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Voluntary heat stress abatement system for dairy cows: Does it mitigate the effects of heat stress on physiology and behavior?

Open AccessPublished:November 21, 2022DOI:https://doi.org/10.3168/jds.2022-21802

      ABSTRACT

      Many cooling strategies are used to keep cows in thermal homeostasis; however, most of them are applied to the group level, commonly at the feed bunk or milking parlor. The variance of heat stress effects on animals are well known, but with more individualized management in dairy farms, group cooling opportunities are becoming restricted. It is known that dairy cattle are variable in their responses to an increase in heat load. Thus, the first objective of this study was to investigate the effect of 2 mandatory soakings at the exit of the milking parlor and free access to a voluntary soaking system compared with cows with access to a voluntary soaking system only, with no mandatory soakings. The second objective of this study was to assess the heat abatement capability of voluntary soaking of cows by assessing cow physiology, behavior, and milk production. Last, this study aimed to determine the individual use of the voluntary heat abatement system and its relationship with temperature-humidity index (THI). Fifteen mid-lactation Holstein cows were enrolled in this study and had free access to a motion-activated soaker (Cool Sense, Edstrom) located adjacent to the research pen for an 8-wk data collection period. Cows were paired according to parity, milk production, and body weight, and assigned a treatment with or without mandatory soakings twice per day. In the mandatory soaking treatment (MS), cows were soaked using a motion-activated soaker at the exit of the milking parlor and had free access to the voluntary soaker in the pen. Cows in the treatment without mandatory soakings (NMS) were not soaked at the exit of the milking parlor and had free access to the voluntary soaker in the pen. The effects of soaker treatment were analyzed using mixed linear models. The model included treatment, soaker uses per day, pair, mean daily THI, days in milk, daily milk yield, and interaction of treatment with mean daily THI. Study day was specified as a repeated measure, and cow as the subject, using an autoregressive structure. Also, we assessed the relationship of mean soaker use and THI against all variables. There was great individual variation in voluntary soaker use, ranging from 0 to 227 soakings/d (mean ± standard deviation, 13 ± 30 voluntary soakings/d). Treatment did not affect voluntary soaker use (MS, 12.4 ± 1.4 soakings/d; NMS, 14.8 ± 1.4 soakings/d), respiration rate (MS, 57.3 ± 0.4 breaths/min; NMS, 56.4 ± 0.4 breaths/min), or milk yield (MS, 36.5 ± 0.6 kg/d; NMS, 36.2 ± 0.6 kg/d). However, MS cows spent more time ruminating (MS, 558.6 ± 5.2 min/d; NMS, 543.4 ± 5.4 min/d). Temperature-humidity index had a positive relationship with voluntary soaker use and mean respiration rate. In conclusion, voluntary soaker use related positively to the THI, but no major productive, physiological, or behavioral differences were observed between soaking treatments. Furthermore, we found that voluntary soaker use is highly variable among cows and it was related positively to milk yield, where higher producing cows used the soaker more frequently.

      Key words

      INTRODUCTION

      Cows in environmental conditions that exceed their thermoneutral zone (5 to 25°C) (
      • McDowell R.E.
      Improvement of Livestock Production in Warm Climates.
      ) have increased metabolic requirements, increased respiration rate (RR), sweat, and pant to regulate body temperature (
      • Collier R.J.
      • Beede D.
      • Thatcher W.
      • Israel L.
      • Wilcox C.
      Influences of environment and its modification on dairy animal health and production.
      ). Temperature-humidity index (THI) is a common method of assessing heat stress affecting dairy cows, because it has been shown to be highly associated with production losses, health, and behavioral changes [see review by
      • Becker C.A.
      • Collier R.J.
      • Stone A.E.
      Invited review: Physiological and behavioral effects of heat stress in dairy cows.
      ]. Production losses have been found to occur at around THI ≥ 72 (
      • Armstrong D.V.
      Heat stress interaction with shade and cooling.
      ;
      • Ravagnolo O.
      • Misztal I.
      • Hoogenboom G.
      Genetic component of heat stress in dairy cattle, development of heat index function.
      ); however, behavioral and motivational changes were found to occur at lower THI, such as ≥68 (
      • De Rensis F.
      • Garcia-Ispierto I.
      • López-Gatius F.
      Seasonal heat stress: Clinical implications and hormone treatments for the fertility of dairy cows.
      ).
      Heat stress has been associated with reductions in DMI (
      • Spiers D.E.
      • Spain J.N.
      • Sampson J.D.
      • Rhoads R.P.
      Use of physiological parameters to predict milk yield and feed intake in heat-stressed dairy cows.
      ;
      • Bernabucci U.
      • Lacetera N.
      • Baumgard L.H.
      • Rhoads R.P.
      • Ronchi B.
      • Nardone A.
      Metabolic and hormonal acclimation to heat stress in domesticated ruminants.
      ;
      • Soriani N.
      • Panella G.
      • Calamari L.
      Rumination time during the summer season and its relationships with metabolic conditions and milk production.
      ) and feeding bouts (
      • Bernabucci U.
      • Lacetera N.
      • Baumgard L.H.
      • Rhoads R.P.
      • Ronchi B.
      • Nardone A.
      Metabolic and hormonal acclimation to heat stress in domesticated ruminants.
      ), consequently affecting rumination (
      • Kadzere C.T.
      • Murphy M.R.
      • Silanikove N.
      • Maltz E.
      Heat stress in lactating dairy cows: A review.
      ;
      • Bernabucci U.
      • Lacetera N.
      • Baumgard L.H.
      • Rhoads R.P.
      • Ronchi B.
      • Nardone A.
      Metabolic and hormonal acclimation to heat stress in domesticated ruminants.
      ;
      • Soriani N.
      • Panella G.
      • Calamari L.
      Rumination time during the summer season and its relationships with metabolic conditions and milk production.
      ). This can have consequences for rumen pH because more feeding bouts and ruminating produce saliva, which acts as a pH buffer and is important for healthy rumen pH (
      • Bernabucci U.
      • Lacetera N.
      • Baumgard L.H.
      • Rhoads R.P.
      • Ronchi B.
      • Nardone A.
      Metabolic and hormonal acclimation to heat stress in domesticated ruminants.
      ). Heat stress also affects cow behavior, including preference for standing rather than lying (
      • Tucker C.B.
      • Rogers A.R.
      • Schütz K.E.
      Effect of solar radiation on dairy cattle behaviour, use of shade and body temperature in a pasture-based system.
      ;
      • Allen J.D.
      • Hall L.W.
      • Collier R.J.
      • Smith J.F.
      Effect of core body temperature, time of day, and climate conditions on behavioral patterns of lactating dairy cows experiencing mild to moderate heat stress.
      ), even after lying deprivation (
      • Schütz K.E.
      • Cox N.R.
      • Matthews L.R.
      How important is shade to dairy cattle? Choice between shade or lying following different levels of lying deprivation.
      ), which is a welfare issue. The increase of maintenance metabolism (
      • Collier R.J.
      • Beede D.
      • Thatcher W.
      • Israel L.
      • Wilcox C.
      Influences of environment and its modification on dairy animal health and production.
      ) and reduction in DMI (
      • Spiers D.E.
      • Spain J.N.
      • Sampson J.D.
      • Rhoads R.P.
      Use of physiological parameters to predict milk yield and feed intake in heat-stressed dairy cows.
      ;
      • Bernabucci U.
      • Lacetera N.
      • Baumgard L.H.
      • Rhoads R.P.
      • Ronchi B.
      • Nardone A.
      Metabolic and hormonal acclimation to heat stress in domesticated ruminants.
      ;
      • Soriani N.
      • Panella G.
      • Calamari L.
      Rumination time during the summer season and its relationships with metabolic conditions and milk production.
      ) during heat stress result in cows often being in a state of negative energy balance (
      • Drackley J.K.
      Biology of dairy cows during the transition period: The final frontier?.
      ). Negative energy balance subsequently diminishes milk production (
      • Spiers D.E.
      • Spain J.N.
      • Sampson J.D.
      • Rhoads R.P.
      Use of physiological parameters to predict milk yield and feed intake in heat-stressed dairy cows.
      ;
      • Soriani N.
      • Panella G.
      • Calamari L.
      Rumination time during the summer season and its relationships with metabolic conditions and milk production.
      )—the primary source of income to dairy producers—and is therefore a serious economic issue for the dairy industry.
      It is important to investigate options for cooling heat-stressed dairy cows to improve milk production to support dairy farm economics and to improve cow welfare during periods of heat stress. Options for heat abatement have previously included the use of shade, fans, and soaking the cows, which typically reduce the negative effects of heat stress on physiology and behavior (
      • Schütz K.E.
      • Rogers A.
      • Cox N.
      • Webster J.
      • Tucker C.
      Dairy cattle prefer shade over sprinklers: Effects on behavior and physiology.
      ;
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Cooling cows efficiently with water spray: Behavioral, physiological, and production responses to sprinklers at the feed bunk.
      ;
      • Tresoldi G.
      • Schütz K.E.
      • Tucker C.B.
      Cooling cows with sprinklers: Spray duration affects physiological responses to heat load.
      ). For decades, one of the most efficient methods of cooling dairy cattle was based on repeated soaking to attain maximal water trapping in the coat, followed by its rapid evaporation (
      • Flamenbaum I.
      • Wolfenson D.
      • Mamen M.
      • Berman A.
      Cooling dairy cattle by a combination of sprinkling and forced ventilation and its implementation in the shelter system.
      ;
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Cooling cows efficiently with water spray: Behavioral, physiological, and production responses to sprinklers at the feed bunk.
      ). Water as a method of cooling is often delivered via automated cycling sprinklers installed above feed alleys; however, cows may perceive them as a deterrent or obstacle, because wetting their head is uncomfortable (
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Cooling cows efficiently with water spray: Behavioral, physiological, and production responses to sprinklers at the feed bunk.
      ). Conversely, cows have not been observed to display head-wetting avoidance behavior in a voluntary use soaking system (
      • Legrand A.
      • Schütz K.E.
      • Tucker C.B.
      Using water to cool cattle: Behavioral and physiological changes associated with voluntary use of cow showers.
      ).
      Many cooling strategies are used to keep cows in thermal homeostasis; however, most of them are applied to the group level, at the feed bunk or milking parlor (
      • Becker C.A.
      • Stone A.E.
      Graduate student literature review: Heat abatement strategies used to reduce negative effects of heat stress in dairy cows.
      ). Providing cows with longer soaking sessions in a holding pen (20 to 140 min) has been shown to be effective in aiding cows in reducing and maintaining lower body temperatures (
      • Araki C.T.
      • Nakamura R.M.
      • Kam L.W.G.
      • Clarke N.L.
      Diurnal temperature patterns of early lactating cows with milking parlor cooling.
      ;
      • Flamenbaum I.
      • Wolfenson D.
      • Mamen M.
      • Berman A.
      Cooling dairy cattle by a combination of sprinkling and forced ventilation and its implementation in the shelter system.
      ;
      • Valtorta S.E.
      • Gallardo M.R.
      Evaporative cooling for Holstein dairy cows under grazing conditions.
      ;
      • Kendall P.E.
      • Verkerk G.
      • Webster J.
      • Tucker C.
      Sprinklers and shade cool cows and reduce insect-avoidance behavior in pasture-based dairy systems.
      ).
      Although it may not be the most common heat abatement practice, producers will opt to provide cows with a short soaking at the exit of the milking parlor (
      • Van Os J.M.
      Considerations for cooling dairy cows with water.
      ). Limited research is available on the benefits of soaking cows at the exit of the milking parlor, yet
      • Collier R.J.
      • Dahl G.E.
      • VanBaale M.J.
      Major advances associated with environmental effects on dairy cattle.
      stated that providing cows soakings at the exit of the milking parlor can provide animals with an extra 15 to 25 min of additional cooling, depending on the weather conditions. Hence, there is a need to investigate further the validity and effects of the adoption of short soaking cycles at the exit of the milking parlor, and whether this practice is beneficial when paired with other heat abatement practices.
      Dairy cattle differ in how they respond to an increase in heat load. Voluntary soaking stations for heat stress abatement provide freedom of choice and cow self-management, which focuses on individual cow needs instead of the group. Other voluntary use equipment (e.g., automatic milking systems) is perceived as advantageous because it removes the necessity of daily laborious tasks (e.g., daily milking) and adds freedom of choice while avoiding herding and interaction with humans (
      • Webster A.J.
      Farm animal welfare: The five freedoms and the free market.
      ;
      • Holloway L.
      • Bear C.
      • Wilkinson K.
      Re-capturing bovine life: Robot–cow relationships, freedom and control in dairy farming.
      ). Because individual cows have different tolerances to heat stress, it seems logical to offer heat abatement at an individually self-managed level, such as by a voluntary use soaker station. Cow heat tolerance differs among individuals because of genetics (
      • Aguilar I.
      • Misztal I.
      • Tsuruta S.
      Genetic components of heat stress for dairy cattle with multiple lactations.
      ;
      • Liang D.
      • Wood C.L.
      • McQuerry K.J.
      • Ray D.L.
      • Clark J.D.
      • Bewley J.M.
      Influence of breed, milk production, season, and ambient temperature on dairy cow reticulorumen temperature.
      ;
      • Alfonzo E.P.M.
      • da Silva M.V.G.B.
      • dos Santos Daltro D.
      • Stumpf M.T.
      • Dalcin V.C.
      • Kolling G.
      • Fischer V.
      • McManus C.M.
      Relationship between physical attributes and heat stress in dairy cattle from different genetic groups.
      ), parity (
      • Aguilar I.
      • Misztal I.
      • Tsuruta S.
      Genetic components of heat stress for dairy cattle with multiple lactations.
      ;
      • Stone A.E.
      • Jones B.W.
      • Becker C.A.
      • Bewley J.M.
      Influence of breed, milk yield, and temperature-humidity index on dairy cow lying time, neck activity, reticulorumen temperature, and rumination behavior.
      ), milk production (
      • Liang D.
      • Wood C.L.
      • McQuerry K.J.
      • Ray D.L.
      • Clark J.D.
      • Bewley J.M.
      Influence of breed, milk production, season, and ambient temperature on dairy cow reticulorumen temperature.
      ;
      • Stone A.E.
      • Jones B.W.
      • Becker C.A.
      • Bewley J.M.
      Influence of breed, milk yield, and temperature-humidity index on dairy cow lying time, neck activity, reticulorumen temperature, and rumination behavior.
      ), body size, hair structure (
      • Alfonzo E.P.M.
      • da Silva M.V.G.B.
      • dos Santos Daltro D.
      • Stumpf M.T.
      • Dalcin V.C.
      • Kolling G.
      • Fischer V.
      • McManus C.M.
      Relationship between physical attributes and heat stress in dairy cattle from different genetic groups.
      ), and a myriad of other factors.
      The variance of heat stress effects on animals are well known; however, with more individualized management in dairy farms, group cooling opportunities are becoming restricted. It is known that dairy cattle are variable in their responses to an increase in heat load. Thus, there is an opportunity to provide dairy cows with a voluntary heat stress abatement method that allows animals to self-manage their heat stress. Because animals may have different requirements and therefore motivations to use heat stress abatement tools, it would be beneficial to investigate whether there is a need to provide extra heat abatement strategies in addition to the use of voluntary heat abatement systems. Thus, the first objective of our study was to investigate the effect of 2 mandatory soakings at the exit of the milking parlor and free access to a voluntary soaker compared with cows with access to a voluntary soaker only, with no mandatory soakings. The second objective of this study was to assess the heat abatement capability of voluntary soaking of cows by assessing cow physiology (RR and body temperature), behavior (rumination, feeding, lying time, and steps per day), and milk production. Last, this study aimed to determine the individual use of the voluntary soaking system and its relationship with THI.

      MATERIALS AND METHODS

      Animal Housing and Diet

      The study was conducted from July 10 to October 3, 2018, at the University of Kentucky Coldstream Research Dairy Farm (Lexington, KY; latitude, 38.1103759; longitude, −84.5164302), and was approved by the Institutional Animal Care and Use Committee of the University of Kentucky (Protocol No. 2018-2914).
      Cows were housed in a compost-bedded pack barn that was tilled twice per day (at approximately 0520 and 1415 h). The experimental pen was equipped with a total of 8 automatic intake recording feeders (Insentec, Hokofarm Group), one 4.9-m low-speed high-volume fan (Powerfoil X3.0, Big Ass Fans) over the bedded pack area, and three 91-cm fans (Yellow Jacket, Big Ass Fans) over the feed alley. A motion-activated voluntary soaker (Cool Sense, Edstrom) was installed adjacent to the experimental pen as an extension of the feed alley walkway. The 20-m2 voluntary soaking area had a grooved concrete floor and was covered with a shade cloth that blocked 75% of the solar radiation. The experimental pen layout, approximate measurements of the compost-bedded pack barn, and fan placement are illustrated in Figure 1. Cows were housed in the experimental pen starting at enrollment and then returned to the main herd at the end of the data collection period. Cows were fed a TMR formulated according to NRC guidelines (
      • NRC
      Nutrient Requirements of Dairy Cattle.
      ) to meet or exceed the requirements of lactating dairy cows producing at least 39 kg of milk daily. Composition of the TMR as fed was 40.7% corn silage, 27.8% lactating cow grain mix, 23.6% alfalfa silage, 5.1% cotton seed, 1.8% alfalfa hay, and 1.0% mineral mix. Cows were fed ad libitum twice per day at approximately 0800 and 1400 h. Orts were removed daily before the morning feeding. Animals had ad libitum access to fresh water provided from a self-filling water trough located in the feeding alley. Milking occurred twice daily at 0730 and 1800 h.
      Figure thumbnail gr1
      Figure 1Experimental pen for dairy cattle (n = 15) consists of 155-m2 compost-bedded pack pen and a 50-m2 feed alley. Cows were enrolled with 2 heat alleviation treatments: 2 mandatory soakings per day (mandatory soakings) via the exit alley of the milking parlor with access to a voluntary soaker and no mandatory soakings per day (no mandatory soakings) with access to a voluntary soaker. The voluntary use soaker was located immediately adjacent to the feed alley of the pen in an area approximately 20 m2, with a grooved concrete surface and shade overhead. Circle annotated fans are attached to the roof of the barn and rotated air flow downward, toward the pack. Arrow annotated fans are mounted above the feed bunk headlocks, and air flow follows the arrow direction.
      Fifteen confirmed-pregnant, mid-lactation Holstein cows were chosen randomly from the herd for enrollment in this study and were moved to the experimental pen for a 2-d adaptation period. After the adaptation, a 4-wk training period with the voluntary soaker started. On the first day of the training period, cows were 233 ± 38 (mean ± SD) DIM, had a parity of 2 ± 1, weighed 673 ± 69 kg, and had a milk yield of 38.0 ± 5.4 kg/d.

      Experimental Design

      Cows were split into 7 pairs, balanced for parity, milk production, and body weight; 1 cow was unpaired. Cows were assigned within pairs to 1 of the 2 treatments by random block design for eight 1-wk treatments, totaling 8 wk of data collection per pair. The possible treatments were (1) the mandatory soaker treatment, which comprised 2 mandatory soakings/d with free access to the voluntary soaker; and (2) the no mandatory soaker treatment, which comprised no daily mandatory soakings with free access to the voluntary soaker. Mandatory soakings were given by sorting cows via a sort gate (AfiSort, Afimilk) after milking, and guiding them under a motion-activated cattle soaker (Cool Sense, Edstrom) located adjacent to the milking parlor. Cows had free access to the voluntary soaker adjacent to the experimental pen at any time except during milking or when the feeding alley was scraped (mean access ± SD, 18.3 ± 1.6 h/d).
      Cows were trained individually to use the voluntary soaker during the 4-wk training period. Training for the voluntary soaker involved a single experimenter encouraging cows to pass under the motion-activated soaker 3 times/d (at 1000, 1230, and 1500 h). Training was considered complete after a cow used the soaker voluntarily at 2 separate instances within 3 d (monitored via video footage). All cows enrolled were trained successfully to use the soaker. In addition to voluntary soaker training, cows were acclimated to the mandatory soaker during the 4-wk training period by using a sort gate to guide them under a motion-activated soaker at the exit alley from the milking parlor. After the 4-wk training period, the 8 wk of treatments were started.
      The mandatory and voluntary soakers were identical in model and setting. The soaking system is described in
      • Mazon G.
      • Montgomery P.D.
      • Hayes M.
      • Jackson J.
      • Costa J.H.C.
      Development and validation of an autonomous radio-frequency identification controlled soaking system for dairy cattle.
      . Briefly, both soakers were set to a 5-s cycle; the water flow rate was approximately 4.1 L/5-s soaker cycle (or 49.2 L/min) via 2 shower heads (accumulatively). The soaker system was activated after both motion sensors were triggered. The soaker at the exit alley was installed per manufacturer instructions. Two motion sensors were installed above the exit alley approximately 1.8 m apart to allow 1 cow to activate the soaker while walking through the alley (soaking only 1 cow at a time). However, the voluntary soaker was modified; both motion sensors were next to each other, immediately adjacent to the shower heads. This modification was made so a cow could activate both motion sensors (and therefore initiate a soaking cycle) while standing under the water flow.

      Data Collection

      Physiological measurements of the cows measured during the study were reticulorumen temperature (RT), RR, and panting score. Reticulorumen temperature measurements were collected with an automated data logging bolus (Herdstrong TruCore, DVM Systems), which was validated previously for recording of RT (
      • Bewley J.M.
      • Einstein M.
      • Grott M.
      • Schutz M.
      Comparison of reticular and rectal core body temperatures in lactating dairy cows.
      ). The bolus manufacturer supplied the researchers with RT data after removing temperature changes caused by water intake (
      • Cantor M.C.
      • Costa J.H.
      • Bewley J.M.
      Impact of observed and controlled water intake on reticulorumen temperature in lactating dairy cattle.
      ) using a proprietary algorithm. Boluses were assigned to cows 6 ± 1 d before the start of the training period.
      Two observers recorded RR and panting scores (observer 1, 88%; observer 2, 12% of the observations). High interobserver agreement was achieved for RR and panting score as defined by
      • Hinkle D.E.
      Applied Statistics for the Behavioral Sciences.
      (r = 0.98 and 0.87, P < 0.001; R2 = 0.96 and 0.75, P < 0.001; respectively), and no bias was observed using Bland–Altman plots (
      • Bland J.M.
      • Altman D.G.
      Calculating correlation coefficients with repeated observations: Part 1: Correlation within subjects.
      ,
      • Bland J.M.
      • Altman D.G.
      Calculating correlation coefficients with repeated observations: Part 2–Correlation between subjects.
      ). Respiration rate was recorded thrice per day at 0645, 1230, and 1720 h. Respiration rate was recorded by counting flank movements for 1 min according to the methodology of
      • Rhoads M.L.
      • Rhoads R.P.
      • VanBaale M.J.
      • Collier R.J.
      • Sanders S.R.
      • Weber W.J.
      • Crooker B.A.
      • Baumgard L.H.
      Effects of heat stress and plane of nutrition on lactating Holstein cows: I. Production, metabolism, and aspects of circulating somatotropin 1.
      and
      • Min L.
      • Cheng J.
      • Shi B.
      • Yang H.
      • Zheng N.
      • Wang J.
      Effects of heat stress on serum insulin, adipokines, AMP-activated protein kinase, and heat shock signal molecules in dairy cows.
      . The observer recording RR was stationed approximately 5 m from the focal cow and ensured flank movements were visible for the duration of the observation. At the same time, panting score was recorded using a predefined ethogram (Table 1).
      Table 1Microclimate conditions (daily mean, SD, and daily minimum and daily maximum) of experimental pen
      Daily environmental conditions calculated from 0000 to 2359 h each day during the treatment period. THI = temperature-humidity index.
      VariableDaily (24 h)
      MeanSDMinimumMaximum
      Temperature
      Measurements taken from inside the experimental cows' home pen.
      (°C)
      23.53.215.328.0
      Relative humidity
      Measurements taken from inside the experimental cows' home pen.
      (%)
      71.76.245.081.3
      Precipitation
      Measurements obtained from the University of Kentucky Agronomy Research Farm (latitude, 38.1341919; longitude, −84.4962154).
      (mm)
      8.116.50.071.1
      Wind speed
      Measurements taken from inside the experimental cows' home pen.
      (m/s)
      0.30.40.01.9
      THI71.94.959.478.6
      1 Daily environmental conditions calculated from 0000 to 2359 h each day during the treatment period. THI = temperature-humidity index.
      2 Measurements taken from inside the experimental cows' home pen.
      3 Measurements obtained from the University of Kentucky Agronomy Research Farm (latitude, 38.1341919; longitude, −84.4962154).
      Rumination (min/d) and feeding (min/d) were recorded for each cow by a behavior-monitoring collar (MooMonitor+, DairyMaster). The collar was validated previously for all the used behaviors (
      • Grinter L.N.
      • Campler M.R.
      • Costa J.H.C.
      Technical note: Validation of a behavior monitoring collar's precision and accuracy to measure rumination, feeding, and resting time of lactating dairy cattle.
      ). Collars were assigned to cows per farm protocol (306 ± 197 d before the beginning of the training period). A behavior-monitoring leg tag (AfiTagII, Afimilk) was used to monitor lying time (min/d), lying bouts (bouts/d), and steps (steps/d). The leg tag was validated previously for lying time, lying bouts, and steps (
      • Higginson J.H.
      • Millman S.T.
      • Leslie K.E.
      • Kelton D.F.
      Validation of a new pedometry system for use in behavioural research and lameness detection in dairy cattle.
      ). Leg tags were assigned to cows per farm protocol (>30 d before the start of the training period).
      Daily milk yield was recorded during each milking and was summarized by day using an automatic meter (AfiMilk, AfiMilk). Milk fat and protein were measured at each milking using an in-line milk analyzer (AfiLab, AfiMilk) that was validated previously (
      • Kaniyamattam K.
      • De Vries A.
      Agreement between milk fat, protein, and lactose observations collected from the Dairy Herd Improvement Association (DHIA) and a real-time milk analyzer.
      ). A 3-d rolling average was calculated each day for milk yield, milk fat, and milk protein by taking the mean value of a day with the previous 2 d.
      Use of the voluntary soaker was monitored 24 h/d for the duration of the study via video footage (Hikvision model DS-2CD2342Wd-I, Hangzhou Hikvision Digital Technology Co. Ltd.). Video was recorded and later played back to record soaker use by each animal and the part of the body targeted for soaking. Four observers recorded voluntary soaker use. When soaker use was detected, the observers recorded the cow identification number, time of cycle activation (hh:mm:ss), and area of cow under the soaker according to an ethogram (Table 2). In addition, at the end of each soaking cycle, observers recorded whether the cow continued using the soaker, was displaced (by another cow or farm personnel), stopped using the soaker voluntarily (no other cows present), or stopped using the soaker for an unknown reason (not obvious whether displacement occurred or the cow chose to exit). In any event of displacement, the cow displacing and the cow that was displaced were both recorded. Voluntary soaker use was summed by experimental day (0000 to 2359 h) and averaged by hour for each and all animals during the experimental period. To determine interobserver reliability, fifteen 1-h blocks of video were watched simultaneously by all observers to determine the use of the soaker by each cow during the period. Very high correlations (r > 0.95) and very high linear regressions (R2 > 0.95) were used to deem observer reliability for discerning soaker use per day.
      Table 2Ethogram followed to define panting
      Panting score was recorded live at the same time respiration rate was taken, 3 times/d—before morning milking, midday, and before evening milking—during the treatments. Heat alleviation treatments were 2 mandatory soakings daily via the exit alley of the milking parlor with access to a voluntary soaker, and no mandatory soakings per day with access to a voluntary soaker. For each panting score observation, observers were stationed approximately 5 m from the focal cow and ensured flank movements were visible for the duration of the observation.
      Breathing behaviorApproximate respiration rate (breaths/min)Panting score
      No panting, normal. Difficult to see chest movement.<400
      Slight panting, mouth closed, no drool or foam. Easy to see chest movement.40–701
      Fast panting, drool or foam present. No open-mouth panting.70–1202
      Fast panting, drool or foam present. Occasional open mouth; tongue not extended.70–1202.5
      Open mouth and some drool present. Neck extended; head may be up.120–1603
      Open mouth and excessive drooling. Tongue out slightly, occasionally fully extended for short periods. Neck extended and head usually up.120–1603.5
      Open mouth with tongue fully extended for prolonged periods and excessive drooling. Neck extended and head up.>1604
      Open mouth with tongue fully extended for prolonged periods. Head held down, drooling may cease. Cattle “breathe” from flank.Variable (may decrease)4.5
      1 Panting score was recorded live at the same time respiration rate was taken, 3 times/d—before morning milking, midday, and before evening milking—during the treatments. Heat alleviation treatments were 2 mandatory soakings daily via the exit alley of the milking parlor with access to a voluntary soaker, and no mandatory soakings per day with access to a voluntary soaker. For each panting score observation, observers were stationed approximately 5 m from the focal cow and ensured flank movements were visible for the duration of the observation.
      Ambient temperature and relative humidity (RH) were recorded by a portable weather station (HOBO External Temperature/Relative Humidity Data Logger model U23-002, Onset Computer Corp.) located in the study pen. Wind speed was recorded by an anemometer (Digi-Sense model 20250-22, Cole-Parmer) located in the study pen. The calculations for THI include air temperature (T) and RH, were performed using the following equation: THI = (1.8 × T + 32) – (0.55 – 0.0055 × RH) × (1.8 × T – 26), where T is the ambient temperature in degrees Celsius and RH is the percentage of relative humidity (

      National Oceanic and Atmospheric Administration. 1976. Livestock Hot Weather Stress. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service Central Region, Regional Operations Manual Letter C-31-76.

      ).
      Hourly THI weather values were averaged to calculate mean daily THI, and the maximum daily value was taken for the daily maximum THI. In addition, mean daily THI was averaged by hour for the duration of the experimental study to calculate the mean hourly THI. Wind speed data were calculated on a mean daily basis. Daily precipitation data were collected from the University of Kentucky Agronomy Research Farm (latitude, 38.1341919; longitude, −84.4962154; approximately 4.8 km from the University of Kentucky Coldstream Research Dairy Farm) and summed by day. A summary of environmental conditions during the experimental period is given in Table 3.
      Table 3Ethogram used by observers for recording area of cow wet by soaker when recording voluntary soaker use at the pen
      Recording of soaker use was made by observing daily video recordings (24 h/d) of the soaker area for the duration of the experimental period.
      Area wetDefinition
      RumpCow wet anywhere between (and including) rump and hip bones.
      Neck and headCow wet anywhere between (and including) shoulders and end of nose.
      BackCow wet between hip and shoulder bones, or if cow is in motion and wets a combination of rump, neck and head, and back areas.
      SideCow wets any area but only on one side (water does not spill over spine to other side).
      LickingCow only licks water, and water does not wet the head.
      1 Recording of soaker use was made by observing daily video recordings (24 h/d) of the soaker area for the duration of the experimental period.

      Statistical Analysis

      All statistical analyses were performed using SAS (version 9.4, SAS Institute Inc.). Before analysis, all data were checked for normality using the UNIVARIATE procedure probability distribution plots. For daily lying time, values equal to 0 min/d or greater than 1,440 min/d were removed because they were considered recording errors by the device. The first (<366 min) and 99th (>1,014 min) percentiles of data were also removed (
      • Stone A.E.
      • Jones B.W.
      • Becker C.A.
      • Bewley J.M.
      Influence of breed, milk yield, and temperature-humidity index on dairy cow lying time, neck activity, reticulorumen temperature, and rumination behavior.
      ). Seven percent of lying bouts data was removed because the device reported 0 lying bout/d, which was considered a recording error.
      Originally there were 28,498 recordings for RT. Any hour when the mean RT was <35.6°C or >42.2°C was removed for biological relevance, as outlined by
      • Bewley J.M.
      • Einstein M.
      • Grott M.
      • Schutz M.
      Comparison of reticular and rectal core body temperatures in lactating dairy cows.
      . This step removed 8,654 data points. After this, an additional 190 were removed because they were deemed as outliers for exceeding 3 SD of the mean, according to the same data preparation steps as
      • Bewley J.M.
      • Einstein M.
      • Grott M.
      • Schutz M.
      Comparison of reticular and rectal core body temperatures in lactating dairy cows.
      , resulting in 19,654 points.
      Data from cows detected having mastitis (2 cows) or in estrus (1 cow) by standard farm procedures during the study were removed the day before detection, day of detection, and day after detection.
      The effect of soaker treatment was determined by ANOVA using mixed linear models (MIXED procedure). The model included treatment (mandatory soakings or no mandatory soakings), soaker use per day, pair, mean daily THI, DIM, daily milk yield (kg/d), and interaction of treatment with mean daily THI. Study day was specified as a repeated measure, and cow as the subject, using an autoregressive structure. Effects with a P-value >0.30 were removed from the model using a stepwise backward elimination process starting with the least contributing effect. Treatment, soaker use per day, pair, and mean daily THI remained in the model regardless of significance. Significance was declared at P ≤ 0.05, and trends were defined as P ≤ 0.10.
      When the fixed effects of voluntary soaker use per day or THI were significant for any outcome variable (RR, panting score, RT, rumination, feeding, lying, steps, milk yield, milk protein percentage, and milk fat percentage), an additional extraction of estimates was performed in the mixed models (ESTIMATE statement) for that variable. The relationship between the significant variables and voluntary soaker use per day and THI were classified as positive or negative.

      RESULTS

      Daily Soaker Use

      Treatment did not influence soaker use. The frequency of voluntary soaker use during the no mandatory soakings treatment was approximately 15 voluntary soakings/d, similar to the 2 mandatory soakings treatment of about 12 voluntary soakings/d (F1,14 = 1.74, P = 0.21; Table 4).
      Table 4Physiological, behavioral, and milk variables (mean ± SE) used to observe the heat abatement qualities of the 2 treatments between cows (n = 15)
      Treatments were (1) 2 mandatory soakings per day exiting the milking parlor with access to a voluntary soaker, and (2) no mandatory soakings per day with access to a voluntary soaker located immediately adjacent to the feed alley of the pen.
      VariableNo mandatory soakingsMandatory soakingsSEMP-value
      Soaker use14.812.41.40.21
      Respiration rate (breaths/min)
       Minimum42.944.00.500.13
       Mean56.457.30.410.09
       Maximum67.567.70.520.81
      Panting score
      Panting score was recorded 3 times/d utilizing a scale that ranged from 0 (no panting, normal) to 4.5 (severe panting, with animal displaying open mouth with tongue fully extended for prolonged periods, head held down, and intense flank movements).
       Minimum0.590.610.020.51
       Mean1.051.080.020.09
       Maximum1.481.500.020.57
      Reticulorumen temperature (°C)
       Minimum daily39.0339.030.010.83
       Mean daily39.6039.580.010.16
       Maximum daily40.1240.080.020.11
      Rumination time (min/d)543.4558.65.2<0.01
      Feeding time (min/d)173.4174.25.90.74
      Lying time (min/d)661.3673.05.90.06
      Lying bouts (bouts/d)10.811.00.160.28
      Steps (steps/d)2,113.62,172.450.00.28
      Milk
       Yield (kg/d)36.236.50.60.64
       Protein (%)2.952.940.020.35
       Fat (%)3.893.870.020.15
      1 Treatments were (1) 2 mandatory soakings per day exiting the milking parlor with access to a voluntary soaker, and (2) no mandatory soakings per day with access to a voluntary soaker located immediately adjacent to the feed alley of the pen.
      2 Panting score was recorded 3 times/d utilizing a scale that ranged from 0 (no panting, normal) to 4.5 (severe panting, with animal displaying open mouth with tongue fully extended for prolonged periods, head held down, and intense flank movements).
      There was large individual variation in voluntary soaker use, ranging from 0 to 227 soakings/d (mean ± SD, 13 ± 30 voluntary soakings/d) (Figure 2). Four cows had a maximum use of less than 10 soakings/d, whereas 4 other cows had a maximum of more than 100 soakings/d (Figure 2). Cows preferred to use the soaker predominantly on their back, followed by their side, rump, and neck and head, and licking was the least common soaker use area (Figure 3). At the end of each 5-s soaker cycle, cows typically continued to use the soaker (Figure 4). Cows were least likely to leave the soaker because of displacement (by cow or farm personnel), followed by leaving by choice (Figure 4). The main reason cows left the soaker was “unknown” (when the observer was unable to differentiate between leaving by choice versus a displacement; Figure 4). Cows with a greater frequency of soaker use were more likely to displace another cow from the soaker (F1,14 = 9.28, P < 0.01; Figure 5) or be displaced from the soaker (F1,14 = 30.61, P < 0.001; Figure 5). Soaker use peaked between 1900 and 2000 h, and the nadir (excluding hours manipulated by limited access) was between 1100 and 1200 h (Figure 6).
      Figure thumbnail gr2
      Figure 2Individual total daily frequency of voluntary soaker use (in 5-s cycles) assessed by 24-h video recording of dairy cattle (n = 15) enrolled with 2 individualized cooling strategy treatments. Treatments were (1) 2 mandatory soakings per day exiting the milking parlor with access to a voluntary soaker, and (2) no mandatory soakings per day with access to a voluntary soaker located immediately adjacent to the feed alley of the pen. In each boxplot, the center line represents the median for each cow, the whiskers represent the interquartile range of each cow, and the dots represent individual observations for each cow.
      Figure thumbnail gr3
      Figure 3Percentage of soaked areas of the cow from the voluntary soaker (x-axis) during the experimental period (8 wk, from August to October, in Lexington, KY) assessed by 24-h video recording. Treatments were 2 mandatory soakings per day exiting the milking parlor with access to a voluntary soaker, and no mandatory soakings per day with access to a voluntary soaker located immediately adjacent to the feed alley of the pen. In each boxplot, the center line represents the median for each soaked area, and the dots represent each cow's (n = 15) percentage of time soaking the corresponding area.
      Figure thumbnail gr4
      Figure 4Behaviors recorded at the end of each 5-s soaking cycle. Each point represents the percentage of time each cow (n = 15) performed the corresponding behavior. If cows “continued use,” the soaker was activated again for another cycle. Leaving the soaker area because of being displaced is indicated as displaced by farm personnel [Displaced (p)] or displaced by another cow [Displaced (c)]. A cow that left by “own choice” left with no other cows in the vicinity of the soaker to influence choice for leaving. An “unknown” reason was recorded when the observer was unable to attribute displacement or cow's own choice. In each boxplot, the center line represents the median for each cow, the whiskers represent the interquartile range of each cow, and the dots represent individual observations for each cow.
      Figure thumbnail gr5
      Figure 5Mean displacement actions of cows (n = 15) for the voluntary soaker, by cow (left y-axis). Depicted is the number of times a cow displaced another cow (diagonal striped bars) or a cow was displaced by another cow (horizontal striped bars). In addition, mean soaker use is displayed by the scatter graph (right y-axis). Displacements and soaker use were recorded by 24-h surveillance of the soaker.
      Figure thumbnail gr6
      Figure 6Mean hourly soaker use by cows (n = 15) as recorded from 24-h video recording (solid bars; left axis) with temperature-humidity index (THI; line graph; right axis). Mean daily THI is depicted by the dotted line with circles, and mean daily THI + 5-h delay is depicted by the dotted line with squares. Mean daily THI + 5-h delay was found to be the best predictor of mean hourly soaker use by the regression analysis (P < 0.01). Treatments were 2 mandatory soakings per day exiting the milking parlor with access to a voluntary soaker, and no mandatory soakings per day with access to a voluntary soaker located immediately adjacent to the feed alley of the pen. No effects of treatment were found; therefore, all data are presented. Cows were unable to access the soaker for approximately 5.7 ± 1.6 h/d. Soaker use was affected by being locked in the pen for other cows to milk (approximately 0600 to 0730 h and 1645 to 1750 h), leaving the pen for milking (approximately 0720 to 0740 h and 1750 to 1820 h), and leaving the pen while the alley was being scraped (approximately 0430 to 0510 h and 1500 to 1550 h).

      Respiration Rate and Panting Scores

      Treatment did not affect the minimum (F1,14 = 2.65, P = 0.13), mean (F1,14 = 3.29, P = 0.09), or maximum (F1,14 = 0.06, P = 0.81) RR (Table 4). Soaker use did affect the RR minimum (F1,752 = 5.51, P = 0.02); therefore, the estimates were analyzed, showing a positive relationship between soaker use and RR minimum (Table 5). However, no difference in soaker use and mean RR (F1,736 = 0.97, P = 0.33) or maximum RR (F1,751 = 0.11, P = 0.74) was noted.
      Table 5Results of physiological, behavioral, and milk variables for cows (n = 15) with the fixed effects of soaker use per day and temperature-humidity index from the mixed linear model
      If the result was significant from this model, an estimate was extracted from the mixed model for the response variables with mean daily temperature-humidity index and soaker use per day; associations were classified as positive or negative. Treatments were (1) 2 mandatory soakings per day exiting the milking parlor with access to a voluntary soaker, and (2) no mandatory soakings per day with access to a voluntary soaker located immediately adjacent to the feed alley of the pen. No effects of treatment found; therefore, all data are presented.
      VariableSoaker use per dayTemperature-humidity index
      P-valueRelationshipP-valueRelationship
      Soaker use per day<0.001Positive
      Respiration rate (breaths/min)
       Minimum0.02Positive<0.001Positive
       Mean0.33NS<0.001Positive
       Maximum0.74NS<0.001Positive
      Panting score
      Panting score was recorded 3 times/d utilizing a scale that ranged from 0 (no panting, normal) to 4.5 (severe panting, with animal displaying open mouth with tongue fully extended for prolonged periods, head held down, and intense flank movements).
       Minimum0.58NS<0.001Positive
       Mean0.49NS<0.001Positive
       Maximum0.63NS<0.001Positive
      Reticulorumen temperature (°C)
       Minimum daily0.12NS<0.001Positive
       Mean daily<0.001Positive<0.001Positive
       Maximum daily<0.001Positive<0.001Positive
      Rumination time (min/d)<0.001Negative<0.001Negative
      Feeding time (min/d)0.94NS<0.001Negative
      Lying time (min/d)0.25NS<0.001Negative
      Lying bouts (bouts/d)0.70NS<0.01Positive
      Steps (steps/d)<0.001Positive<0.001Positive
      Milk
       Yield (kg/d)0.02Positive<0.001Positive
       Protein (%)0.95NS0.72NS
       Fat (%)0.90NS<0.001Negative
      1 If the result was significant from this model, an estimate was extracted from the mixed model for the response variables with mean daily temperature-humidity index and soaker use per day; associations were classified as positive or negative. Treatments were (1) 2 mandatory soakings per day exiting the milking parlor with access to a voluntary soaker, and (2) no mandatory soakings per day with access to a voluntary soaker located immediately adjacent to the feed alley of the pen. No effects of treatment found; therefore, all data are presented.
      2 Panting score was recorded 3 times/d utilizing a scale that ranged from 0 (no panting, normal) to 4.5 (severe panting, with animal displaying open mouth with tongue fully extended for prolonged periods, head held down, and intense flank movements).
      Treatment did not affect the minimum (F1,14 = 0.45, P = 0.51), mean (F1,14 = 3.36, P = 0.09), or maximum (F1,14 = 0.34, P = 0.57) panting score (Table 4). Soaker use did not affect the panting score minimum (F1,696 = 0.31, P = 0.58), mean (F1,736 = 0.47, P = 0.49), or maximum (F1,751 = 0.24, P = 0.63).

      Reticulorumen Temperature

      Treatment did not affect the minimum (F1,14 = 0.05, P = 0.83), mean (F1,14 = 2.20, P = 0.16), or maximum (F1,14 = 2.99, P = 0.11) RT (Table 4). Soaker use did not affect RT minimum (F1,637 = 2.38, P = 0.12), but the mean (F1,637 = 19.37, P < 0.001) and maximum RT (F1,637 = 25.62, P < 0.001) were related positively to increases in voluntary soaker use (Table 5).

      Feeding Behavior

      Cows ruminated for more minutes per day during the 2 mandatory soakings treatment (558.6 ± 5.2 min/d) when compared with the no mandatory soakings treatment (543.4 ± 5.2 min/d, F1,14 = 11.14, P < 0.01; Table 4). In addition, there was a negative relationship with daily rumination and daily soaker use (F1,752 = 11.28, P < 0.001; Table 5). Treatment did not affect daily feeding time (F1,14 = 0.12, P = 0.74), nor did daily soaker use affect daily feeding time (F1,752 = 0.01, P = 0.94; Table 5).

      Lying Time, Lying Bouts, and Steps

      The 2 mandatory soakings treatment tended to result in longer daily lying time than the no mandatory soakings treatment (mandatory soakings, 673.0 ± 5.9 min/d; no mandatory soakings, 661.3 ± 5.9 min/d; F1,13 = 4.3; P = 0.06); however, lying bouts were not affected by treatment (F1,13 = 1.25, P = 0.28; Table 4). There was no relationship between daily lying time (F1,682 = 5.08, P = 0.25) or daily lying bouts (F1,641 = 0.15, P = 0.70) and daily soaker use (Table 5). The number of daily steps was not affected by treatment (F1,13 = 1.30, P = 0.28; Table 4). However, the number of steps increased with increasing voluntary soaker use per day (F1,416 = 17.46, P < 0.001; Table 5).

      Milk Production

      The milk yield (F1,14 = 0.23, P = 0.64), milk protein percentage (F1,14 = 0.95, P = 0.35), and milk fat (F1,14 = 2.36, P = 0.15) were not affected by treatment. There was a positive relationship between milk yield and soaker use per day as higher yielding cows visited the voluntary soaker more frequently (F1,698 = 5.93, P = 0.02; Table 5). No relationships between soaker use and milk protein percentage (F1,751 = 0.00, P = 0.95) or milk fat (F1,750 = 0.01, P = 0.90) were seen (Table 5).

      Temperature-Humidity Index

      Temperature-humidity index affected physiological and behavioral variables, and almost all milk-related variables in the mixed model (Table 5). The relationship and its direction between the response variables with daily soakings and THI are given in Table 5. In summary, rumination, feeding and lying times, and milk fat percentage had a negative relationship with THI. Voluntary soaker use (Figure 7) and all other significant variables had a positive relationship with THI.
      Figure thumbnail gr7
      Figure 7Daily voluntary soaker use (y-axis) depicted against the respective day's mean daily temperature-humidity index (THI; x-axis). Values for each cow's (n = 15) daily soaker use are represented by different symbols. Daily soaker use was recorded by 24-h surveillance of the soaker. Treatments were 2 mandatory soakings per day exiting the milking parlor with access to a voluntary soaker, and no mandatory soakings per day with access to a voluntary soaker located immediately adjacent to the feed alley of the pen.

      DISCUSSION

      Voluntary soaking opportunities were provided to dairy cows during a time of elevated THI. This study is the first to compare the use of a voluntary soaker method with or without a mandatory cooling opportunity for dairy cows, in combination with provision of fans and shade. We found limited differences in heat stress alleviation between the 2 treatments of 2 mandatory soakings at the exit of the milking parlor with voluntary soaker use and no mandatory soakings with voluntary soaker use. We did not find an additional heat abatement between treatments nor within any physiological variables measured, including RR associated with heat stress (
      • Rhoads M.L.
      • Rhoads R.P.
      • VanBaale M.J.
      • Collier R.J.
      • Sanders S.R.
      • Weber W.J.
      • Crooker B.A.
      • Baumgard L.H.
      Effects of heat stress and plane of nutrition on lactating Holstein cows: I. Production, metabolism, and aspects of circulating somatotropin 1.
      ;
      • Schütz K.E.
      • Rogers A.
      • Poulouin Y.
      • Cox N.
      • Tucker C.
      The amount of shade influences the behavior and physiology of dairy cattle.
      ;
      • Min L.
      • Cheng J.
      • Shi B.
      • Yang H.
      • Zheng N.
      • Wang J.
      Effects of heat stress on serum insulin, adipokines, AMP-activated protein kinase, and heat shock signal molecules in dairy cows.
      ).
      The only behavioral variable affected by treatment was rumination time. Shorter daily rumination time has been suggested as being an indication of heat stress (
      • Kadzere C.T.
      • Murphy M.R.
      • Silanikove N.
      • Maltz E.
      Heat stress in lactating dairy cows: A review.
      ;
      • Bernabucci U.
      • Lacetera N.
      • Baumgard L.H.
      • Rhoads R.P.
      • Ronchi B.
      • Nardone A.
      Metabolic and hormonal acclimation to heat stress in domesticated ruminants.
      ;
      • Soriani N.
      • Panella G.
      • Calamari L.
      Rumination time during the summer season and its relationships with metabolic conditions and milk production.
      ;
      • Müschner-Siemens T.
      • Hoffmann G.
      • Ammon C.
      • Amon T.
      Daily rumination time of lactating dairy cows under heat stress conditions.
      ) and was observed in the nonmandatory soaking treatment in comparison to longer daily rumination time in the compulsory soaking treatment. In addition to the difference in rumination time between treatments, there was a positive relationship between soaker use and rumination time. Because rumination had a negative relationship with THI (reducing daily rumination time with increasing THI), the positive relationship between the mandatory soaking treatment and rumination time may suggest that soaker use mitigated, to some extent, the negative effects of heat stress on rumination. However, because there were no differences between treatments for RR, panting score, RT, daily feeding time, daily lying time or bouts, steps per day, or milk production and components, the results suggest cows assigned either treatment had a comparable level of heat alleviation. Cows in our study were highly productive, at more than 38 kg/d of yield, and, at this production level and with the high THI during the study, we found no differences between soaking treatments. As a limitation of this study, we did not have a true negative control with no heat abatement to quantify the heat stress effects in milk yield. Future research could investigate the magnitude of heat alleviation of heat soakers for cows in dairies with different heat abatement strategies (e.g., without fans, with sprinklers over the feed bunk, without shade) or include a treatment of no voluntary soaker.
      We did not observe any differences in the number of voluntary soakings between treatments. We believe that, regardless of treatment, cows were relatively cool. The minimum, mean, and maximum RT in our study were not at a level of concern for cattle in heat stress, as seen by
      • Lees A.M.
      • Lees J.C.
      • Lisle A.T.
      • Sullivan M.L.
      • Gaughan J.B.
      Effect of heat stress on rumen temperature of three breeds of cattle.
      in beef cattle and
      • Ammer S.
      • Lambertz C.
      • Gauly M.
      Comparison of different measuring methods for body temperature in lactating cows under different climatic conditions.
      in lactating dairy cows. The research on the use of mandatory soakings at the exit of the parlor is still limited, yet some producers will opt to provide cows a short soaking at the exit of the milking parlor (
      • Van Os J.M.
      Considerations for cooling dairy cows with water.
      ). Future research should investigate the possible benefits of soaking cows at the exit of the milking parlor as well as investigate the effects of heat stress on cows with access to a voluntary heat abatement system only.
      Although there was no difference in voluntary soaker use between treatments, it related positively to THI, as seen in previous studies that offered a voluntary soaker (
      • Legrand A.
      • Schütz K.E.
      • Tucker C.B.
      Using water to cool cattle: Behavioral and physiological changes associated with voluntary use of cow showers.
      ), voluntary sprinklers (
      • Parola F.
      • Hillmann E.
      • Schütz K.E.
      • Tucker C.B.
      Preferences for overhead sprinklers by naïve beef steers: Test of two nozzle types.
      ), or voluntary use of sprinklers over the feed bunk (
      • Parola F.
      • Hillmann E.
      • Schütz K.E.
      • Tucker C.B.
      Preferences for overhead sprinklers by naïve beef steers: Test of two nozzle types.
      ;
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Dairy cows use and prefer feed bunks fitted with sprinklers.
      2016). This suggests that cows may be more motivated to use a voluntary soaker during periods of elevated heat stress potential. However,
      • Parola F.
      • Hillmann E.
      • Schütz K.E.
      • Tucker C.B.
      Preferences for overhead sprinklers by naïve beef steers: Test of two nozzle types.
      and
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Dairy cows use and prefer feed bunks fitted with sprinklers.
      ,
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Cooling cows efficiently with water spray: Behavioral, physiological, and production responses to sprinklers at the feed bunk.
      used constantly running sprinklers (as opposed to the voluntary soaker in our study). Constantly running water without an escape route may be aversive to cows, because the animals would need to get their head wet, which has been associated with discomfort (
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Cooling cows efficiently with water spray: Behavioral, physiological, and production responses to sprinklers at the feed bunk.
      ). For instance, cows show head-wetting avoidance behaviors, such as a lowered head or keeping their head outside the sprinkler (
      • Kendall P.E.
      • Verkerk G.
      • Webster J.
      • Tucker C.
      Sprinklers and shade cool cows and reduce insect-avoidance behavior in pasture-based dairy systems.
      ;
      • Schütz K.E.
      • Rogers A.
      • Cox N.
      • Webster J.
      • Tucker C.
      Dairy cattle prefer shade over sprinklers: Effects on behavior and physiology.
      ;
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Cooling cows efficiently with water spray: Behavioral, physiological, and production responses to sprinklers at the feed bunk.
      ). Cows have also been observed standing with their head through headlocks when sprinklers over the feed bunk were activated, despite not feeding (
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Dairy cows use and prefer feed bunks fitted with sprinklers.
      ), and moving out of the sprinkler radius when sprinklers were activated (
      • Marcillac-Embertson N.M.
      • Robinson P.
      • Fadel J.
      • Mitloehner F.
      Effects of shade and sprinklers on performance, behavior, physiology, and the environment of heifers.
      ). In support of this work, we also found that cows wet their head and neck much less than other body areas when using the voluntary soaker. Conversely,
      • Legrand A.
      • Schütz K.E.
      • Tucker C.B.
      Using water to cool cattle: Behavioral and physiological changes associated with voluntary use of cow showers.
      found that cows had their head near the voluntary soaker heads for more than half the time when in the soaker. This difference in behavior may be a result of flow rate or water droplet size between the work of
      • Legrand A.
      • Schütz K.E.
      • Tucker C.B.
      Using water to cool cattle: Behavioral and physiological changes associated with voluntary use of cow showers.
      and our study.
      • Legrand A.
      • Schütz K.E.
      • Tucker C.B.
      Using water to cool cattle: Behavioral and physiological changes associated with voluntary use of cow showers.
      speculated this may be a result of cows having control over the water source (as opposed to sprinklers in
      • Schütz K.E.
      • Rogers A.
      • Cox N.
      • Webster J.
      • Tucker C.
      Dairy cattle prefer shade over sprinklers: Effects on behavior and physiology.
      and
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Dairy cows use and prefer feed bunks fitted with sprinklers.
      ,
      • Chen J.M.
      • Schütz K.E.
      • Tucker C.B.
      Cooling cows efficiently with water spray: Behavioral, physiological, and production responses to sprinklers at the feed bunk.
      , although this was not evident in our study. Future research should explore the motivation of cows to use a voluntary use soaker, or should experiment with different soaker structures (e.g., water flow, droplet size, design to avoid cow ears and head).
      High variability in voluntary soaker use among cows was observed in our study (ranging from 0 to 227 daily soaking cycles). Similarly,
      • Schütz K.E.
      • Rogers A.
      • Cox N.
      • Webster J.
      • Tucker C.
      Dairy cattle prefer shade over sprinklers: Effects on behavior and physiology.
      and
      • Legrand A.
      • Schütz K.E.
      • Tucker C.B.
      Using water to cool cattle: Behavioral and physiological changes associated with voluntary use of cow showers.
      found some cows did not seek further heat alleviation from a voluntary choice soaker.
      • Legrand A.
      • Schütz K.E.
      • Tucker C.B.
      Using water to cool cattle: Behavioral and physiological changes associated with voluntary use of cow showers.
      speculated that individual variation in soaker use may be related to a lack of learning of the cooling properties of water. However, in each of these studies, including our own, cows were previously accustomed to water. In addition, steers naive to sprinklers have been shown to use sprinklers for their cooling properties (
      • Parola F.
      • Hillmann E.
      • Schütz K.E.
      • Tucker C.B.
      Preferences for overhead sprinklers by naïve beef steers: Test of two nozzle types.
      ). The high variation in soaker use could also be because cows experience heat stress differently as a result of differences in genetics (
      • Aguilar I.
      • Misztal I.
      • Tsuruta S.
      Genetic components of heat stress for dairy cattle with multiple lactations.
      ;
      • Liang D.
      • Wood C.L.
      • McQuerry K.J.
      • Ray D.L.
      • Clark J.D.
      • Bewley J.M.
      Influence of breed, milk production, season, and ambient temperature on dairy cow reticulorumen temperature.
      ;
      • Alfonzo E.P.M.
      • da Silva M.V.G.B.
      • dos Santos Daltro D.
      • Stumpf M.T.
      • Dalcin V.C.
      • Kolling G.
      • Fischer V.
      • McManus C.M.
      Relationship between physical attributes and heat stress in dairy cattle from different genetic groups.
      ), milk variables (
      • Liang D.
      • Wood C.L.
      • McQuerry K.J.
      • Ray D.L.
      • Clark J.D.
      • Bewley J.M.
      Influence of breed, milk production, season, and ambient temperature on dairy cow reticulorumen temperature.
      ;
      • Macciotta N.P.P.
      • Biffani S.
      • Bernabucci U.
      • Lacetera N.
      • Vitali A.
      • Ajmone-Marsan P.
      • Nardone A.
      Derivation and genome-wide association study of a principal component-based measure of heat tolerance in dairy cattle.
      ;
      • Stone A.E.
      • Jones B.W.
      • Becker C.A.
      • Bewley J.M.
      Influence of breed, milk yield, and temperature-humidity index on dairy cow lying time, neck activity, reticulorumen temperature, and rumination behavior.
      ), body size, or hair structure (
      • Alfonzo E.P.M.
      • da Silva M.V.G.B.
      • dos Santos Daltro D.
      • Stumpf M.T.
      • Dalcin V.C.
      • Kolling G.
      • Fischer V.
      • McManus C.M.
      Relationship between physical attributes and heat stress in dairy cattle from different genetic groups.
      ). In our study, we attempted to account for such individual variation in heat stress tolerance (parity, milk yield), but we were unable to consider differences in genetics that may have contributed to voluntary soak use variability. Differences in genetics and therefore heat tolerance could be a reason for the high variation in daily soaker use. Voluntary cooling options provide cows with the choice of when to use the soaker and, importantly, whether they want to use the soaker at all. Yet, it is important to notice that assessing individual soaker use is labor intensive. Both our study and that of
      • Legrand A.
      • Schütz K.E.
      • Tucker C.B.
      Using water to cool cattle: Behavioral and physiological changes associated with voluntary use of cow showers.
      relied on manual review of video recordings to assess individual use of the voluntary soaking systems, which would not be feasible outside of a research setting. However, there are voluntary radiofrequency-controlled soaking systems that perform automatic identification of animals that activate the soaker (
      • Mazon G.
      • Montgomery P.D.
      • Hayes M.
      • Jackson J.
      • Costa J.H.C.
      Development and validation of an autonomous radio-frequency identification controlled soaking system for dairy cattle.
      ). This automatic identification would allow producers to identify easily those animals that are more prone to heat stress, and to provide early interventions that could benefit the entire herd. Therefore, a voluntary soaker may offer a good opportunity for heat-intolerant cows to alleviate heat stress.
      We suggest further research should investigate different voluntary cow soaker designs, individual motivation of cows for voluntary soakings, and the combination with other cooling strategies. Future research should also consider comparing cows with genetic testing for heat tolerance genes to investigate whether some cows that are less heat tolerant use the voluntary soaker or whether soaker use is related to individual preference.

      CONCLUSIONS

      This study found limited physiological and behavioral differences between the use of a voluntary soaker with or without 2 mandatory soakings. Rumination time only was longer in the treatment with 2 mandatory soakings. We conclude the results indicate similar heat alleviation between the treatments. However, voluntary soaker use related positively to THI. We encourage future research to investigate potential advantages of a voluntary soaker by comparing it to cows with no voluntary soaker, and different levels of heat abatement (such as with and without shade and fans) to explore heat abatement at the individual level further. In addition, future studies are necessary to understand cow preference to soaker or sprinkler designs to investigate why some cows prefer the soaker more than others.

      ACKNOWLEDGMENTS

      We gratefully acknowledge and thank the staff and students of the Coldstream Dairy Research Farm (Lexington, KY) who helped in this experiment, especially Adrien Lebreton, Charlotte Pertuisel, Brittany Core, Amelia Fendley, Joey Clark, and Matt Collins. We also thank Olga Vsevolozhskaya, Michelle Arnold, and Eric Vanzant from the University of Kentucky (Lexington, KY) for their contributions to this project. This project was funded by DairyMaster Co. (Kerry, Ireland) through a research project partnership with the Dairy Science Program at the University of Kentucky. This research was also funded in part by a U.S. Department of Agriculture National Institute of Food and Agriculture Hatch Grant Project (KY007100) at the University of Kentucky. The authors have not stated any conflicts of interest.

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