dairy cows, resulting in mastitis and lowered
milk production. Roskop Dairy did not allege liability based on
negligent maintenance of the physical component parts of the
milking system that are not part of the Dematron.
   The defendants generally denied liability and asserted that
Roskop Dairy’s contributory negligence barred any claim
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against them. Midwest counterclaimed for the principal amount
still due under the sales contract agreement, as well as for 8
percent interest per annum from the payment due date. After
discovery, the defendants moved for summary judgment.
                  Milking System, Dematron,
                   and Somatic Cell Counts
   Roskop Dairy has 50 milking “parlors” used to milk approx-
imately 700 cows. When a cow enters a parlor, an employee of
Roskop Dairy manually prepares the cow’s teats by cleaning
them and stimulating let down. The employee then presses a
button to apply vacuum to the milking “claw.” The employee
applies the claw to the teats, and milking begins. Milk flows
through tubes into holding tanks. The claw, vacuum, tubes, and
tanks are not part of the Dematron.
   The Dematron is a microprocessor-based milking control
unit that monitors signals from milking sensors in the milk-
ing system and sends signals to that system to control when
various processes take place after manual application of the
claw. There are multiple parameter settings involved in the
functioning of the Dematron. These settings are preset at the
factory, but are regularly adjusted to accommodate dairy own-
ers’ preferences.
   The “milk flow threshold” level is an adjustable Dematron
parameter that indicates when the system should finish milk-
ing. Another Dematron parameter, “blink time,” is the length
of time a cow must be below the milk flow threshold before
detachment of the claw will start. A component in the sys-
tem actually blinks during the blink time, and milk flow can
also be observed through clear lenses attached to the top of
the claw. After the cow is below the milk flow threshold for
the desired blink time, the Dematron shuts off the vacuum
by sending a signal to a “shifting valve” that is also part of
the Dematron.
   After the vacuum is shut off, it should quickly dissipate.
Depending on the model of claw, vacuum dissipates either
through vents in the metal claw itself or in clear plastic
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replaceable lenses that attach to the top of the claws. In the
model of claw used at Roskop Dairy, the vents were located in
the lenses and not in the claw itself.
   The “detach delay” is a setting of the Dematron that controls
the time between when the vacuum is shut off and the claw is
retracted by the automated system. Retraction ideally occurs
when most, but not completely all, of the residual vacuum has
dissipated through the vents. If no residual vacuum is left when
the claw retracts, the claw will fall, rather than be retracted,
and will land on the parlor deck.
   The “milk sweep delay” is a Dematron setting controlling
the time between when the claw is retracted and when the
“milk sweep begins.” The “milk sweep” is an optional setting
and consists of a short burst of vacuum to pull any residual
milk into the tubes of the milking system.
   After detachment, the cows’ udders are manually dried with
a cloth by Roskop Dairy employees.
   The somatic cell count of the milk at a dairy is an indica-
tor of the number of mastitis organisms in the herd. Increased
somatic cell count can mean either many cows with a lesser
degree of infection or fewer cows with a worse infection.
Somatic cell counts above 400,000 are “concerning.” Below
200,000 represents a well-managed herd.
   While the somatic cell count in Roskop Dairy’s herd had
previously been in the 200,000 range, in January 2008, before
the installation of the Dematron, it significantly increased to
409,000, from 285,000 the previous month. The somatic cell
count continued in the 409,000 to 476,000 range until June
2008, when it reached 510,000.
   In July 2008, after installation of the Dematron, the somatic
cell count rose to 627,000. It went back down to 493,000 in
August, after Dematron employees visited Roskop Dairy. It is
undisputed that during that visit, Dematron employees adjusted
some parameter settings of the Dematron.
   Roskop Dairy claims that the rise in somatic cell counts in
the herd after installation of the Dematron corresponded to
a reduction in milk production that had not occurred during
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the pre-Dematron rise in somatic cell counts. Roskop did not
address the extent to which any changes in milking practices
entered into this conclusion. Roskop had milked his cows
three times a day until July 2, 2008. Since July 2, however,
he has milked his cows twice a day. Milking three times a
day versus twice a day would increase milk yield by 12 to
15 percent.
               Deposition of Michael Roskop and
                 K aren Cass’ M astitis R eports
    Roskop’s deposition was entered into evidence at the sum-
mary judgment hearing. Roskop testified that due to the timing
of events, he believed the July 2008 increase in the somatic
cell count was caused by the parameters of the Dematron’s
being set incorrectly the previous month. Roskop admitted that
he was not an expert on milking machines. He admittedly did
not fully understand the Dematron settings. But he stated that
approximately 20 days after the system was installed, his herd
experienced an increase in mastitis.
    Roskop suspected, first, that from the time the system was
installed until July 31, 2008, when Midwest employees made
further adjustments to the Dematron’s parameter settings, the
blink time was set too short, such that the machines were
detaching before the cows were fully milked. He believed this
based on the appearance of the cow udders and the fact that the
cows were not producing as much milk as he expected.
    Roskop admitted the blink time setting did not lead to mas-
titis, however. Roskop testified that his employees manually
reattached the system when the cows’ udders appeared to not
be completely milked out. Roskop did not specifically recall
which of the original blink time settings and adjustments may
have been made at his request.
    Roskop suspected that incorrect parameters for the sweep
time led to the increase in mastitis. Roskop believed that
from the time of installation until adjustments were made
on July 31, 2008, incorrect sweep time settings resulted in
the machine’s detaching while still under a vacuum. This, in
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turn, tugged on the cows’ teats, causing physical injury that
made them more susceptible to mastitis. Since discovery,
Roskop Dairy no longer asserts that the sweep time settings
led to mastitis.
   Roskop testified that from late June 2008 when the system
was installed until Midwest employees made adjustments to
the parameter settings in late July, he witnessed the claw units
being “jerked off” the cows with a lot of “tugging.” He testi-
fied that the units were coming off under vacuum and that
vacuum lasted for approximately 3 seconds before it dissipated.
Roskop did not clearly explain whether he could determine
that this vacuum was active vacuum versus residual vacuum.
At one point, he affirmed that he could hear the hissing of air
being sucked into the machine for about 3 seconds, but that at
another point, he affirmed this was the failure of the vacuum to
dissipate for approximately 3 seconds.
   During the time period that the units were detaching under
vacuum, Roskop observed approximately one-third of his
dairy cows with “everted” teat ends. Roskop explained that
normally only about 2 percent of his cows demonstrated
everted teat ends. Roskop further observed bruised teats dur-
ing that time.
   Roskop testified that he had concluded the Dematron was
in some manner the cause of the detachment under vacuum
because “when they made the change off of the sweep time,
that’s when we had the instant change of no more damage to
the teat end on the cows.” Roskop explained that although the
cows with damaged teat ends took some time to heal, new
cases of teat-end damage significantly decreased after Midwest
employees changed the parameter settings of the Dematron in
late July.
   Roskop confirmed that Roskop Dairy employees were sup-
posed to check the lenses of the claws constantly to make sure
the vents, through which the residual vacuum escapes, were
not clogged. The most common cause of vent clogging was
manure. His employees were supposed to unclog the vents if
they observed them clogged. Roskop did not specify to what
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extent his employees were successfully carrying out these
duties in the summer of 2008. Roskop indicated that sometime
in June 2008, four Roskop Dairy employees quit, because cows
were kicking them. Roskop testified that it took approximately
2 months to replace those employees.
   Roskop testified that he hired Karen Cass, a mastitis con-
sultant, to “come in and give me an outside look and test the
herd.” She observed the dairy and tested the cows on July 19,
2008. Roskop admitted that Cass observed several behaviors
of Roskop Dairy’s employees that were concerning from the
standpoint of mastitis prevention. Roskop acknowledged that
Cass’ report found various deficiencies in his employees’ care
of the cows during the milking process. Roskop did not deny
the veracity of Cass’ observations, but hoped those deficiencies
were isolated instances.
   Cass found there were too many cows with clinical mastitis
in line being milked with nonclinical cows. Cass found that
the milk and air tubes were falling off the equipment. Cass
also saw employees “flipping towels,” meaning that they were
using the same towel to wipe off the teats of more than one
cow, and were using towels that were still damp. Cass observed
that employees were not wearing gloves during manual clean-
ing and stimulation before attaching the claw. Cass wrote that
the herd’s teat-end condition “look[ed] good.”
   Roskop blamed the incidents of cows in the line show-
ing clinical mastitis on the fact that the number of sick cows
exceeded the capacity of his hospital pen. Roskop believed that
the backflush system between each cow, in any case, prevented
cross-contamination.
        Depositions of Dennis Nissen, Gerald Farrier,
           and Jeff Hunt Concerning I nstallation
                and A djustments to Dematron
   Dennis Nissen and Gerald Farrier are Midwest employ-
ees who install and maintain equipment sold by Midwest,
including the Dematron. Nissen was the employee who pri-
marily installed the Dematron at Roskop Dairy, and Farrier
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occasionally assisted. Their depositions were entered into evi-
dence at the summary judgment hearing. Jeff Hunt, a GEA
technical specialist who the parties do not dispute qualifies
as an expert, was also deposed on two occasions, and his
depositions were entered into evidence at the summary judg-
ment hearing.
   Nissen explained that it is normal to adjust the parameter
settings for the blink time and low milk threshold according
to the dairy owner’s preferences as to how thoroughly the
cows are milked. Although Nissen believed that the factory
settings were correct given his observation of the milk flow
when he installed the Dematron at Roskop Dairy, he testified
that he acceded to Roskop’s request to have the cows milked
more thoroughly by adjusting the parameters of the blink
time and low milk threshold accordingly. Nissen testified that
before doing so, he told Roskop that these were not well-
advised changes and that the cows just needed to get used to
the new detacher.
   Nissen made followup visits on July 30 and 31, 2008, after
Roskop had complained of an increase in mastitis. At those
times, Nissen checked the vacuum settings and observed the
detachers coming off the cows after milking. He testified that
he found no problems with the Dematron. Nissen testified that
he made some “minute” parameter changes.
   Three out of the 50 milking units had plungers that were not
seating properly, and they were fixed promptly. Hunt testified
that plungers do not create enough vacuum to cause the kind
of problems reported by Roskop.
   Nissen and Farrier testified that during their visits in late
July 2008, they found numerous claws that either did not have
vented lenses in them or were placed with the vent upside
down. Of the 50 claws at Roskop Dairy, Nissen found that
half had to have the lenses replaced. Farrier assumed that
Roskop or his employees had improperly replaced the lenses.
Nissen explained that the dairy must be aware of what kind of
claws it has when ordering replacement lenses, because other
models of claws do not require vented lenses. Apparently,
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the vented lenses and unvented lenses are indistinguishable
besides the presence or absence of a vent.
   Nissen explained that lenses were not part of the detacher
system sold by Midwest, but were preexisting components that
mount to the claws. Hunt likewise testified that there is no
part of the claw system that is part of the Dematron package.
According to Nissen, Midwest was not charged with maintain-
ing the claws or the lenses. Most dairy owners, according to
Nissen, handle their own maintenance of the lenses. Farrier
similarly explained that it was not “cost conducive” for dairy
owners to have Midwest maintain their lenses. Although they
did not consider it to be part of a maintenance obligation,
Nissen and Farrier used the vented lenses that Roskop had
on hand and replaced the lenses during their visits in late
July 2008.
   Hunt visited Roskop Dairy in September 2008. He made
some “routine adjustments” to a portion of the database kept
for the parlors, but he did not make any changes affecting the
detachers. He did not observe anything out of the ordinary in
the operation of the detacher system.
   Hunt testified that the factory setting for detach delay is 0
seconds. He explained that the reason for that setting is that
vacuum detachment cylinders typically do not operate instan-
taneously. And if the detach delay is set for longer than 0
seconds, the claw will usually drop before the rope is taut and
allow the claw to fall to the deck. But detach delay, like other
settings, may be adjusted by dairy personnel and the installer
at the time of installation or first use.
   Hunt testified that based on computer records of the
Dematron settings at the time of installation, the detach delay
was originally set for 3 seconds around the time of installation.
When Nissen and Farrier visited Roskop Dairy in late July
2008, they changed the detach delay setting from 3 seconds to
10 seconds. By February 2013, however, the detach delay set-
ting had been reduced from 10 seconds to 1 second.
   Hunt explained that, generally, “[l]enses without vent holes
or claws with no venting is a cause of poor residual vacuum
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decay.” Likewise, Nissen and Farrier testified that improper
venting will cause the claws to detach while still under vac-
uum. Without proper venting, these witnesses explained, there
is no way to quickly release the residual vacuum when the
vacuum is signaled by the Dematron to be turned off.
   Hunt testified that “one of the most prominent and most
probable” reasons for residual vacuum during retraction of the
claw is vents not functioning properly. Other physical compo-
nents of the milking system, however, can also cause residual
vacuum not to dissipate, such as short air tubes or vacuum
pulsation. Those other physical components are likewise not
matters controlled by the Dematron settings or maintained by
the defendants.
   Having reviewed the records, reports, and Nissen’s depo-
sition, and taking into account other possible causes, Hunt
opined that the most likely cause for the claws to retract under
vacuum in the summer of 2008 was the condition described by
Nissen of the vents in the lenses of the claws.
                 Limited Exclusion of William
                       Wailes’ Testimony
   Roskop Dairy had designated William Wailes as an expert
witness. Wailes has a bachelor’s degree in animal science and
is a member of the National Mastitis Council. He considers
himself an expert in management systems, including treatment
protocols, in the overall operation of a dairy farm. Wailes testi-
fied that he was not an expert in milking machine equipment
and that he is not a veterinarian.
   Wailes explained that there are two forms of mastitis.
Environmental mastitis comes from organisms that are in the
cow’s environment and typically involve issues of cleanliness,
keeping the manure under control, changing the bedding, and
other sanitary conditions. Contagious mastitis does not grow
in the environment but is passed from cow to cow depend-
ing on a number of factors. Usually, contagious mastitis is
passed from infected cows to uninfected cows during milk-
ing time. Wailes confirmed that according to Cass’ report,
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both environmental and contagious mastitis was present in
Roskop’s herd in the summer of 2008. Most of the cases were
contagious mastitis.
    Wailes testified generally that there are many reasons why
a dairy herd might have an outbreak of mastitis, which have
nothing to do with the milking machine. For instance, using
bare hands rather than gloves when preparing cows for the
milking machine can increase the spread of mastitis. Using
damp cloths in the milking parlor is also not advisable, because
there are opportunities for more colonies of bacteria within the
damp cloth. Using the same towel for two different cows by
flipping it over was “unacceptable,” “[b]ecause you can cross-
contaminate two cows if you use a single towel on two differ-
ent cows.”
    Further, Wailes testified that milking clinical cows in the
same line as nonclinical cows can lead to the spread of mas-
titis. Wailes testified that a backflush system will help pre-
vent certain types of contagious mastitis from spreading when
clinical cows are in the line with nonclinical cows, but not
all. Buying infected cows from other herds could also cause
an outbreak.
    Wailes had reviewed Cass’ reports in which Cass stated that
in July 2008, she had observed Roskop’s employees failing to
use gloves and using damp towels, which they flipped for use
on multiple cows. Wailes was also aware of Cass’ observation
that cows with clinical mastitis were being milked with cows
who did not have mastitis and that other cows with mastitis
were being kept in sick pens with other cows that did not have
mastitis. Wailes acknowledged these were “unacceptable” prac-
tices that could cause the spread of contagious mastitis. Wailes
did not specifically address the causal role of these practices in
the rise of mastitis in the Roskop Dairy herd.
    Wailes explained that, physically, the “first and second lines
of defense” against mastitis are a healthy teat end, “from a
sphincter muscle skin condition,” and the keratin that is in
the teat canal. But Wailes did not otherwise elaborate on how
much more susceptible to contagious mastitis a cow with
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damaged teat ends might be. Wailes did not testify that teat-end
damage alone can cause mastitis.
    Wailes further explained that teat-end lesions are “pretty
rare” and, in normal circumstances, would only result from
teats being stepped on or similar injuries. Wailes testified that
vacuum not properly shutting off before retraction of the claw
could lead to teat-end damage. In addition, certain practices
leading to overmilking, such as prepping the cow too long
before milking or a low flow rate setting, could “possibly” lead
to teat-end damage.
    Although Cass purportedly checked teat health and found
little evidence of teat-end damage in the herd in July 2008,
Wailes relied on Roskop’s statement that 30 percent of the
cows had visible teat-end damage, which would be approxi-
mately 200 cows. Wailes considered Cass to be qualified to
evaluate teat-end health—more so than Roskop—and she was
“[v]ery diligent” in her work. But Wailes questioned the logis-
tics of Cass’ making such observations while carrying out her
primary duty of obtaining clean samples from the cows to test
for mastitis.
    Wailes testified that he did not have the factual informa-
tion he needed to make a report or a “differential diagnosis
as to the causes of the cows having mastitis at the Roskop
Dairy farm in 2008.” Wailes had not reviewed Nissen’s depo-
sition and had no knowledge of the allegedly clogged vents.
Neither did Wailes consider, in reaching his opinion, the
rise in somatic cell count from January to June 2008, before
installation of the Dematron. Wailes specifically stated that
he had not ruled out the various other possible causes of a
mastitis outbreak at Roskop Dairy that would be unrelated to
the Dematron, because he did not have the necessary records
to do so.
    Wailes did not know how long the milking system was
coming off under vacuum. Wailes did not know how many
units in the system were coming off under vacuum. Wailes
had no specific information about the hygienic practices at the
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dairy in the summer of 2008 other than Cass’ report and his
longtime relationship with Roskop Dairy.
   Wailes stated that he had generally found throughout the
years that Roskop Dairy was well maintained. When asked
whether through his discussions with Roskop he had learned
of any changes in the sanitation practices at Roskop Dairy
from May to June 2008, Wailes responded, “I think he had
protocols in place for his milking facility, his people, and so
that’s, that’s my answer, he had protocols in place.” Wailes
testified that he did not specifically review what the proto-
cols were. Wailes further testified that he was not specifically
aware of what steps were taken at Roskop Dairy to enforce
its protocols.
   Wailes summarized, “[M]y analysis is that there had to be
some event to trigger somatic cell counts to take that much of
a spike.” Citing as the factual foundation for his opinion the
documentation of a spike in the somatic cell count and his con-
versation with Roskop in which Roskop related observing the
units coming off under vacuum and the teat-end damage during
the time of that spike, Wailes concluded that the alleged dam-
age to Roskop’s herd was “consistent with” the units detaching
under vacuum.
   Wailes stated that he did not have the facts to say that units
coming off under vacuum was the “probable” cause of the
spike in mastitis. He elaborated that, based on the facts he
had, he could only say it was “possible” that detachment under
vacuum caused the spike in mastitis:
         A. It’s very possible, but my, my only backup to that
      would be that when we see a spike in somatic cell counts
      something is causing the mastitis.
         Q. And we’ve agreed it could be many things?
         A. Yes.
         Q. One of which could be something wrong with the
      detacher if indeed there was?
         A. Yes.
         Q. But a lot of other things that have nothing to do
      with the detacher?
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         A. Yes.
         Q. And we can’t rule anyone in or rule anyone out
      based on the facts we have right now?
         A. It’s a dynamic issue.
   But later, Wailes mentioned that “when you try to eliminate
events that could occur during that period of time, the one that
you can’t eliminate is the installation of new equipment that
was not working properly at the time.” Wailes further stated
at counsel’s prompting that he did not find any other cause
for the spike in mastitis and loss of production in the summer
of 2008.
   On this point, Wailes elaborated only that there was no
change in feed, that Roskop had “protocols in place,” that
Cass’ report did not necessarily mean that none of the dairy
workers were exercising good hygiene practices, and that
he had no reason to believe new cows had been introduced
into the herd. Wailes then answered affirmatively to Roskop
Dairy’s counsel’s question as to whether his “analysis that
the detacher system caused the damage [was] based in part
on the fact that [Wailes had] either eliminated or not been
provided with any evidence of any other causes during that
time frame.”
   But when Midwest’s counsel asked, “You said you didn’t
find any other cause other than the installation, but fair to
say you didn’t really look for any other cause other than the
installation; is that correct?” Wailes answered, “My main con-
cern at the time was the timing of the events, and the timing
of the events match up to the installation.” Midwest’s counsel
then pressed, “But, sir, the question I asked you was did you
look for any other causes?” Wailes answered, “No.”
   Wailes again clarified that he did not know what, if any-
thing, was wrong with the Dematron and had no opinion about
the parameter settings. Wailes stated that he was not an expert
in the design, installation, diagnosis, settings, or repair of milk-
ing machine equipment.
   Wailes confirmed generally that “a properly operat-
ing detacher system” does not “come off under pressure as
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described by . . . Roskop.” But Wailes also acknowledged
that there were many reasons other than the Dematron why
units could come off under vacuum. Wailes described these
as including improper venting of the claws, misapplication
of the unit to the udders, kinks in the hoses, and cow move-
ment. Wailes further conceded there were other parts of the
milking system that, if not properly maintained by the dairy
farmer, could cause conditions conducive to cows’ getting con-
tagious forms of mastitis. Thus, Wailes agreed that it would not
be “scientific reasoning” to conclude that the Dematron was
responsible for the claws’ detaching under vacuum.
   The defendants moved to strike Wailes’ testimony on the
issue of causation, asserting that his testimony represented
mere speculation and conjecture and was based on unscientific
methodology and insufficient facts to meet the requirements
of Schafersman v. Agland Coop.1 The district court granted
the motion and excluded Wailes’ testimony insofar as Wailes
sought to opine that the units were coming off under vacuum
because of something wrong with the Dematron or that the
increase in mastitis was caused by the units detaching under
vacuum. Wailes’ deposition was not offered at the summary
judgment hearing.

                 Limited Exclusion of Michael
                      Slattery’s Testimony
   Michael Slattery is Roskop Dairy’s veterinarian. In his
deposition, Slattery discussed in the abstract several possible
causes of an increased somatic cell count in a dairy herd. In
addition to the factors discussed by Wailes and acknowledged
by Roskop in his discussion of Cass’ report, Slattery testi-
fied that the “inflations” components of the milking machine
could be worn out and porous, therefore harboring bacteria
and leading to an increase in mastitis. He also added that
high temperatures and humidity can lead to an increase in

 1	
      Schafersman v. Agland Coop, 268 Neb. 138, 681 N.W.2d 47 (2004).
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the spread of mastitis. Finally, milking cows on manual for
too long could lead to overmilking and increased incidents
of mastitis.
   Slattery stated he believed that the increase in mastitis at
Roskop Dairy was due to the Dematron, although he did not
observe anything wrong with the Dematron and explained that
he was not an expert on milking machines. Rather, he testified
that he based his conclusion solely on Roskop’s statement that
the somatic cell count of the herd increased after the Dematron
was installed. Slattery conceded he did not look at any data
and did not eliminate the other possible causes of increased
somatic cell count that had been discussed.
   Upon the defendants’ motion in limine, the court excluded
Slattery’s testimony to the extent that it concerned the proxi-
mate causation of the increased somatic cell count at Roskop
Dairy in the summer of 2008. Slattery’s deposition was
offered by Roskop at the summary judgment hearing. It was
allowed into evidence only to the extent that it contained “fac-
tual observations.”
             Order Granting Summary Judgment
   The court granted the defendants’ motions for summary
judgment. In its order, the court noted that it had stricken the
causation testimony of both Slattery and Wailes as unreliable.
But it also noted in its order that “[b]oth Slattery and Wailes
admitted there are numerous possible causes for spikes in a
dairy herd’s mastitis rate that could not be ruled out in this
case.” The court noted that there was evidence that Roskop
Dairy was not following proper hygiene procedures to prevent
the spread of mastitis. Indeed, the court noted, the somatic
cell counts indicated a mastitis problem before the Dematron
was installed.
   The court further noted that Midwest’s expert, Patrick
Gorden, testified that there was no scientific basis to con-
clude that the detacher system caused mastitis or decreased
milk production. Rather, Gorden testified that the mastitis was
preexisting and likely exacerbated by hot weather and Roskop
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Dairy’s failure to implement a milk quality program and to
properly maintain the milking system. Gorden’s affidavit is
not in the record and apparently was not entered into evidence
at the summary judgment hearing.
   Finally, the court noted that Hunt opined that Roskop Dairy’s
failure to properly maintain the vents caused the mastitis. The
court noted that Roskop had failed to present any expert to
contradict Hunt’s expert opinion.
   The court reasoned that the fact the detacher units came
off under vacuum did not in itself demonstrate a product
defect. Although parameter settings were changed throughout
the installation process, there was no evidence that any settings
were incorrect or defective. While, under Genetti v. Caterpillar,
Inc.,2 proof that a warranted product is defective may be
circumstantial and inferred from the evidence, the court con-
cluded that Genetti was inapplicable. There were various pos-
sible causes of the increase in the somatic cell count or for the
units detaching under vacuum, which were beyond the normal
experience and understanding of the jury.
   The court concluded that expert testimony was required for
a jury to determine which component parts or settings of the
milking system caused it to come off under vacuum. Expert
testimony was also required for the jury to determine which,
among a number of possible causes of the spike in mastitis
in the herd, was more probable. Roskop Dairy had no such
expert testimony.
                     Prejudgment Interest
   The court subsequently granted summary judgment in favor
of Midwest on its counterclaim for the remaining principal
due of $78,026.56 plus prejudgment interest. Because the con-
tract did not provide for interest, the court applied Neb. Rev.
Stat. § 45-104 (Reissue 2010):
         Unless otherwise agreed, interest shall be allowed
      at the rate of twelve percent per annum on money due

 2	
      Genetti v. Caterpillar, Inc., 261 Neb. 98, 621 N.W.2d 529 (2001).
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     on any instrument in writing, or on settlement of the
     account from the day the balance shall be agreed upon,
     on money received to the use of another and retained
     without the owner’s consent, express or implied, from
     the receipt thereof, and on money loaned or due and
     withheld by unreasonable delay of payment. Unless oth-
     erwise agreed or provided by law, each charge with
     respect to unsettled accounts between parties shall bear
     interest from the date of billing unless paid within thirty
     days from the date of billing.
   The court observed that Midwest sent a payment request to
Roskop Dairy which bore a date of October 14, 2008, but there
was no evidence of when it was actually sent. Therefore, the
court utilized the date of November 1, because Roskop Dairy
admitted that the outstanding principal was owed to Midwest
as of November 1. The court utilized the rate of 8 percent per
annum rather than the statutory 12 percent, because 8 percent
was what Midwest had requested. The court did not expressly
discuss whether there had been a “reasonable controversy”
over the amount due to Midwest.3
                 ASSIGNMENTS OF ERROR
   Roskop Dairy asserts that the district court erred by (1)
excluding the testimony of Wailes, (2) denying Roskop Dairy’s
motion to compel, (3) granting the defendants’ motions for
summary judgment, and (4) awarding prejudgment interest
to Midwest.
                  STANDARD OF REVIEW
  [1,2] We review de novo whether the trial court applied the
correct legal standards for admitting an expert’s testimony.4
We review for abuse of discretion how the trial court applied

 3	
      See, e.g., Wilson Concrete Co. v. A. S. Battiato Constr. Co., 196 Neb. 185,
      188, 241 N.W.2d 819, 821 (1976).
 4	
      King v. Burlington Northern Santa Fe Ry. Co., 277 Neb. 203, 762 N.W.2d
      24 (2009).
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the appropriate standards in deciding whether to admit or
exclude an expert’s testimony.5
   [3] In reviewing a summary judgment, an appellate court
views the evidence in the light most favorable to the party
against whom the judgment was granted and gives that
party the benefit of all reasonable inferences deducible from
the evidence.6
   [4] Generally, the control of discovery is a matter for
judicial discretion, and decisions regarding discovery will be
upheld on appeal in the absence of an abuse of discretion.7
   [5] Prejudgment interest may be awarded only as provided
in Neb. Rev. Stat. § 45-103.02 (Reissue 2010), and whether
prejudgment interest should be awarded is reviewed de novo
on appeal.8
                          ANALYSIS
         Exclusion of Wailes’ Testimony and Whether
              There Was M aterial Issue of Fact
   [6,7] The central question in this case is whether we should
affirm the district court’s order of summary judgment for
the defendants. A motion for summary judgment shall be
granted where there is no genuine issue as to any material
fact and the moving party is entitled to judgment as a mat-
ter of law.9 Failure of proof concerning an essential element
of the nonmoving party’s case necessarily renders all other
facts immaterial.10

 5	
      Id.
 6	
      Rent-A-Roofer v. Farm Bureau Prop. & Cas. Ins. Co., 291 Neb. 786, 869
      N.W.2d 99 (2015).
 7	
      Farmington Woods Homeowners Assn. v. Wolf, 284 Neb. 280, 817 N.W.2d
      758 (2012).
 8	
      Countryside Co-op v. Harry A. Koch Co., 280 Neb. 795, 790 N.W.2d 873
      (2010).
 9	
      See Rent-A-Roofer v. Farm Bureau Prop. & Cas. Ins. Co., supra note 6.
10	
      See Celotex Corp. v. Catrett, 477 U.S. 317, 106 S. Ct. 2548, 91 L. Ed. 2d
      265 (1986).
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   [8-10] A party moving for summary judgment makes a
prima facie case for summary judgment by producing enough
evidence to demonstrate that the movant is entitled to judg-
ment if the evidence were uncontroverted at trial.11 Once the
moving party makes a prima facie case, the burden shifts to
the party opposing the motion to produce admissible contra-
dictory evidence showing the existence of a material issue of
fact that prevents judgment as a matter of law.12 Conclusions
based on guess, speculation, conjecture, or a choice of pos-
sibilities do not create material issues of fact for the purposes
of summary judgment13; the evidence must be sufficient to
support an inference in the nonmovant’s favor without the fact
finder engaging in guesswork.14
   The defendants made a prima facie case for summary
judgment through expert testimony that poor maintenance of
the vents in the claws was the proximate cause of the units
detaching under vacuum and, thus, of any mastitis resulting
therefrom. Without endorsing the sufficiency of the evidence
on any other aspect of Roskop Dairy’s case, we focus our
analysis on this element of mechanical causation. Doing so,
we conclude that Roskop Dairy failed to produce admissible
contradictory evidence creating a material issue of fact to rebut
the defend­ants’ prima facie case.
   Wailes neither purported to opine on the mechanical cause
of the units detaching under vacuum, nor was he qualified
to do so. And Roskop Dairy did not present other sufficient
circumstantial evidence that could lead a reasonable person to
accept its theory that the Dematron was the proximate cause

11	
      Chicago Lumber Co. of Omaha v. Selvera, 282 Neb. 12, 809 N.W.2d 469
      (2011).
12	
      See, Borrenpohl v. DaBeers Properties, 276 Neb. 426, 755 N.W.2d 39
      (2008); New Tek Mfg. v. Beehner, 270 Neb. 264, 702 N.W.2d 336 (2005).
13	
      Marksmeier v. McGregor Corp., 272 Neb. 401, 722 N.W.2d 65 (2006);
      Richards v. Meeske, 268 Neb. 901, 689 N.W.2d 337 (2004).
14	
      C.E. v. Prairie Fields Family Medicine, 287 Neb. 667, 844 N.W.2d 56
      (2014).
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of the purported injury. As will be explained in more detail
below, we agree with the district court that Roskop Dairy’s
reliance on the malfunction theory is misplaced, because it
is limited to proving a specific defect through circumstantial
evidence and because Roskop Dairy failed to present evidence
that could establish the elements of the malfunction theory.
Any other circumstantial evidence that Roskop Dairy relies on
to rebut the defendants’ prima facie case for summary judg-
ment amounts to speculative reasoning based on observations
of a temporal correlation.
   [11] All implied warranty theories of recovery and strict
liability claims for manufacturing defect, design defect, or fail-
ure to warn seek to recover for a “defect.”15 Express warranty
claims are not merged with implied warranty claims or strict
liability claims due to the “‘dickered’” aspects of the indi-
vidual bargain,16 but express warranty claims, like implied war-
ranty theories and strict liability claims, require a showing that
the goods were defective.17 While a “defect” traditionally falls
under the category of either a design, manufacturing, or warn-
ing defect, “defective” installation is also cognizable under the
Uniform Commercial Code’s breach of warranty theories when
the installation is incident to the sale; in other words, when the
purchase is for a system that is dependent upon proper instal-
lation.18 And the user of a product may also assert a cause of
action for negligent installation concurrently with actions under
express and implied warranty theories.19
   [12-14] Whether a plaintiff is proceeding under negligence,
defect theories, or breach of express warranty, proximate cause

15	
      See Freeman v. Hoffman-La Roche, Inc., 260 Neb. 552, 618 N.W.2d 827
      (2000).
16	
      Id. at 574, 618 N.W.2d at 844.
17	
      Genetti v. Caterpillar, Inc., supra note 2.
18	
      See, Mennonite Deaconess Home & Hosp. v. Gates Eng’g Co., 219 Neb.
      303, 363 N.W.2d 155 (1985); 3 American Law of Products Liability 3d
      § 37:12 (2015).
19	
      3 American Law of Products Liability 3d, supra note 18.
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is a necessary element of the plaintiff’s case.20 Proximate cause
is the cause that in a natural and continuous sequence unbro-
ken by an efficient intervening cause, produces the injury,
and without which the injury would not have occurred.21 To
establish proximate cause, the plaintiff must meet three basic
requirements: (1) Without the negligent action, the injury
would not have occurred, commonly known as the “but for”
rule or “cause in fact”; (2) the injury was a natural and prob-
able result of the negligence; and (3) there was no efficient
intervening cause.22
   [15] In this case, proving the elements of defect/negligence
and proximate cause involves the mechanical functioning of
a dairy farm milking system and its various component parts.
Such technical matters are outside the scope of ordinary expe-
rience. Findings of fact as to technical matters beyond the
scope of ordinary experience are usually not warranted in the
absence of expert testimony supporting such findings.23
   Hunt testified that the clogged and upside-down vents
reported by Nissen and Farrier were the cause of the milking
units detaching under vacuum. Roskop presented no reliable
expert opinion to the contrary. Roskop admitted that he was
not an expert on milking machines. Wailes likewise stated

20	
      See, Powell v. Harsco Corp., 209 Ga. App. 348, 433 S.E.2d 608 (1993); 1
      American Law of Products Liability 3d § 4:1 (2007).
21	
      See, Stahlecker v. Ford Motor Co., 266 Neb. 601, 667 N.W.2d 244 (2003);
      Pendleton Woolen Mills v. Vending Associates, Inc., 195 Neb. 46, 237
      N.W.2d 99 (1975).
22	
      See, Hughes v. School Dist. of Aurora, 290 Neb. 47, 858 N.W.2d 590
      (2015); Belgum v. Mitsuo Kawamoto & Assoc., 236 Neb. 127, 459 N.W.2d
      226 (1990); Daniels v. Andersen, 195 Neb. 95, 237 N.W.2d 397 (1975).
23	
      See, McVaney v. Baird, Holm, McEachen, 237 Neb. 451, 466 N.W.2d 499
      (1991); Overland Constructors v. Millard School Dist., 220 Neb. 220, 369
      N.W.2d 69 (1985). See, also, Green v. Box Butte General Hosp., 284 Neb.
      243, 818 N.W.2d 589 (2012); State v. Aguilar, 268 Neb. 411, 683 N.W.2d
      349 (2004); Eiting v. Godding, 191 Neb. 88, 214 N.W.2d 241 (1974);
      Clark v. Village of Hemingford, 147 Neb. 1044, 26 N.W.2d 15 (1947).
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clearly that he was not an expert in the design, installation,
diagnosis, settings, or repair of milking machine equipment.
Wailes stated that he did not know what, if anything, was
wrong with the Dematron and had no opinion about the param-
eter settings.
   Roskop points out that Wailes confirmed that “a properly
operating detacher system” does not “come off under pressure
as described by . . . Roskop.” This statement, in combination
with Roskop’s testimony, may support the occurrence of some
kind of malfunction of the milking system. But this was not
an opinion as to whether the Dematron was the cause of that
malfunction. To the contrary, Wailes acknowledged that there
were many possible mechanical causes of the units coming off
under vacuum, which have nothing to do with the Dematron.
Wailes agreed that it would not be “scientific reasoning” to
conclude that the Dematron was responsible for the claws’
detaching under vacuum.
   Even if Wailes had been qualified to opine on which com-
ponent part of the milking system caused the units to detach
under vacuum, and had actually attempted to do so, such opin-
ion would be unreliable under Schafersman v. Agland Coop.24
The expert must have “good grounds” for his or her belief “in
every step of the analysis.”25 The term “good grounds” means
an inference or assertion derived by scientific method and sup-
ported by appropriate validation.26
   [16] Wailes testified, “[M]y analysis is that there had to be
some event to trigger somatic cell counts to take that much
of a spike” and “[m]y main concern at the time was the tim-
ing of the events, and the timing of the events match up to
the installation.” It is well settled that a causation opinion
based solely on a temporal relationship is not derived from the

24	
      Schafersman v. Agland Coop, supra note 1.
25	
      King v. Burlington Northern Santa Fe Ry. Co., supra note 4, 277 Neb. at
      227, 762 N.W.2d at 43.
26	
      Id.
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scientific method and is therefore unreliable.27 Such an opinion
is also unreliable because it is not based upon sufficient facts
or data.28
   An expert can challenge hypotheses formulated through the
observation of association29 or utilize a challenge/­dechallenge/
rechallenge methodology, or the expert can systematically
eliminate other reasonably probable causes in conjunction with
observation of temporal correlation.30 But the reliability of
such methodologies to support a causation opinion is directly
related to the degree of scientific rigor.31 Wailes’ assertion
that “when you try to eliminate events that could occur dur-
ing that period of time, the one that you can’t eliminate is the
installation of new equipment that was not working properly
at the time,” and his further assertions that the feed had not
changed, that Roskop had a good reputation, and that Roskop
had unspecified protocols in place, demonstrate little scientific
rigor. Furthermore, this testimony concerns, at most, alternate
etiologies of mastitis and not the alternate mechanical causes
of the malfunction. Thus, to the extent that Roskop makes an
argument that the court should have admitted Wailes’ testimony
for purposes of mechanical causation, we find that the district
court did not err.
   Roskop alternatively argues that expert testimony is not
required to create a material issue of fact rebutting the

27	
      See, Porter v. Whitehall Laboratories, Inc., 9 F.3d 607 (7th Cir. 1993);
      Derzavis v. Bepko, 766 A.2d 514 (D.C. 2000); Terry v. Bd. of Mental
      Retardation, 165 Ohio App. 3d 638, 847 N.E.2d 1246 (2006), reversed in
      part on other grounds sub nom. Terry v. Caputo, 15 Ohio St. 3d 351, 875
      N.E.2d 72 (2007). See, also, e.g., Schafersman v. Agland Coop, supra note
      1; Carlson v. Okerstrom, 267 Neb. 397, 675 N.W.2d 89 (2004).
28	
      King v. Burlington Northern Santa Fe Ry. Co., supra note 4.
29	
      See id.
30	
      See Heller v. Shaw Industries, Inc., 167 F.3d 146 (3d Cir. 1999). See, also,
      Carlson v. Okerstrom, supra note 27.
31	
      See McClain v. Metabolife Intern., Inc., 401 F.3d 1233 (11th Cir. 2005).
      See, also, Glastetter v. Novartis Pharmaceuticals Corp., 252 F.3d 986 (8th
      Cir. 2001).
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defendants’ prima facie case for summary judgment. In making
this argument, Roskop apparently relies on the “malfunction
theory.” The malfunction theory is based on the same principle
underlying res ipsa loquitur, which permits a fact finder to
infer negligence from the circumstances of the incident, with-
out resort to direct evidence of the wrongful act.32
   [17] Under the malfunction theory, also sometimes called
the indeterminate defect theory or general defect theory,33 a
plaintiff may prove a product defect circumstantially, without
proof of a specific defect, when (1) the incident causing the
harm was of a kind that would ordinarily occur only as a result
of a product defect and (2) the incident was not, in the particu-
lar case, solely the result of causes other than a product defect
existing at the time of sale or distribution.34
   The malfunction theory should be utilized with the utmost
of caution. Although some circumstances may justify the use
of the malfunction theory to bridge the gap caused by miss-
ing evidence, the absence of evidence does not make a fact
more probable but merely lightens the plaintiff’s evidentiary
burden despite the fact that the missing evidence might well
have gone either way, and this rationale is too often subject
to misapplication by courts in situations in which evidence is
actually available.35

32	
      Restatement (Third) of Torts: Products Liability § 3, comment a. (1998).
33	
      See, id., § 3; David G. Owen, Manufacturing Defects, 53 S.C. L. Rev. 851
      (2002). See, also, e.g., Sochanski v. Sears, Roebuck and Co., 621 F.2d 67
      (3d Cir. 1980); Stewart v. Ford Motor Co., 553 F.2d 130 (D.C. Cir. 1977);
      Higgins v. General Motors Corp., 287 Ark. 390, 699 S.W.2d 741 (1985);
      Wakabayashi v. Hertz, 66 Haw. 265, 660 P.2d 1309 (1983); Gillespie v. R.
      D. Werner Co., 71 Ill. 2d 318, 375 N.E.2d 1294, 17 Ill Dec. 10 (1978);
      Stackiewicz v. Nissan Motor Corp., 100 Nev. 443, 686 P.2d 925 (1984);
      Moraca v. Ford Motor Co., 66 N.J. 454, 332 A.2d 599 (1975); Brownell v.
      White Motor Corp., 260 Or. 251, 490 P.2d 184 (1971).
34	
      Genetti v. Caterpillar, Inc., supra note 2; Restatement, supra note 32, § 3.
35	
      See Metro. Property & Cas. Ins. Co. v. Deere & Co., 302 Conn. 123, 25
      A.3d 571 (2011).
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   We have explained that as a matter of policy we allow
circumstantial proof of a product defect without evidence of
the specific defect because in many instances the dealer or
manufacturer has either purposefully or inadvertently tam-
pered with the evidence. Further, in light of the technological
complexity in proving a specific defect, “forcing consumers to
identify the cause, rather than the effect, of a defect would be
unrealistically burdensome.”36
   The malfunction theory is narrow in scope. The malfunction
theory simply provides that it is not necessary for the plaintiff
to establish a specific defect so long as there is evidence of
some unspecified dangerous condition or malfunction from
which a defect can be inferred37—the malfunction itself is cir-
cumstantial evidence of a defective condition.38 The malfunc-
tion theory does not alter the basic elements of the plaintiff’s
burden of proof and is not a means to prove proximate cause
or damages.39
   Other courts have set forth a nonexhaustive list of the kind
of circumstantial evidence that may be used to support a rea-
sonable inference of a specific defect. In DeWitt v. Eveready
Battery Co., Inc.,40 for example, the court illustrated six evi-
dentiary factors that a plaintiff may present to create a genuine
issue of fact on the element of defect through circumstantial
evidence: (1) the malfunction of the product; (2) expert tes-
timony as to a possible cause or causes; (3) the timeframe of
the malfunction’s occurrence after the plaintiff first obtained
the product and other relevant history of the product, such
as its age and prior usage by the plaintiff and others, includ-
ing evidence of misuse, abuse, or similar relevant treatment

36	
      Genetti v. Caterpillar, Inc., supra note 2, 261 Neb. at 114, 621 N.W.2d. at
      542.
37	
      1 American Law of Products Liability 3d, supra note 20, § 1:15 (2013).
38	
      Ducko v. Chrysler Motors Corp., 433 Pa. Super. 47, 639 A.2d 1204 (1994).
39	
      See Sochanski v. Sears, Roebuck and Co., supra note 33.
40	
      DeWitt v. Eveready Battery Co., Inc., 355 N.C. 672, 565 S.E.2d 140
      (2002).
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before it reached the defendant; (4) similar incidents, when
accompanied by proof of substantially similar circumstances
and reasonable proximity in time; (5) elimination of other pos-
sible causes of the accident; and (6) proof tending to establish
that such an accident would not occur absent a manufactur-
ing defect.
   Roskop relies on Genetti v. Caterpillar, Inc., in which we
applied the principles of the malfunction theory and some of
these factors to conclude that the circumstantial evidence of
a defect was sufficient to support a verdict in the plaintiffs’
favor.41 The plaintiffs in Genetti sought recovery for the total
failure of their truck’s engine. Subsequent to purchasing the
truck new, multiple engine failures had occurred. The defend­
ant had first repaired the engine and, upon subsequent failures,
replaced it. In replacing the engine, the defendant utilized some
components from the old engine. The defendant did not keep
records of which components of the engine were replaced and
which were reused. Eventually, the truck was sold, and the
defendant replaced the engine again after another engine fail-
ure subsequent to the purchase.
   The plaintiffs’ expert witness, a mechanic, admitted he was
not an expert in engine design, but illustrated his expertise in
repairing, rebuilding, and overhauling the kind of engine at
issue. The mechanic reviewed documentation of the repairs,
photographs, and interviews, and concluded that a coolant
leak caused the engine failures. The mechanic negated alter-
nate, reasonably possible causes of the engine failures. The
mechanic was unsure whether the coolant leak was specifi-
cally due to a cracked head, cracked head gasket, or some
other failure allowing the intrusion of coolant. He testified,
however, that the uncontroverted testimony concerning the
use of the truck was not a misuse that should have resulted in
engine failure.
   We held that because the plaintiffs presented evidence elim-
inating abuse or misuse as the alternate cause of the engine

41	
      Genetti v. Caterpillar, Inc., supra note 2.
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failure, it was reasonable for a jury to conclude that if the fail-
ure was not due to improper use of the truck, then it was due
to a defect, such as one of those suggested by the mechanic.42
We held that the plaintiffs were not required to prove the spe-
cific defect that caused the failures in order to prove that the
engine was defective.43
   But more apposite to the facts of this case is Wilgro, Inc.
v. Vowers & Burback.44 In Wilgro, Inc., although (unlike here)
there was direct evidence of a specific defect, we held that the
circumstantial evidence was insufficient to support a finding of
proximate cause. The defendant in Wilgro, Inc. had provided
the plaintiff with feed supplements for the plaintiff’s cattle that
contained slightly higher levels of nonprotein nitrogen, urea,
than warrantied. Shortly after obtaining the feed, the cattle
became sick. Some eventually died. Autopsies on some of the
cattle were performed, and they were found to have died of
urea poisoning.
   Other causation theories unrelated to the defect and sup-
ported by the record could account for the poisoning. For
instance, given the method of merely spreading the supplement
on the bottom of a truck and pouring silage on top where the
cattle “free fed,” the feed could have been improperly mixed
with the supplement. Or, some cows could have eaten more
feed than they were allotted. Furthermore, the plaintiff’s own
immature silage could account for the symptoms observed
in the majority of the animals that the plaintiff claimed had
been injured.
   [18,19] We explained that circumstantial evidence is not
sufficient to sustain a verdict that depends solely thereon
unless the circumstances proved by the evidence are of such a
nature and so related to each other that the conclusion reached
by the jury is the only one that can fairly and reasonably be

42	
      See id.
43	
      Id.
44	
      Wilgro, Inc. v. Vowers & Burback, 190 Neb. 369, 208 N.W.2d 698 (1973).
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drawn therefrom.45 Where, instead, under the facts viewed in a
light most favorable to the nonmoving party, the nonexistence
of the fact to be inferred is just as probable as its existence, the
conclusion that it exists is a matter of speculation, surmise, and
conjecture, and a jury will not be permitted to draw it.46 We
concluded in Wilgro, Inc. that the plaintiff had failed to adduce
evidence that would lead the reasonable person to accept the
plaintiff’s theory of causation over those theories presented by
the defendant.
   In Pendleton Woolen Mills v. Vending Associates, Inc.,47 a
negligence case, we similarly found the circumstantial evi-
dence to be insufficient for any determination of proximate
cause in the plaintiff’s favor to rise above speculation. The
plaintiff’s building had been damaged by the flooding of a
sticky substance. A large amount of water and syrup was found
on the floor in the vicinity of a soft drink machine, which was
the apparent source of the flooding. The machine obtained its
water supply from a water pipe in the building, to which it
was connected by copper tubing. The defendant was allegedly
responsible for the maintenance of the machine.
   We found “a total lack of evidence establishing that any
negligence . . . was the ‘proximate cause’ of either the leak
or the damages; or to state it more accurately, that there was
any ‘causation in fact’ between the alleged negligence, and
the occurrence and the water damage.”48 Only one nonexpert
witness reported a hearsay statement loosely attributing the
leak to a malfunctioning shutoff valve. And there was no
proof that the absence of regular inspection was a substan-
tial factor in causing the valve to malfunction, if it indeed
did. Nor was there evidence that but for the absence of such
inspection, the leak would not have occurred. In particular,

45	
      Id.
46	
      See Ehler et ux v. Portland Gas & Coke Co., 223 Or. 28, 352 P.2d 1102
      (1960).
47	
      Pendleton Woolen Mills v. Vending Associates, Inc., supra note 21.
48	
      Id. at 50, 237 N.W.2d at 102.
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there was no evidence indicating the location of the shutoff
valve in the machine and whether a leak could be detected.
Again, we said that speculation and conjecture are not suf-
ficient to establish causation; there must be something more
that will lead a reasonable mind to one conclusion rather
than another.49
   In considering Roskop Dairy’s argument that the malfunc-
tion theory applies, we first note that there is no apparent loss
of the evidence of a specific defect, because there is a record
of the parameter settings. Indeed, from these records, Roskop
has suggested a very specific theory that the detach delay
setting of 3 seconds was defective and negligent and that it
should have been 10 seconds, the setting it was changed to in
late July 2008. While we have found little case law specifi-
cally addressing whether the malfunction theory applies when
there is no loss of evidence or when there is an allegation of
a specific defect, we find no cases that have done so. And we
observe that the related doctrine of res ipsa loquitur does not
apply when specific acts of negligence are alleged or there is
evidence of the precise cause of the accident.50
   Assuming that the malfunction theory can be utilized when
there has been no loss of evidence relating to the alleged spe-
cific defect, Roskop presented insufficient evidence to estab-
lish a material issue of fact supporting the malfunction theory.
Roskop presented no reliable evidence that the incident causing
the harm was of a kind that would ordinarily occur only as a
result of a product defect, as he had no expert on milking sys-
tems. And he presented no reliable evidence negating causes
other than the alleged product defect—despite undisputed evi-
dence that detachment under vacuum could have multiple pos-
sible mechanical sources.51 Roskop did not even present evi-
dence negating Nissen’s and Farrier’s testimony that the vents

49	
      Pendleton Woolen Mills v. Vending Associates, Inc., supra note 21.
50	
      See Maly v. Arbor Manor, Inc., 225 Neb. 276, 404 N.W.2d 419 (1987).
51	
      See, Genetti v. Caterpillar, Inc., supra note 2; Restatement, supra note 32,
      § 3.
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of the lenses had been placed upside down and that nonvented
lenses had been placed in the claws.
   [20,21] In any event, the malfunction theory would not
serve to create a material issue on the element of proxi-
mate cause, because it is a theory only utilized to prove the
element of defect.52 Roskop Dairy seeks more than just a
bridge over the gap of difficult-to-obtain and highly techni-
cal evidence of a specific defect. Roskop attempts to create
a material issue of fact on little more than his observation of
a temporal correlation. But the line between impermissible
speculation and reasonable inferences is drawn by the laws
of logic.53 And reasoning causation from temporal correlation
represents a logical fallacy. A conclusion based upon such
reasoning is not a reasonable inference but is mere specula-
tion and conjecture.54
   We find no merit to Roskop’s argument that Hunt’s testi-
mony confirming that the settings for the detach delay were
changed from 3 seconds to 10 seconds rebuts the defendants’
prima facie case. It would be speculative to derive any conclu-
sion as to either negligence/defect or proximate cause based on
the record of the parameter settings without an expert opinion
interpreting those settings in the larger context of the milking
system. Roskop Dairy’s conclusion based on the correlation of
the 3-second setting to detachment under vacuum and of the
10-second setting to no detachment under vacuum remains at
its core an application of the logical fallacy that correlation
equals causation.

52	
      See, White v. Mazda Motor of America, Inc., 313 Conn. 610, 99 A.3d 1079
      (2014); Barnish v. KWI Bldg. Co., 916 A.2d 642 (Pa. 2007).
53	
      Tose v. First Pennsylvania Bank, N.A., 648 F.2d 879 (3d Cir. 1981),
      abrogated on other grounds, Griggs v. Provident Consumer Discount Co.,
      459 U.S. 56, 103 S. Ct. 400, 74 L. Ed. 2d 225 (1982).
54	
      See, Sunward Corp. v. Dun & Bradstreet, Inc., 811 F.2d 511 (10th Cir.
      1987); Loesch v. United States, 645 F.2d 905 (Ct. Cl. 1981); Dodge Motor
      Trucks, Inc. v. First Nat. Bank of Omaha, 519 F.2d 578 (8th Cir. 1975);
      Genesee M. B. & T. Co. v. Payne, 6 Mich. App. 204, 148 N.W.2d 503
      (1967).
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   At oral arguments, Roskop Dairy also suggested that sum-
mary judgment was improper because cross-examination of
Hunt at trial might lead to a more favorable and direct admis-
sion regarding the Dematron settings and their connection to
the detachment under vacuum. In two depositions, Roskop
Dairy has failed to obtain an opinion from Hunt that the
Dematron settings during the relevant time period were in any
way improper or a substantial factor in causing the units to
detach under vacuum. Roskop’s hope that this testimony might
change at trial is insufficient to rebut the defendants’ prima
facie case for summary judgment.
   Under the malfunction theory or otherwise, Roskop Dairy
failed to present evidence from which a jury could deter-
mine, without resorting to speculation, that the Dematron was
the proximate cause of the alleged injury to Roskop Dairy’s
cows. The district court accordingly did not err in granting the
defendants summary judgment. Although we share the district
court’s concerns over the lack of evidence that the Dematron
was defectively or negligently installed and the lack of reli-
able evidence causally linking the detachment under vacuum
to the medical condition of mastitis, we need not examine
those aspects of the district court’s ruling in order to affirm
its decision.
                    Considering Testimony
                       Not in Evidence
   We find no merit to Roskop Dairy’s assertion that we
should reverse the district court’s order because it errone-
ously relied on facts not in evidence when it granted sum-
mary judgment. Roskop argues that in reasoning that there are
several causes of mastitis, the district court erroneously relied
on Gorden’s affidavit, which was not entered into evidence.
Roskop argues that, even “more egregiously,” the district court
relied on Wailes’ excluded testimony and upon the deposition
of Slattery, which was admitted for limited purposes only.55

55	
      Brief for appellant at 28.
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Roskop argues that the district court could not rely on any
aspect of Wailes’ testimony, because neither party reoffered
it for summary judgment. Finally, Roskop characterizes the
district court’s order as expressing an improper factual finding
that other factors could have contributed to or caused mastitis
in the herd.
   It is unclear how Roskop believes it helpful to argue that
Wailes’ deposition was not in evidence for purposes of sum-
mary judgment. The absence of Wailes’ testimony in its entirety
provides only less evidence from which we could conclude
there was a material issue of fact. And such argument ren-
ders fruitless Roskop Dairy’s argument that Wailes’ testimony
should not have been excluded.
   Furthermore, the alternate causes of mastitis that Roskop
believes the court erred in considering were generally listed
in other admitted testimony, such as Roskop’s deposition
and the limited receipt of Slattery’s deposition. A summary
judgment hearing is similar to a bench trial of an action at
law; thus, ordinarily, the erroneous admission of evidence in
a summary judgment hearing is not reversible error if other
relevant evidence, admitted without objection or properly
admitted over objection, sustains the trial court’s necessary
factual findings.56
   Regardless, none of Roskop Dairy’s arguments on this
assignment of error concern the absence of reliable evidence
rebutting the defendants’ prima facie case that improper main-
tenance by Roskop Dairy employees of the physical compo-
nents of the milking system was the proximate cause of the
malfunction. Therefore, these arguments are not grounds for
reversal under our reasoning set forth above.
                    Denying Discovery
  Roskop Dairy also argues that the district court erred in
denying its motion to compel. Roskop Dairy argues vaguely

56	
      John Markel Ford v. Auto-Owners Ins. Co., 249 Neb. 286, 543 N.W.2d
      173 (1996).
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that there is a series of correspondence listed on the privilege
log between an employee of Midwest and its designated expert
witness. Roskop Dairy further argues generally that it was
entitled to discover underlying facts contained in privileged
documents, such as parameter settings and changes, facts
regarding the operation and maintenance of the system, and
facts relating to the investigations of the malfunction of the
system. Lastly, Roskop Dairy asserts broadly that information
and parameter settings gathered by Hunt in the ordinary course
of business were not privileged.
   [22] The party asserting error in a discovery ruling bears
the burden of showing that the ruling was an abuse of dis-
cretion.57 For our review, Roskop Dairy requested only that
sealed exhibit 9 be included in the bill of exceptions. It
is incumbent upon the party appealing to present a record
which supports the errors assigned. Neb. Rev. Stat. § 25-1140
(Reissue 2008) and Neb. Ct. R. App. P. § 2-105(B)(1)(b) (rev.
2010) place the burden on the appellant to file a praecipe
identifying the matter to be contained in the bill of excep-
tions. Thus, we consider Roskop’s assignment of error only
as pertains to exhibit 9.
   After an in camera review, the district court found that the
documents contained in exhibit 9 were protected by attorney-
client privilege and work-product privilege. The court also
noted that GEA had produced for Roskop Dairy its most
knowledgeable witness, Hunt, to be deposed on the topics
contained in the deposition notice duces tecum attached to
Roskop Dairy’s motion to compel discovery. Further, the
court found that GEA had produced the records required by
Roskop Dairy’s discovery request, except for those protected
by privilege, but that Roskop Dairy had difficulty opening
certain computer records and that Hunt did not have them
all with him during his deposition. Because of this, the
court allowed Roskop Dairy great “latitude in discovery”
and ordered that Roskop Dairy be able to reconvene the

57	
      U.S. Bank Nat. Assn. v. Peterson, 284 Neb. 820, 823 N.W.2d 460 (2012).
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deposition of Hunt and that Hunt should have with him cop-
ies of any records he relied on for his testimony. That second
deposition occurred, and Hunt brought with him records of
the Dematron parameter settings.
   We find no abuse of discretion in the district court’s order
partially denying Roskop Dairy’s motion to compel. There is
no evidence that Roskop Dairy was denied discovery of rel-
evant underlying facts or business records pertaining to param-
eter settings or to any changes or facts regarding the operation
and maintenance of the system. Furthermore, the court did
not abuse its discretion in finding the documents contained in
sealed exhibit 9 to be protected by the attorney-client privilege
and the work-product privilege.
   We have recognized that it is difficult to show that a party
has been prejudiced by a discovery order, or that the question
is not moot; and the harmless error doctrine, together with
the broad discretion the discovery rules vest in the trial court,
will bar reversal save under very unusual circum­      stances.58
This case is no exception. We find no merit to Roskop
Dairy’s assignment of error concerning the motion to com-
pel discovery.
                     Prejudgment Interest
   Finally, we turn to Roskop Dairy’s argument that the district
court erred in granting Midwest prejudgment interest on its
counterclaim for the unpaid amount of the purchase agree-
ment. Prejudgment interest may be awarded only as provided
in § 45-103.02, and whether prejudgment interest should be
awarded is reviewed de novo on appeal.59
   [23] A claim is liquidated for purposes of prejudgment
interest when there is no reasonable controversy as to both the
amount due and the plaintiff’s right to recover.60 The amount

58	
      Brozovky v. Norquest, 231 Neb. 731, 437 N.W.2d 798 (1989).
59	
      Countryside Co-op v. Harry A. Koch Co., supra note 8.
60	
      Brook Valley Ltd. Part. v. Mutual of Omaha Bank, 285 Neb. 157, 825
      N.W.2d 779 (2013). See, also, § 45-103.02(2).
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due was uncontroverted. But we conclude that, given the tech-
nical complexity of the matters at issue, until discovery was
completed, there was a reasonable controversy over Roskop
Dairy’s right to recover. The fact that summary judgment was
properly granted is not decisive of whether there was until
that point a reasonable controversy over a plaintiff’s right to
recover.61 We therefore reverse the district court’s order grant-
ing prejudgment interest on Midwest’s counterclaim.
                         CONCLUSION
   The opponent of a motion for summary judgment must be
given the benefit of every reasonable inference from the evi-
dence, but not inferences based on guess or speculation.62 The
defendants made a prima facie case that there was no issue of
fact that components other than the Dematron were the proxi-
mate cause of the detachment under vacuum. Roskop’s eyewit-
ness observation of a temporal correlation between installation
of the Dematron and the units detaching under vacuum calls
for speculation and is insufficient to create an issue of fact on
the essential element of proximate cause. We therefore affirm
the order of the district court granting summary judgment for
the defendants in Roskop Dairy’s action against them. But we
reverse the district court’s order granting prejudgment interest
on Midwest’s counterclaim.
                       A ffirmed in part, and in part reversed.
   Heavican, C.J., participating on briefs.
   Stephan, J., not participating in the decision.
   Wright, J., not participating.

61	
      See, Countryside Co-op v. Harry A. Koch Co., supra note 8; Dutton-
      Lainson Co. v. Continental Ins. Co., 279 Neb. 365, 778 N.W.2d 433
      (2010).
62	
      See Giordano v. Sherwood, 968 A.2d 494 (D.C. 2009).
