Thermodynamics of standing and lying behavior in lactating dairy cows in freestall and parlor holding pens during conditions of heat stress

Dietary supplementation of vitamin D3 and calcium partially recover the compromised time budget and circadian rhythm of lying behavior in lactating cows under heat stress

Heat stress (HS) impedes cattle behavior and performance and is an animal comfort and welfare issue. The objective of this study was to characterize the time budget and circadian rhythm of lying behavior in dairy cows during HS and to assess the effect of dietary supplementation of vitamin D3 and Ca. Twelve multiparous Holstein cows (42.2 ± 5.6 kg milk/d; 83 ± 27 d in milk) housed in tiestalls were used in a split-plot design with the concentration of dietary vitamin E and Se as main plots (LESe: 11.1 IU/kg and 0.55 mg/kg, and HESe: 223 IU/kg and 1.8 mg/kg, respectively). Within each plot cows were randomly assigned to (1) HS with low concentrations of vitamin D3 and Ca (HS, 1,012 IU/kg and 0.73%, respectively), (2) HS with high concentrations of vitamin D3 and Ca (HS+D3/Ca; 3,764 IU/kg and 0.97%, respectively), or (3) thermoneutral pair-fed (TNPF) with low concentrations of vitamin D3 and Ca (1,012 IU/kg and 0.73%, respectively) in a Latin square design with 14-d periods and 7-d washouts. Lying behavior was measured with HOBO Loggers in 15-min intervals. Overall, cows in HS spent less time lying per day relative to TNPF from d 7 to 14. Daily lying time was positively correlated with milk yield, energy-corrected milk yield, and feed efficiency, and was negatively correlated with rectal temperature, respiratory rate, fecal calprotectin, tumor necrosis factor-α, and C-reactive protein. A treatment by time interaction was observed for lying behavior: the time spent lying was lesser for cows in HS than in TNPF in the early morning (0000-0600 h) and in the night (1800-2400 h). The circadian rhythm of lying behavior was characterized by fitting a cosine function of time into linear mixed model. Daily rhythmicity of lying was detected for cows in TNPF and HS+D3/Ca, whereas only a tendency in HS cows was observed. Cows in TNPF had the highest mesor (the average level of diurnal fluctuations; 34.2 min/h) and amplitude (the distance between the peak and mesor; 17.9 min/h). Both the mesor and amplitude were higher in HS+D3/Ca relative to HS (26.6 vs. 25.2 min/h and 3.91 min/h vs. 2.18 min/h, respectively). The acrophase (time of the peak) of lying time in TNPF, HS, and HS+D3/Ca were 0028, 0152, and 0054 h, respectively. Lastly, a continuous increase in daily lying time in TNPF was observed during the first 4 d of the experimental period in which DMI was gradually restricted, suggesting that intake restrictions may shift feeding behavior and introduce biases in the behavior of animals. In conclusion, lying behavior was compromised in dairy cows under HS, characterizing reduced daily lying time and disrupted circadian rhythms, and the compromised lying behavior can be partially restored by supplementation of vitamin D3 and Ca. Further research may be required for a more suitable model to study behavior of cows under HS.

Effect of different air speeds at cow resting height in freestalls on heat stress responses and resting behavior in lactating cows in Wisconsin

Heat abatement (e.g., soakers, fans) effectively reduces the negative physiological and production effects of heat stress, but no previous studies have documented effective interventions for the reduced lying times observed in response to hot weather. Although likely adaptive for heat dissipation, the reduction in motivated lying behavior may be an animal welfare concern. We evaluated the effect of air speed from fans with variable frequency drives on the heat stress responses of cows in a naturally ventilated freestall barn. Eight groups of lactating Holsteins (16 cows/group) were exposed to 3 treatments in a replicated crossover design: control (fans off, 0.4 ± 0.2 m/s, measured 0.5 m above the stall surface to represent cow resting height) versus 60% (1.7 ± 0.5 m/s; ≥1 m/s in all stalls) and 100% (2.4 ± 0.8 m/s) fan power. Each treatment was applied for 3 d of acclimation and 4 d of data collection. The effects of treatment on daily maximum vaginal temperature (VT) and lying time (LT; both measured with data loggers), respiration rate (RR; recorded from video), unshaved scapular skin temperature (ST), milk yield (MY), and dry matter intake (DMI) were analyzed using linear mixed models. All models included the fixed effect of treatment and a repeated term for treatment day within group of cows, with group as the subject. The models for LT, VT, and RR also included a fixed effect for same-day temperature-humidity index (THI; recorded in the pens with data loggers) and the THI × treatment interaction. The models for DMI and MY, using data from the latter 3 d of each treatment period, also included a fixed effect for the previous day's THI and the -1 d THI × treatment interaction. Lying time differed among treatments (100% vs. 60% fan power vs. control: 14.2 vs. 13.9 vs. 13.2 h/d, respectively, SEM = 0.15 h/d), but both fan treatments prevented the reduction in LT observed in the control treatment as THI increased. Relative to the control, both fan treatments effectively reduced ST, RR, and VT and increased DMI and MY. In the control, average values were elevated for both RR (68.7 ± 1.5 breaths/min, mean ± SEM, greater than a common benchmark of 60 breaths/min) and VT (39.3 ± 0.05°C) but remained in the normal range in both fan treatments (54.2 vs. 50.7 breaths/min in the 60% vs. 100% fan power treatments; 39.0°C in both fan treatments). Both fan treatments resulted in greater overall MY (42.6 vs. 43.0 ± 0.4 kg/d in the 60% vs. 100% fan power treatments) relative to the control (41.0 kg/d) and similarly avoided the reduction in MY when -1 d THI increased. Compared with natural ventilation alone, fans delivering air speeds of at least 1 m/s at cow resting height were effective not only for reducing thermoregulatory responses, but also for maintaining lying time, DMI, and MY in heat stress conditions. This is the first study to demonstrate an intervention to improve animal welfare by maintaining lying times during periods of heat stress.

A review of thermal stress in cattle

Cattle control body temperature in a narrow range over varying climatic conditions. Endogenous body heat is generated by metabolism, digestion and activity. Radiation is the primary external source of heat transfer into the body of cattle. Cattle homeothermy uses behavioural and physiological controls to manage radiation, convection, conduction, and evaporative exchange of heat between the body and the environment, noting that evaporative mechanisms almost exclusively transfer body heat to the environment. Cattle control radiation by shade seeking (hot) and shelter (cold) and by huddling or standing further apart, noting there are intrinsic breed and age differences in radiative transfer potential. The temperature gradient between the skin and the external environment and wind speed (convection) determines heat transfer by these means. Cattle control these mechanisms by managing blood flow to the periphery (physiology), by shelter-seeking and standing/lying activity in the short term (behaviourally) and by modifying their coats and adjusting their metabolic rates in the longer term (acclimatisation). Evaporative heat loss in cattle is primarily from sweating, with some respiratory contribution, and is the primary mechanism for dissipating excess heat when environmental temperatures exceed skin temperature (~36°C). Cattle tend to be better adapted to cooler rather than hotter external conditions, with Bos indicus breeds more adapted to hotter conditions than Bos taurus. Management can minimise the risk of thermal stress by ensuring appropriate breeds of suitably acclimatised cattle, at appropriate stocking densities, fed appropriate diets (and water), and with access to suitable shelter and ventilation are better suited to their expected farm environment.

Temperature-humidity index monitoring during two summer seasons in dairy cow sheds in Mugello (Tuscany)

Many studies have reported that the impact of high temperatures affects physiology, welfare, health, and productivity of farm animals, and among these, the dairy cattle farming is one of the livestock sectors that suffers the greatest effects. The temperature-humidity index (THI) represents the state of the art in the evaluation of heat stress conditions in dairy cattle but often its measurement is not carried out in sheds. For this reason, the aim of this study was the monitoring of the THI in three dairy cattle farms in Mugello (Tuscany) to understand its influence on dairy cows. THI values were calculated using meteorological data from direct observation in sheds and outdoor environments. Data relating to the animal's behavior were collected using radio collars. The Pearson test and Mann-Kendall test were used for statistical analysis. The results highlighted a significant (P < 0.001) upward trend in THImax during the last 30 years both in Low Mugello (+ 1.1 every 10 years) and in High Mugello (+ 0.9 every 10 years). In Low Mugello sheds, during the period 2020-2022, more than 70% of daytime hours during the summer period were characterized by heat risk conditions (THI > 72) for livestock. On average the animals showed a significant (P < 0.001) decrease in time spent to feeding and rumination, both during the day and the night, with a significant (P < 0.001) increase in inactivity. This study fits into the growing demand for knowledge of the micro-climatic conditions within farms in order to support resilience actions for protecting both animal welfare and farm productivity from the effects of climate change. This could also be carried out thanks to estimation models which, based on the meteorological conditions forecast, could implement the thermal stress indicator (THI) directly from the high-resolution meteorological model, allowing to get a prediction of the farm's potential productivity loss based on the expected THI.

Effects of rumen-protective γ-aminobutyric acid additive on lactation performance and serum biochemistry in heat-stressed cows

In the context of global warming, heat stress has become one of the major stress factors limiting dairy cattle production. Although many methods have been explored to help cows mitigate the negative effects of heat stress during the hot summer months, maintaining the performance of high-yielding cows under heat stress is still a great challenge. The aim of this trial was to investigate the effect of RP-GABA in the diet on milk yield, milk composition and serum biochemical parameters in heat-stressed cows. Twenty Chinese Holstein cows in early lactation (51.00 ± 4.92 kg milk/d, 71 ± 10.94 d in milk and 2.68 ± 0.73 parities) were included in this experiment and randomly divided into four groups (n = 5/group). The four experimental groups consisted of one control group (0 g RP-GABA/d) and three treatment groups, given 5, 7.5 and 10 g RP-GABA/d of dry matter (DM) per cow, respectively. The results showed that supplementing high-yielding cows with 10 g/d of RP-GABA improved milk protein production but had no effect on the improvement of other production performance, the alleviation of heat stress in cows, or the improvement of immune function and antioxidant capacity. Ultimately, we conclude that the supplementation of 10 g/d RP-GABA to heat-stressed, high-yielding dairy cows can provide a degree of performance enhancement. Furthermore, our study provides some reference for nutritional improvement measures for summer heat stress in dairy cows, especially high-yielding cows.

Relationship between body temperature and behavior of nonpregnant early-lactation dairy cows

Animal behavior and management factors that influence behavior affect physiology and lactation performance. Circadian rhythms of core body temperature are a primary output of the master clock; however, core body temperature in early-lactation dairy cows showed poor fit to 24-h rhythms. We hypothesized that eating behavior was related to daily body temperature oscillations. The objectives of this study were to determine if oscillations in daily behaviors, specifically feeding behavior, were related to body temperature. The behavior of 11 Holstein cows (34 ± 14 d in milk; mean ± standard deviation) housed in a freestall barn was recorded every 10 min for a 48-h period. Simultaneously, data loggers (iButtons; iButtonLink Technology) recorded the body temperature of cows with the same sampling frequency. The mean temperature of all cows showed a better fit to a 2-component cosinor (R² = 0.54) than to a single cosinor model (R² = 0.26). Logistic regression showed that the probability (Pr) of a cow experiencing an increase in body temperature (increment, I) given that she was milking [Pr(I|milking) = 0.94] was higher than for ruminating [Pr(I|ruminating) = 0.69], lying [Pr(I|lying) = 0.66], feeding [Pr(I|feeding) = 0.16], standing [Pr(I|standing) = 0.54], and mounting [Pr(I|mounting) = 0.62]. The main limitations of this study are the length of the observation period and the sample size. Longer observation windows on core body temperature would allow to isolate the noise and the signal and identify patterns with more clarity. Oscillations in body temperature were not associated with feeding. However, findings indicate that milking, activity associated with walking to the parlor, or the temperature in the parlor may affect secondary rhythms of daily body temperature.

Heat ameliorative measures in Murrah buffalo (Bubalus bubalis) heifers during summer: effect on microclimate, thermal comfort, and behavior

Water buffalo (Bubalus bubalis) is the mainstay of milk production in Asian countries including India. However, the hot climate of the country remains the biggest bottleneck to exploit the potential of this species. Therefore, a study was conducted to assess the effect of heat ameliorative measures on microclimate, thermal comfort, and behavior of Murrah buffalo heifers during summer. Buffalo heifers (n = 24) between the age of 15 and 20 months with a mean body weight of 363.75 ± 11.27 kg were randomly grouped into four treatments based on their age and body weight. The heifers kept in the shed without any cooling served as CON (control), while the animals of group CJ were tied with a cooling jacket. The buffalo heifers of the CJF group were subjected to the cooling jacket with forced air ventilation, whereas the intermittent (10 min at 2-h intervals) sprinkling followed by forced air ventilation was practiced in group SF between 900 and 1800 h throughout the experiment. The microclimatic variables were low in the sheds of groups CJ, CJF, and SF than the CON. The physiological responses such as rectal temperature, skin temperature, respiration rate, and pulse rate were reduced in groups CJ, CJF, and SF than the CON at 1400 h. The serum cortisol was less in the CJF and SF than those of CON group. The animals of the CJ, CJF, and SF groups spent more time for feeding and rumination with less frequent longer bouts. The extended periods of lying followed by shorter standing and idling were observed in groups CJ, CJF, and SF when compared with the CON. It may be therefore concluded that cooling jacket and intermittent sprinkling in combination with forced air ventilation might be helpful in improving the micro-environment, thermal comfort, and behavior of buffalo heifers particularly under tropical climates during summer.

Heat Stress Effects on Physiological and Blood Parameters, and Behavior in Early Fattening Stage of Beef Steers

This study was conducted to investigate the effect of heat stress (HS) on physiological, blood, and behavioral parameters, according to the temperature-humidity index (THI), in beef steers. Twelve Korean native beef steers (342.7 ± 13.81 days old, body weight (BW) of 333.0 ± 18.53 kg) were used in this experiment. Beef steers were randomly distributed into three homogenized groups (four beef steers each) for 14 days, namely, threshold (THI = 64-71), mild-moderate (THI = 72-79), and severe (THI = 80-87). Feed and water intake were recorded daily. Physiological parameters, including heart rate and rectal temperature, and behavioral patterns (standing and lying down) were measured weekly. Blood was sampled every week to analyze hormones, heat shock protein (HSP) levels, metabolites, and hematological parameters. All data were analyzed using repeated-measures analysis. Beef steers exposed to severe THI had significantly increased (p < 0.001) water intake, heart rate, and rectal temperature compared to the threshold and mild-moderate THI beef steers. Additionally, increased blood cortisol (p < 0.001), HSP70 (p < 0.001), blood urea nitrogen (BUN) (p = 0.014), and time spent standing (p < 0.001) were observed in beef steers after exposure to severe THI compared to beef steers in the threshold and mild-moderate THI groups. However, dry matter intake, blood glucose, and non-esterified fatty acids were not different among the THI groups. In conclusion, heart rate, rectal temperature, blood cortisol, HSP70, BUN, and time spent standing were closely associated with severe HS conditions in beef steers. These phenomena indicated that beef steers exposed to HS modulated their behavior and blood parameters, as well as their physiological response, to maintain homeostasis.

A systematic review of the effects of silvopastoral system on thermal environment and dairy cows' behavioral and physiological responses

Does the silvopastoral system (SPS) promote a satisfactory thermal environment for dairy cows to perform their natural behaviors and perform a suitable thermoregulatory function? To answer this, peer-reviewed articles, written in English and evaluating the effects of silvopastoral systems on thermal environment, dairy cows' behavior, and physiology were used in this systematic review; additionally, a bibliometric approach was performed. Web of Science and Google Scholar were used to compile the literature. The resulting articles (1448) underwent a 4-step appraisal process and resulted in 19 articles that fitted our inclusion criteria. Microclimate variables and thermal comfort indicators were the most researched topics (discussed in 89% of studies); 47% of studies addressed cattle behavior and 36% physiological responses. Our review highlights different benefits of silvopastoral systems for grazing dairy cows. For example, the SPS provides a more comfortable thermal environment than treeless pasture, which increases feeding behaviors; furthermore, dairy cows in SPS show lower drinking events, surface temperature, and respiratory rate than cows raised in treeless pasture. However, for nine of the variables related to cows' behavior (e.g., resting, rumination) and physiology responses (e.g., internal temperature), the results of the studies were unclear. Furthermore, behaviors associated with lying down (e.g., idling and rumination) and milk production in SPS were explored only in six and two studies, respectively. These findings provide consistent evidence that the silvopastoral systems are beneficial to thermal comfort of dairy cows; nonetheless, the effect on cows' behavioral and physiological responses is still scarce and unclear.

Effects of tree arrangements of silvopasture system on behaviour and performance of cattle: a systematic review

This review aimed to provide a critical and systematic evaluation of the scientific literature about the effect of tree arrangements of the silvopasture system on the thermal environment, behaviour, and performance of cattle. We conducted a search using Web of Science and Google Scholar to identify the key literature of the theme. Peer-reviewed published articles written in English, comparing one or more tree arrangements of SPS to treeless pasture or comparing shaded and sunny areas within the SPS, were selected. The resulting manuscripts (n=191) underwent a four-step PRISMA appraisal process. This process resulted in a final sample of 37 articles, which were used for recording metadata, bibliometric analysis, and assessment of the results, using the software R. Of the 37 articles, 20 studies evaluated dairy cattle (behaviour: 14; performance: 7) and 17 evaluated beef cattle (behaviour: 6; performance: 12). The main behaviours evaluated were grazing (95%) and ruminating (90%), while weight gain (89%) was the main performance variable evaluated. The co-occurrence network analysis highlighted that the studies related the animals’ response to improving the thermal environment promoted by silvopasture systems. The main difference among tree arrangements evaluated by the studies was tree density, which ranged from 5 to 800 trees/ha; most studies covered SPS with row of trees (single row, n=16 and multiple rows, n=19). Most studies (n=32) were carried out in Brazil. The evidence of this review showed that regardless of tree arrangement, the silvopasture system improves the thermal environment for cattle, although some effects on behaviour and performance are inconclusive.

Effects of Different Bedding Materials on Production Performance, Lying Behavior and Welfare of Dairy Buffaloes

Different bedding materials have important effects on the behavioristics, production performance and welfare of buffalo. This study aimed to compare the effects of two bedding materials on lying behavior, production performance and animal welfare of dairy buffaloes. More than 40 multiparous lactating buffaloes were randomly divided into two groups, which were raised on fermented manure bedding (FMB) and chaff bedding (CB). The results showed that the application of FMB improved the lying behavior of buffaloes, the average daily lying time (ADLT) of buffaloes in FMB increased by 58 min compared to those in CB, with a significant difference (p < 0.05); the average daily standing time (ADST) decreased by 30 min, with a significant difference (p < 0.05); and the buffalo comfort index (BCI) increased, but the difference was not significant (p > 0.05). The average daily milk yield of buffaloes in FMB increased by 5.78% compared to buffaloes in CB. The application of FMB improved the hygiene of buffaloes. The locomotion score and hock lesion score were not significantly different between the two groups and all buffaloes did not show moderate and severe lameness. The price of FMB was calculated to be 46% of CB, which greatly reduced the cost of bedding material. In summary, FMB has significantly improved the lying behavior, production performance and welfare of buffaloes and significantly reduce the cost of bedding material.

Programming effects of late gestation heat stress in dairy cattle

The final weeks of gestation represent a critical period for dairy cows that can determine the success of the subsequent lactation. Many physiological changes take place and additional exogenous stressors can alter the success of the transition into lactation. Moreover, this phase is pivotal for the final stage of intrauterine development of the fetus, which can have negative long-lasting postnatal effects. Heat stress is widely recognised as a threat to dairy cattle welfare, health, and productivity. Specifically, late gestation heat stress impairs the dam's productivity by undermining mammary gland remodelling during the dry period and altering metabolic and immune responses in early lactation. Heat stress also affects placental development and function, with relevant consequences on fetal development and programming. In utero heat stressed newborns have reduced birth weight, growth, and compromised passive immune transfer. Moreover, the liver and mammary DNA of in utero heat stressed calves show a clear divergence in the pattern of methylation relative to that of in utero cooled calves. These alterations in gene regulation might result in depressed immune function, as well as altered thermoregulation, hepatic metabolism, and mammary development jeopardising their survival in the herd and productivity. Furthermore, late gestation heat stress appears to exert multigenerational effects, influencing milk yield and survival up to the third generation.

Heat abatement during the pre-weaning period: effects on lying behavior and disbudding-related responses of male Holstein calves

Strategies to abate heat stress are seldom adopted for pre-weaned dairy calves and little is known about their effects on behavior and pain sensitivity of youngstock. Our objectives were to determine the effects of heat stress abatement on lying behavior and disbudding-related pain sensitivity, wound healing, and change in intake. Male Holstein calves (n = 60; 0 to 68 d of age) were assigned randomly at birth (d 0) to 1 of 3 treatments: hutch outdoors with 50% of its area covered with plywood (control = 20), hutch in a barn with no cooling (SH = 21), and hutch in a barn with ceiling fans (SHF = 19). Calves were fitted with lying-behavior loggers on the hind leg from d 1 to 68. On d 32 ± 8 (±SD), we disbudded calves using hot iron, 30 min after cornual nerves were blocked with lidocaine. Immediately before (0 h), and at 1, 2, and 3 h after disbudding, we evaluated calves for mechanical nociceptive threshold (MNT) and head (ear flick, head shake, head rubbing) and somatic (tail flicking, foot stamping, restlessness) behaviors. On d 1, 3, 7, and 14 after disbudding, we evaluated the MNT and, on d 7 and 14, we evaluated wound healing (1 = crust, 5 = exudate). We calculated the relative change in milk solids and starter intake from d 0 to 6 relative to disbudding compared with the average of the 72 h preceding the procedure. The lying time was 0.6 h/d greater for the SHF treatment compared with the SH treatment. The control treatment resulted in 3.2 and 4.1 more lying bouts per day than the SH and SHF treatments, respectively; consequently, the control treatment resulted in lying-bout duration 7.7 and 10.9 min/event shorter than the SH and SHF treatments, respectively. We did not detect an effect of treatment on the number of disbudding-related head and somatic behaviors and MNT. The odds of calves having abnormal wound was 3.5 and 3.2 times greater for the control treatment compared with the SH and SHF treatments, respectively. We did not detect an effect of treatment on the relative change in intake of milk solids and starter. Heat abatement improves the welfare of pre-weaned dairy calves and may hasten healing.

Milking time behavior of dairy cows in a free-flow automated milking system

The objective of this preliminary observational study was to determine milking time behavior of cows in a free-flow automated (robotic) milking system (AMS) and identify potential factors that influenced the time waiting to be milked. Milking time behavior of 40 cows from 1 pen on a commercial dairy farm with a free-flow AMS was evaluated using video analysis over 2 d. For each study cow, data were assessed for waiting time to access the milking robot, the use of the fetch pen, robot refusals, and their lying behavior. On average, cows visited the robot to wait to be milked 6 times per day, for 15 min per visit, for a total daily waiting time of 88 min per cow (range 5 to 322 min). Daily waiting time was longer for primiparous cows and decreased with increasing days in milk, but this effect interacted with parity. Daily waiting time and number of visits to the robot were associated with voluntary use of the fetch pen. Furthermore, cows with long daily waiting times had shorter daily lying times compared with cows with short daily waiting times (9.5 vs. 11.1 h/d). It is possible that factors related to the design and layout of the AMS entry and fetch pen had an effect on waiting behavior. We inferred that adoption of grouping strategies intended to reduce competitive behavior, especially toward primiparous cows, could improve milking time behavior in a free-flow AMS. This preliminary observational data from a single herd highlights the need to confirm the findings across multiple AMS herds, both with free-flow and guided-flow systems.

Predictive Models of Dairy Cow Thermal State: A Review from a Technological Perspective

Simple Summary

Heat stress in cattle is broadly defined as a physiological condition in which body temperature rises, and the animals are no longer able to adequately dissipate body heat to maintain thermal equilibrium due to environmental factors. Dairy cattle are particularly sensitive to heat stress because of the higher metabolic rate needed for milk production. Due to global warming and the expected growth of milk production in warmer regions, an increase in the occurrence of heat stress can only be avoided with the use of environmental control systems. However, most available systems were developed to take corrective measures or are not accurate enough to effectively prevent heat stress, as there is not yet an automated technological solution that considers all the environmental and animal variables that determine the occurrence of this condition. Further, these systems must be connected in time to prevent this condition in cattle but also disconnected when they are no longer needed, as their use raises major economic and environmental concerns regarding energy and water consumption. This review describes and discusses three types of predictive models that can make these systems more effective in preventing heat stress and more efficient in the use of energy and water.

Abstract

Dairy cattle are particularly sensitive to heat stress due to the higher metabolic rate needed for milk production. In recent decades, global warming and the increase in dairy production in warmer countries have stimulated the development of a wide range of environmental control systems for dairy farms. Despite their proven effectiveness, the associated energy and water consumption can compromise the viability of dairy farms in many regions, due to the cost and scarcity of these resources. To make these systems more efficient, they should be activated in time to prevent thermal stress and switched off when that risk no longer exists, which must consider environmental variables as well as the variables of the animals themselves. Nowadays, there is a wide range of sensors and equipment that support farm routine procedures, and it is possible to measure several variables that, with the aid of algorithms based on predictive models, would allow anticipating animals’ thermal states. This review summarizes three types of approaches as predictive models: bioclimatic indexes, machine learning, and mechanistic models. It also focuses on the application of the current knowledge as algorithms to be used in the management of diverse types of environmental control systems.

Heat stress in a temperate climate leads to adapted sensor-based behavioral patterns of dairy cows

Most research on heat stress has focused on (sub)tropical climates. The effects of higher ambient temperatures on the daily behavior of dairy cows in a maritime and temperate climate are less studied. With this retrospective observational study, we address that gap by associating the daily time budgets of dairy cows in the Netherlands with daily temperature and temperature-humidity index (THI) variables. During a period of 4 years, cows on 8 commercial dairy farms in the Netherlands were equipped with neck and leg sensors to collect data from 4,345 cow lactations regarding their daily time budget. The time spent eating, ruminating, lying, standing, and walking was recorded. Individual cow data were divided into 3 data sets: (1) lactating cows from 5 farms with a conventional milking system (CMS) and pasture access, (2) lactating cows from 3 farms with an automatic milking system (AMS) without pasture access, and (3) dry cows from all 8 farms. Hourly environment temperature and relative humidity data from the nearest weather station of the Dutch National Weather Service was used for THI calculation for each farm. Based on heat stress thresholds from previous studies, daily mean temperatures were grouped into 7 categories: 0 = (<0°C), 1 = (0-12°C, reference category), 2 = (12-16°C), 3 = (16-20°C), 4 = (20-24°C), 5 = (24-28°C), and 6 = (≥28°C). Temperature-humidity index values were grouped as follows: 0 = (THI <30), 1 = (THI 30-56, reference category), 2 = (THI 56-60), 3 = (THI 60-64), 4 = (THI 64-68), 5 = (THI 68-72) and 6 = (THI ≥72). To associate daily mean temperature and THI with sensor-based behavioral parameters of dry cows and of lactating cows from AMS and CMS farms, we used generalized linear mixed models. In addition, associations between sensor data and other climate variables, such as daily maximum and minimum temperature, and THI were analyzed. On the warmest days, eating time decreased in the CMS group by 92 min/d, in the AMS group by 87 min/d, and in the dry group by 75 min/d compared with the reference category. Lying time decreased in the CMS group by 36 min/d, in the AMS group by 56 min/d, and in the dry group by 33 min/d. Adaptation to daily temperature and THI was already noticeable from a mean temperature of 12°C or a mean THI of 56 or above, when dairy cows started spending less time lying and eating and spent more time standing. Further, rumination time decreased, although only in dry cows and cows on AMS farms. With higher values for daily mean THI and temperature, walking time decreased as well. These patterns were very similar for temperature and THI variables. These results show that dairy cows in temperate climates begin to adapt their behavior at a relatively low mean environmental temperature or THI. In the temperate maritime climate of the Netherlands, our results indicate that daily mean temperature suffices to study the effects of behavioral adaptation to heat stress in dairy cows.

Effects of Exposure to Heat Stress During Late Gestation on the Daily Time Budget of Nulliparous Holstein Heifers

Exposure of dairy cows to heat stress negatively affects welfare and performance during all phases of the lactation cycle. Detrimental effects include decreased milk and reproductive performance, reduced immune status and health, and altered natural behaviors. While we understand how mature cows respond to heat stress, the effects of late gestation heat stress on pregnant heifers is still unknown. Automated monitoring devices were used to document the behavioral activity of heifers during the pre- (final 60 d of gestation) and postpartum (first 60 d of lactation) periods. Twenty-five pregnant Holstein heifers were housed in a free-stall barn and enrolled to heat stress (HT; shade; n = 13) or cooling (CL; shade, soakers and fans; n = 12) treatments during the last 60 days of gestation. All animals were provided active cooling postpartum. Upon enrollment, heifers were fitted with a leg tag, which measured daily lying time, number of steps, and standing bouts, and a neck tag that measured eating and rumination times. Rectal temperatures (RT) and respiration rates (RR) were measured thrice weekly during the prepartum period. Relative to CL, HT heifers had elevated RT (38.8 vs. 38.7 ± 0.04°C) and RR (59.6 vs. 44.4 ± 1.9 breaths/min) during the prepartum period. Heat-stressed heifers tended to spend more time eating (224 vs. 183 min/d) and less time ruminating (465 vs. 518 min/d) during the prepartum period compared to CL, but dry matter intake did not differ. During the postpartum period, HT heifers spent more time eating (209 vs. 180 min/d) during weeks 1–4 of lactation, but rumination time was similar. Lying time was reduced by 59 and 88 min per day during weeks −7 and −6 prepartum and 84 and 50 min per day during weeks 2 and 3 postpartum in HT heifers, relative to CL. The number of steps was greater for HT during the postpartum period, from weeks 2 to 9 (3019 vs. 2681 steps/d). Eating frequency was similar during pre- and postpartum periods, however, based on semi quantitative visualization of the smarttag reports, HT consumed larger meals at night during the pre- and postpartum periods compared with CL heifers. In summary, late-gestation exposure to heat stress affects the daily time budget of first lactation heifers during both the pre- and postpartum periods. Current insights of heat stress effects on behavioral responses of dairy heifers may contribute to the development of more effective management strategies to mitigate heat load.

Environmental variables responsible for Zebu cattle thermal comfort acquisition

The aim of this study was to estimate, using data mining, which microclimate and behavioral variables affect the behavior of animals to seek shaded or sunny areas. The experiment was carried out between January and May 2016 in an integrated crop-livestock-forest system. In this system, we defined two different areas: shaded and sunny. Microclimatic variables (At, BGt, RH, and WS) were measured in each area on 4 consecutive days per month. With these variables, we determined the bioclimatic indicators (THI, BGHI, HLI, MRT, RTL, and ETI). In addition, we calculated the absolute difference (Δ) by subtracting the value recorded in shaded areas from the value recorded in sunny areas for all microclimatic variables and bioclimatic indicators, except for WS. The behaviors (grazing, ruminating, and other activities), posture (standing or lying), and use of areas (shaded or sunny) of 38 Zebu cattle were recorded on 2 consecutive days per month. The data mining technique was applied for analysis in a classification task. The model correctly classified 76% of the instances with a Kappa statistic of 0.51 after features selection from the database. The ΔBGt was the most important feature in the model to classify the decision of Zebu cattle to seek another area or remain in a determined area. The model was built with seven classification rules, being one simple rule, composed of the interaction between ΔBGt and rumination; and other more complex rules, composed of the interactions among the ΔBGt, WS, and rumination. The preference of Zebu cattle to seek or remain in shaded or sunny areas was influenced by eight features: rumination, drinking water, WS, ΔBGt, MRT in shade, BGHI in sun, ΔBGHI, and HLI in sun.

Developing of a model to predict lying behavior of dairy cows on silvopastoral system during the winter season

Lying behavior is an important indicator of the cows' welfare and health. In this study, we evaluate the effect of the physical environment on dairy cows' behaviors raised on a silvopastoral system through a predictive model. There was a difference (p<0.01) in soil surface temperature (SST) and black globe-humidity index (BGHI) between the shaded and sunny areas of the silvopastoral system. The BGHI was the variable most important to classify the cows' decision to seek shaded or sunny areas, while the soil surface temperature affected the choice for the area to perform the lying behaviors. In order to understand the influence of these parameters on cows' lying behavior, we developed another predictive model relating the SST and BGHI with cows lying at shaded and sunny areas. There was significance (p<0.01) for all model parameters. The odds of cows lying increased by approximately 2% with each degree of SST. In contrast, the probability of the cows lying in the shaded areas was 35% less than in sunny areas. The model developed in this study was efficient in identifying changes in the behavior of dairy cows in relation to physical environment. The BGHI influenced the areas used by cows to performing their standing behavior, while the areas used for lying behavior were influenced by the SST.

Responses of beef calves to long-term heat stress exposure by evaluating growth performance, physiological, blood and behavioral parameters

The objective of this study was to explore the responses of beef calves to long-term heat stress (HS) exposure at various levels in comparison with the animals under thermoneutral conditions by evaluating growth performance, physiological, blood, and behavioural parameters. Data were collected from sixteen beef calves (BW: 136.9 ± 6.23 kg; age: 169.6 ± 4.60 d) kept at four stress levels of designated temperature humidity index (THI): threshold (22-24 °C, 60%; THI = 70 to 73), mild (26-28 °C, 60%; THI = 74 to 76), moderate (29-31 °C, 80%; THI = 81 to 83), and severe (32-34 °C, 80%; THI = 89 to 91) stress levels in climatic controlled chambers. Feed and water intake were recorded daily, and body weight was measured once a week. Blood was sampled every three days to analyse metabolite parameters. Dry matter intake (DMI) (p = 0.069, tendency) and blood glucose levels (p = 0.028) were decreased after sudden exposure to HS conditions (severe THI levels). Also, blood cortisol (p = 0.002), glutamic-oxaloacetic transaminase (GOT) (p = 0.009), blood urea nitrogen (BUN) (p = 0.004) and standing time (p = 0.009) were increased in moderate and severe THI levels compared with threshold after exposure to HS conditions. However, in the severe THI group, blood cortisol (p < 0.05), glucose (p < 0.05), GOT (p < 0.05) and BUN (p < 0.05) levels were returned to normal range after 6-13 days of continuous HS exposure. In conclusion, DMI, blood cortisol, GOT, glucose, BUN, and standing time were closely associated with long-term HS condition in beef calves. In addition, calves exposed to HS modulated their physiological responses that resulted in the regulation of the pertinent blood metabolites in the blood to maintain homeostasis during the long-term HS.

The effects of cow-related factors on rectal temperature, respiration rate, and temperature-humidity index thresholds for lactating cows exposed to heat stress

The objectives of this study were to investigate the effects of the cow-related factors on rectal temperature (RT) and respiration rate (RR) of lactating dairy cows under different heat stress (HS) conditions and establish the temperature-humidity index (THI) thresholds at which RT and RR begin to increase for cows in China. Cow-related factors included body posture (standing and lying), milk yield (<26 kg/d, ≥ 26-39 kg/d, and ≥39 kg/d), days in milk (≤60 d, > 60 and ≤ 150 d, and >150 d), and parity (1, 2, and ≥3). Records of RT, RR, and individual characteristics were collected from July to October 2020 on a commercial dairy farm in Northern China, where 826 Holstein lactating cows were measured. Using the broken-stick regression models and the entire dataset, the THI thresholds for RT and RR were 69.8 and 67.1, respectively. Therefore, the heat stress conditions during this study were classified according to the THI levels as thermoneutrality (TN, 60 < THI ≤ 67), mild (67 < THI ≤ 72), moderate (72 < THI ≤ 80), and severe (80 < THI ≤ 86). Results showed that lying cows exhibited the higher RT and RR but the lower THI threshold for RT (68.8 vs. 70.7) and RR (65.6 vs. 68.4) than standing cows; milk yield is positively associated with the values of RT and RR under TN or HS conditions, and the THI thresholds for RT (70.2 vs. 70.0 vs. 68.0) and RR (68.1 vs. 64.7 vs. 64.7) were progressively lower for low-yielding, middle-yielding, and high-yielding cows; there was a significant increase in RT and RR in early-lactation cows compared to late-lactation cows under TN or HS conditions (P < 0.001), and the lowest THI threshold (67.8 for RT and 64.7 for RR) was observed in early-lactation cows, followed by mid-lactation cows (68.2 for RT and 65.3 for RR) and late-lactation cows (70.0 for RT and 67.3 for RR); the effects of parity were not significant on RT (P > 0.05), but significant on RR (P < 0.001). The THI thresholds for RT (69.2) and RR (66.0) were lowest for cows in 3rd-parity and higher, followed by cows in 2nd-parity (70.0 for RT and 68.9 for RR) and 1st-parity (70.7 for RT and 66.6 for RR). This study highlighted the great significance of considering the cow-related factors in heat stress responses and THI threshold assessment. For dairy cows in China, we suggest that cooling should be initiated when THI reaches 65 to 66.

Lying Behaviour in Dairy Goats: Effects of a New Automated Feeding System Assessed by Accelerometer Technology

Simple Summary

Goat farming is becoming more important in Germany and as dehorning is forbidden, it is necessary to facilitate animal welfare among horned and mixed-horned herds. In this study an optimized automatic concentrated feeding system was installed in a mixed-horned herd and lying behaviour was detected by accelerometer technology. Results show a seasonal progression of lying behaviour in dairy goats and an adjustment of behavioural differences between horned and hornless goats with the new feeding system.

Abstract

The aim of this study was to evaluate lying behaviour in dairy goats before and after installation of an optimized automatic concentrated feeding system (AFS). A mixed-horned herd of Bunte Deutsche Edelziege was used. As many agonistic interactions between goats happen at the feeding place, a new automated feeding system was installed to better fulfil the needs of horned goats. Lying behaviour is an indicator to ascertain animal welfare of ruminants. In order to measure lying behaviour accelerometer technology was used and verified by video analyses. The results show an agreement of 99.62–99.93% per lying time by comparing accelerometers to video data. Over all goats, a mean ± SD lying time (LT) of 11.78 ± 1.47 h/d, a mean ± SD lying bout duration (LBD) of 0.51 ± 0.10 h/bout and a mean ± SD frequency of lying bouts (FLB) of 24.35 ± 5.57 were found. Lying behaviour follows a seasonal progression with significant lowest LBD and highest FLB in summer. With the old AFS significant differences in LBD and FLB were detected between horned and hornless goats, but with the new AFS results were adjusted. Findings suggest that changes in feeding management do not affect the general seasonal progression of lying behaviour but can affect the behavioural differences between horned and hornless dairy goats.

Sensor and Video: Two Complementary Approaches for Evaluation of Dairy Cow Behavior after Calving Sensor Attachment

Studies evaluating calving sensors provided evidence that attaching the sensor to the tail may lead to changes in the cows' behavior. Two different calving sensors were attached to 18 cows, all of which were equipped with a rumen bolus to record their activity. Two methodological approaches were applied to detect potential behavioral changes: analysis of homogeneity of variance in cow activity (5 days pre-sensor and 24 h post-sensor) and analysis of video-recorded behavior (12 h pre- and post-sensor, respectively) in a subgroup. The average results across the sample showed no significant changes in the variability of activity and no statistically significant mean differences in most visually analyzed behaviors, namely walking, eating, drinking, social interaction, tail raising, rubbing the tail, and the number of standing and lying bouts after calving sensor attachment. In addition to considering mean values across all cows, individual cow investigations revealed an increased number of time slots showing a significant increase in the variability of activity and an increased frequency of tail raising and rubbing the tail on objects after calving sensor attachment in some cows, which should be investigated in more detail on a larger scale.

Environmental impacts of implementing basket fans for heat abatement in dairy farms

Health and welfare impairments in dairy cows have been described to increase environmental impacts of milk production due to their negative effect on cow productivity. One of the welfare problems is heat stress, which is gaining importance even in temperate regions. While improving animal welfare may reduce emissions, the mitigation potential depends on the environmental costs associated with specific intervention measures. Taking abatement of heat stress as an example, the aim of the present study was to estimate the effect of implementing mechanical ventilation devices on the contribution potential of milk production to global warming (GWP), terrestrial acidification (TAP) and freshwater eutrophication (FEP). Environmental impacts of two modelled production systems located in alpine and lowland production areas of Austria were estimated before and after the implementation of basket fans, using life cycle assessment. Region-specific climate data were retrieved to determine the number of days with heat stress and to evaluate heat stress-induced productivity shortfalls in the baseline scenario (S_basic). In the intervention scenario with increased ventilation (S_vent), this decline was assumed to be eliminated due to the convective cooling effect of fans. For S_basic, mean GWP, TAP and FEP impacts were estimated at 1.2 ± 0.09 kg CO₂-, 21.1 ± 1.44 g SO₂- and 0.1 ± 0.04 g P-equivalents per kg milk, respectively. Independent from the production system, in S_vent, implementation of fans did not result in significant environmental impact changes, except for FEP of the alpine system (+5.9%). The latter reflects the comparatively high environmental costs of additional cooling regarding FEP (+2.3%) in contrast to GWP (+0.4%) and TAP (+0.1%). In conclusion, the estimated overall effects of mechanical ventilation on GWP, TAP and FEP of milk production were minor and the model calculations point to the potential of heat stress abatement to at least outweigh the environmental costs associated with fan production and operation. To confirm this trend, further assessments are needed, which should be based on primary data regarding the effectiveness of fan cooling to improve cow productivity, and on emission calculation schemes that are sensitive to environmental factors such as wind speed and temperature.

Evaluation of thermal indices based on their relationships with some physiological responses of housed lactating cows under heat stress

Thermal indices as environmental risk indicators have been used to assess heat stress of dairy cows. The present study aimed to evaluate the predictive performance of the typical cattle-related thermal indices by comparing their prediction to heat stress levels and associations with some physiological responses. The study was conducted from August to September 2019 in a naturally ventilated barn in Jiangsu, China. Nine typical cattle-related thermal indices, i.e., temperature-humidity index (THI), black globe temperature index (BGHI), equivalent temperature index, effective temperature (ET) for dairy cows, respiratory rate predictor (RRP), adjusted temperature-humidity index (THIadj), heat load index (HLI), comprehensive climate index (CCI), and equivalent temperature index for cattle (ETIC), were evaluated. Respiration rate (RR) and body surface temperature (BST) were collected twice per day from a total of 287 lactating cows, 18 of which were continuously measured vaginal temperature (VT). Over the experimental period, the average daily RR, VT, and BST were 55.8 breaths/min, 38.7 °C, and 32.3 to 36.4 °C that depend on body positions, respectively. The study found that the prediction of THI, BGHI, THIadj, and CCI was closer to the actual heat stress conditions which were mild to moderate heat stress. Correlation analyses showed that RR, VT, and BST correlated most closely with effective temperature (r = 0.580; P < 0.05), BGHI (r = 0.642; P < 0.05), and CCI (r = 0.849; P < 0.05). In this evaluation, based on the comprehensive performance of CCI in the relatively accurate prediction to heat stress level and duration, detection on environmental differences between standing and lying zone, and correlations with some physiological responses, CCI is seemingly the promising thermal index to assess heat stress of housed dairy cows.

Invited review: Lying time and the welfare of dairy cows

Adequate time lying down is often considered an important aspect of dairy cow welfare. We examine what is known about cows' motivation to lie down and the consequences for health and other indicators of biological function when this behavior is thwarted. We review the environmental and animal-based factors that affect lying time in the context of animal welfare. Our objective is to review the research into the time that dairy cows spend lying down and to critically examine the evidence for the link with animal welfare. Cows can be highly motivated to lie down. They show rebound lying behavior after periods of forced standing and will sacrifice other activities, such as feeding, to lie down for an adequate amount of time. They will work, by pushing levers or weighted gates, to lie down and show possible indicators of frustration when lying behavior is thwarted. Some evidence suggests that risk of lameness is increased in environments that provide unfavorable conditions for cows to lie down and where cows are forced to stand. Lameness itself can result in longer lying times, whereas mastitis reduces it. Cow-based factors such as reproductive status, age, and milk production influence lying time, but the welfare implications of these differences are unknown. Lower lying times are reported in pasture-based systems, dry lots, and bedded packs (9 h/d) compared with tiestalls and freestalls (10 to 12 h/d) in cross-farm research. Unfavorable conditions, including too few lying stalls for the number of cows, hard or wet lying surfaces, inadequate bedding, stalls that are too small or poorly designed, heat, and rain all reduce lying time. Time constraints, such as feeding or milking, can influence lying time. However, more information is needed about the implications of mediating factors such as the effect of the standing surface (concrete, pasture, or other surfaces) and cow behavior while standing (e.g., being restrained, walking, grazing) to understand the effect of low lying times on animal welfare. Many factors contribute to the difficulty of finding a valid threshold for daily lying time to use in the assessment of animal welfare. Although higher lying times often correspond with cow comfort, and lower lying times are seen in unfavorable conditions, exceptions occur, namely when cows lie down for longer because of disease or when they spend more time standing because of estrus or parturition, or to engage in other behaviors. In conclusion, lying behavior is important to dairy cattle, but caution and a full understanding of the context and the character of the animals in question is needed before drawing firm conclusions about animal welfare from measures of lying time.

Microclimate modeling in naturally ventilated dairy barns during the hot season: Checking the accuracy of forecasts

Monitoring and predicting the microclimate in naturally ventilated barns (NVB) is important given the adverse effects of high summer temperatures on dairy cows in the context of global climate change. The aim of the work was to verify the accuracy of the microclimate forecast in a NVB using linear regression (LR). Our working hypothesis suggested that multiple periodic measurements of air temperature and relative humidity outside and inside the barns at the same time will allow us to build LR models for predicting the temperature-humidity index (THI). This was done not only for a specific dairy barn based on this indicator outside, but also in other dairy barns with a similar design, located in similar weather conditions. The results of the research indicate that the use of LR had a high accuracy of forecasting (93-96%) the THI in NVB of various designs during the summer heat. At the same time, differences were found between traits (air temperature, relative humidity as well as resulting THI) provided by meteorological weather stations and these data measured simultaneously next to the dairy barns. The proposed LR models can be used to predict THI in NVBs of different designs.

Graduate Student Literature Review: Heat abatement strategies used to reduce negative effects of heat stress in dairy cows

The southeastern United States experiences an extended hot season with a high environmental temperature and relative humidity. With increasing global temperatures, managing dairy cattle in regions with tropical, subtropical, and Mediterranean climates is becoming an increasing challenge. Heat-stressed cows will decrease feed intake, decrease productivity, and increase respiration rate in an attempt to maintain internal body temperature. Temperature-humidity index (THI) is a unitless value that has been used to measure the magnitude of heat stress on dairy cows. Many researchers have studied the THI threshold at which dairy cattle begin to experience heat stress. When housing cows in a confinement setting, a pasture-based setting, or a combination of the two, the appropriate heat abatement should be implemented to allow cows to perform to their potential and to improve overall animal welfare. This review summarizes heat abatement strategies that have been studied to reduce the negative effects of heat stress.

Behavioral changes associated with fever in transition dairy cows

Dairy cows are often diagnosed with fever without showing clinical symptoms of disease. The aim of this study was to investigate changes in feeding, social, and lying behaviors of cows with fever but without clinical disease, as compared with healthy cows. After parturition, dairy cows of mixed parities were housed in a dynamic group of 20. In the freestall pen, cows had access to 12 electronic feed bins, 2 electronic water bins, and 24 lying stalls. Feeding and social behaviors were recorded using the electronic feed bins, and lying behaviors were measured using electronic data loggers attached to the cow. Rectal body temperature was assessed on a daily basis, and fever defined as a body temperature >39.5°C. All cows were examined for metritis every third day after calving, and all other diseases (e.g., mastitis, ketosis) were diagnosed as per farm protocol. Cows with multiple days of fever (n = 8) and cows with 1 d of fever (n = 18) that were not diagnosed with a clinical disease were compared with a matched sample of healthy cows (i.e., cows that were not clinically ill and never had a fever recorded) of the same parity (categorized as primiparous vs. multiparous). Feeding, social, and lying behaviors were compared for the first 2 d of fever in cows with multiple days of fever, and the day of fever in cows with 1 d of fever. Cows of both fever groups spent less time feeding compared with controls (135 vs. 181 ± 7.6 min/d for multiple fever days, and 158 vs. 185 ± 9.7 min/d for 1 d of fever). Cows with 1 d of fever ate at a faster rate (109 vs. 91 ± 5 g/min) and had a lower number of replacements at the feed bunk (actor replacements: 9.7 vs. 14.6 ± 1.7 no./d; reactor replacements: 11.1 vs. 15.9 ± 1.6 no./d) compared with healthy controls. Overall, cows with fever showed behavioral changes such as decreased feeding time that are consistent with sickness responses described in other species.

Impact of heat stress on lactational performance of dairy cows

Lactating dairy cows exhibit a myriad of responses to heat stress. These responses partially facilitate the thermal balance between heat gain and heat loss, but also account for reduction in productivity. Decreased milk yield is the most recognized impact of heat stress on a dairy cow and results in significant economic loss to dairy producers. The reduced milk yield by heat stress is observed when daily average temperature-humidity index exceeds 68, above which the milk yield of a cow is negatively correlated with temperature-humidity index or dry bulb temperature. Milk yield is also positively correlated with body temperature of the cows under evaporative cooling, which reflects the positive relationship between metabolic heat production and milk yield. During summer, feed intake is positively correlated with milk yield, and the decreased intake explains at least half of the reduction in milk yield by heat stress. These emphasize the importance of maintaining intake on productivity during summer. Although not entirely clear, mechanisms that mediate the reduced milk yield by heat stress in addition to intake may be multifactorial. These could include but are not limited to altered metabolism, potential activation of immune system and inflammation, changes in behavior, and altered mammary gland development and function.

Effects of rumen-protected methionine on lactation performance and physiological variables during a heat stress challenge in lactating Holstein cows

Milk yield, content, and composition are altered by heat stress. Thirty-two multiparous, lactating Holstein cows [balanced by days in milk (mean ± standard deviation; 184 ± 59); body surface area (5.84 ± 0.34 m²)] were randomly assigned to 1 of 2 dietary treatments [total mixed ration with rumen-protected Met (RPM; Smartamine M; Adisseo Inc., Antony, France; 1.05 g of RPM/kg of dry matter intake) or total mixed ration without RPM (CON)], and within each dietary treatment group cows were randomly assigned to 1 of 2 environmental treatment groups in a split-plot crossover design. The study was divided into 2 periods with 2 phases per period. In phase 1 (9 d), all cows were in thermoneutral conditions and fed ad libitum. In phase 2 (9 d), group 1 (n = 16) was exposed to a heat stress challenge (HSC) using electric heat blankets. Group 2 (n = 16) remained in thermoneutral conditions but was pair-fed (PFTN) to HSC counterparts. After a 21-d washout period, the study was repeated (period 2) and the environmental treatments were inverted relative to treatments from phase 2 of period 1, whereas dietary treatments (RPM or CON) remained the same for each cow. Cows were milked 3× per day and samples were taken on d 1, 5, and 9 of each phase. Vaginal temperature was measured every 10 min, rectal temperature and skin temperature were measured 3× per day, and respiration rate and heart rate were recorded once per day. Cow activity was measured using an accelerometer. Paired difference values were calculated for each cow for each period based on the difference between phase 1 baseline means and phase 2 values for each variable. Cows in HSC had a greater increase in vaginal temperature and respiration rate (+0.2°C and +13.7 breaths/min, respectively) compared with cows in PFTN (0.0°C and -1.6 breaths/min, respectively). Cows in PFTN had a greater decrease in dry matter intake and milk yield (-3.9 and -2.6 kg/d, respectively) compared with cows in HSC (-3.2 and -0.9 kg/d, respectively). Cows in CON had a greater decrease in milk protein concentration for PFTN (-0.10 percentage units) and HSC (-0.06 percentage units) compared with cows in RPM for PFTN (0.00 percentage units) and HSC (-0.02 percentage units). Cows in CON for HSC had greater decrease in milk fat concentration compared with cows in RPM for HSC (-0.10 and +0.12 percentage units, respectively). In conclusion, HSC altered physiological and production parameters of cows. Additionally, RPM helped maintain milk protein and fat concentration during HSC, whereas dry matter intake, milk yield, and feed efficiencies were not affected by RPM.

Symposium review: The impact of management and facilities on cow culling rates

This symposium review examines the association between comfort and cow longevity, with a particular emphasis on optimizing resting behavior in confinement-housed systems. Housed dairy cattle demonstrate a variety of negative behavioral and physiological effects when lying time is restricted, with cows prioritizing the recovery of rest over feeding when both are deprived. There is, however, wide individual-cow variation in daily lying times, influenced by an array of cow-, housing-, and management-related factors. Cow-related factors include individual preference, parity, stage of lactation cycle, milk yield, ill health, and lameness. Lying time tends to increase with age and days in milk and during periods of ill health, whereas milk yield is negatively correlated with lying time. The effect of lameness is complicated by severity and by interactions with bedding type, which modifies the cows' ability to rise and lie down. Generally, lame cows suffer prolonged lying bouts of greater variability in length and take fewer bouts per day. Often this results in an overall increase in lying time. Thus, higher standards of cow comfort and improved cow health are not always reflected by longer lying times. Housing and management factors that influence resting behavior include the design of the resting area, access to the resting space, and the thermal microenvironment of the lying area. Provision of dry, deep loose bedding, stocking cows to allow each animal access to a resting space, allowing sufficient time to access the resting area, and providing heat abatement to reduce heat load optimize resting behavior. Because lameness and poor body condition are commonly found in culled dairy cattle, the link between cow comfort and culling is likely mediated through lameness onset and management. Optimal comfort helps prevent the onset of lameness and facilitates recovery once cows become lame, which limits the effect of lameness on feeding behavior and reduces the risk for other health-related disorders, poor reproductive performance, and early herd removal. Cow comfort cannot be assessed by measuring the duration of lying time alone. Rather, comfort is reflected by the optimization of resting behavior, providing facilities and management to allow cows to lie down when they choose to do so for as long as they need to.