Early diagnosis of heat load in beef cattle remains a challenge due to the limited understanding of behaviour-based indicators. This preliminary longitudinal study aimed to validate behavioural and physiological responses previously identified as heat load indicators. Black Angus steers were exposed to high environmental temperatures expected to cause heat load in the following sequence: an initial thermoneutral period, a hot period, and a recovery period. Changes in the positioning of key body parts, feeding behaviour, body maintenance, respiratory dynamics, and eye temperature were monitored. In the hot period, cattle increased their respiration rate, panting, and infrared eye temperature. Increased stepping by their left limbs suggested involvement of the right brain hemisphere in a stress response to high environmental temperatures. Cattle also held their heads more downward, ears backward, and their tail vertical, and reduced eating, grooming, and scratching during the hot period. Cattle responses to hot conditions were persistent in the recovery period, reflecting diagnostic relevance of the head, ear, and tail movements, stepping, especially by left limbs, and infrared eye temperature as non-invasive tools to identify heat load condition in cattle. The study reinforces our understanding of the specific behavioural and physiological responses to heat load condition, especially those involving left-limb stepping, ear and tail posture, and infrared eye temperature, are reliable indicators for identifying cattle experiencing high environmental temperature.

The extent of, and limits of, the metabolic flexibility of feedlot cattle to cope with heat loads of varying intensity and duration is a research gap. Two cohorts of 12 Black Angus steers were housed in climate-controlled rooms (CCR) and subjected to three thermal periods: PreChallenge (5 days), Challenge (7 days) and Recovery (5 days). PreChallenge and Recovery provided thermoneutral conditions. The Challenge simulated a strong heatwave. Finally, the steers were returned to outdoor pens for 20 days. The animals were bled on days 3, 5, 7, 8, 9, 10, 11, 12, 13, 15, 17, 24 and 38. A clinical plasma biochemistry panel was used to measure the concentrations of major metabolites and electrolytes. During Challenge, energy metabolites fell (except for β-hydroxybutyrate). Creatinine, urea and total bilirubin rose rapidly. In Recovery, the major liver enzymes were released into plasma, and total bilirubin remained high. Most analytes showed non-linear relationships with core temperatures during Challenge, suggesting threshold-dependent responses rather than gradual dose-dependent adjustments. The responses and relationships differed from those reported for moderate heat load challenge and recovery. We integrated the metabolic changes over the course of the experiment with previously reported metabolic hormone and physiological responses of these steers.

Globally, feedlots rely on weather data to provide foundational information describing and predicting cattle exposure to heat load throughout the summer months. Anecdotally, in Australia feedlots are installing weather stations in close proximity to office buildings, for ease of maintenance. However, there is limited information available describing the variability of microclimatic conditions within feedlots, nor do recommendations exist regarding the ideal placement of weather stations to provide an accurate representation of the thermal environment experienced by feedlot cattle. The aim of this study was to evaluate the variability between in pen microclimate obtained from within pen data loggers, and weather stations situated at feedlot pens and in close proximity to the feedlot office. A total of six (n = 6) Australian feedlots covering a broad geographical range were enrolled into this study. Each feedlot had an automated weather station located in close proximity to i) office buildings (50-75 m from office) and second station located at ii) feedlot pens (2-10 m from pens). In addition (n = 16) ambient temperature (TA, °C) and relative humidity (RH, %) data loggers were placed within a number of pens at each feedlot. From these data comparisons between within pen, at pen and office climatic conditions were evaluated. The relationships between the climatic variables on the two weather stations located at each feedlot were determined using regression analysis, where linear and quadratic relationships were evaluated. Results from this study provides evidence highlighting the variability of within feedlot microclimate conditions, emphasising the importance of onsite weather monitoring. Weather station placement at feedlots is important to ensure that the data collected provides an accurate representation of the feedlot climate conditions. This study highlights the importance of identifying the ideal location for correct weather stations placement for feedlots. Failing to position onsite weather stations in an appropriate location may result in an under- or over-estimation of heat load that cattle are experiencing, which likely reduces the effectiveness of heat load mitigation strategies utilised.

This study evaluated the effects of including additional roughage and the timing of roughage addition on rumen temperature (TRUM), rumen pH, dry matter intake as a percentage of live weight (DMILW), water consumption as a percentage of live weight (WILW) and average daily gain of grain-fed steers exposed to a simulated heat wave. A total of forty-eight Black Angus steers (539.53 ± 4.95 kg) were housed within climate control rooms for 21 days and exposed to a 5-day simulated heat wave. Steers were randomly allocated into four cohorts with 12 steers/cohort, and then allocated to one of three dietary treatments: Treatment 1 (T1) were fed a finisher diet for the 21 days; Treatment 2 (T2) transitioned from the finisher diet to a heat load diet on d 9 and fed the heat load diet until d 14; and Treatment 3 (T3) transitioned from the finisher diet to the heat load diet on d 7 and fed the heat load diet until d 14. On d 15, T2 and T3 transitioned back to the finisher diet. The study was categorised into five phases consisting of (i) Phase I, d 0–6 (Temperature Humidity Index, THI 65 to 78); (ii) Phase II, d 7–8 (THI 65 to 78); (iii) Phase III, d 9–11 (THI 83 to 90); (iv) Phase IV, d 12–13 (THI 78 to 85); and (v) Phase V, d 14–20 (THI 65 to 78). During the heat wave challenge in Phase III, all Treatments exhibited lower DMILW (p < 0.0001), greater TRUM and rumen pH (p < 0.0001), lower ranges in TRUM and rumen pH (p ≤ 0.0005) and altered diurnal TRUM and rumen pH rhythms. Average daily gain was not influenced by Treatments (p ≥ 0.98). Overall, these results suggest that nutritional management remains an important consideration to reduce the impact of hot climatic conditions on the rumen environment during heat wave and post-heat wave conditions.

The extent of endocrine changes in response to various levels of heat stress and subsequent recovery is not well understood. Two cohorts of 12 Black Angus steers were housed in climate-controlled rooms (CCR) and subjected to three thermal periods: PreChallenge (5 d), Challenge (7 d) and Recovery (5 d). PreChallenge and Recovery provided thermoneutral conditions. The Challenge simulated a strong heatwave. Finally, the steers were maintained in outdoor pens for 38 d. Rumen temperature (RumT), respiration rate (RR) and panting score (PS) were intensively measured in the CCR. Dry matter intake (DMI) was determined daily. The steers were bled most days, and a rectal temperature (RecT) was taken also. Plasma concentrations of TSH, prolactin, T3, T4, insulin, leptin and adiponectin were determined. During the Challenge, RumT, RecT, RR and PS rose; DMI was reduced. Plasma T3, T4 and adiponectin levels fell also. In Recovery, RumT, RecT, RR and PS fell below the PreChallenge mean. DMI partially recovered. T4 and adiponectin levels remained suppressed alongside lowered insulin. There were linear relationships between T3 concentration and THI, and T3 and T4 levels and DMI only. We highlight comparisons with previously reported metabolic hormone responses of grain-fed Black Angus steers to a moderate-heat-load challenge.

This study investigated nutritional management strategies to reduce the impact of heat stress on feedlot steers. Twelve Angus steers (582 ± 8.92 kg LW) were housed in climate control rooms (CCR) for 21-days. Steers were randomly allocated to three treatments: 1) Control, fed a finisher diet (Control); 2) finisher diet to a heat load diet with 5 % additional roughage, from d4 until d16 (HL Ration); 3) finisher diet supplemented with calcareous marine algae (CMA; 70 g/steer/day Acid Buf, Celtic Sea Minerals), between d4 until d16. The 21-days consisted of three phases i) d0 to d6, Phase I, Temperature Humidity Index, THI 65 to 78; ii) d7 to d11 Phase II, THI 83 to 87); and iii) d12 to d20, Phase III, THI 65 to 78, for all steers. Cattle exhibited increased respiration rate (RR), panting score (PS) and rumen temperature (TRUM) during Phase II (P < 0.0001). During Phase II, dry matter intake (DMI) was approximately 5 kg lower when compared with Phase I. The diurnal rhythm in rumen pH and range in rumen pH differed during Phase II for both Control (P < 0.0001) and CMA (P < 0.0001), when compared with Phase I. Mean rumen pH was lower during Phase III compared with Phase I (P ≤ 0.002). During Phase II, Lipopolysaccharide binding protein (LBP) and Serum amyloid A (SAA) differed across the treatments, with CMA cattle exhibiting the lowest concentrations (P ≤ 0.04). Both Aspartate aminotransferase (AST) (P ≤ 0.009) and Glutamate dehydrogenase (GLDH) (P ≤ 0.004) were at a maximum during Phase III, with Control having greater AST (P ≤ 0.01) and GLDH (P ≤ 0.04). These results suggest that CMA supports DMI and markers of gut integrity, whilst potentially mediating liver damage, during heat wave events.

Cattle are increasingly exposed to hot temperatures as a result of climate change, and a better understanding of behavioural responses could be beneficial for the diagnosis of heat loads. The changes in the positioning of key body parts, feeding behaviour, body maintenance, and respiratory dynamics were assessed in 24 Black Angus steers individually exposed to hot conditions and fed a finisher diet based on cereal grain or a substituted diet (8% of the grain replaced by an isoenergetic amount of lucerne hay). Increased respiration rate during the heat load period, compared to the recovery period, was associated with increased stepping, especially by left limbs. Cattle also reduced eating, grooming, and scratching during the heat load period. The lowered head, backward ear, vertical or raised tail, and increased respiration rate and panting persisted in cattle during the heat load period. Cattle on the cereal grain diet stood for longer and were more likely to hold their ears backward and tail vertical than those on the substituted diet. We conclude that these behaviours could be used to detect animals that are most affected and that changing from a cereal-based diet to a substituted diet containing a higher amount of fibre, such as lucerne hay, can reduce hyperthermic behavioural responses to a heat load.

Cattle in regions with high ambient temperatures are at risk of heat stress. Early detection is important to allow action to be taken to minimise the risks to cattle exposed to thermal stress. This study aimed to investigate the impact of heat stress on IRT-Eye temperature and its association with the behavioural and physiological responses of heat-stressed Angus steers (n = 24) on finisher and or substituted diets. Overall, 2 cohorts of 12 Angus steers were individually housed in a climate-controlled facility to examine responses to heat stress when fed on a standard finisher diet, based on a high percentage of cereal grains, and on a substituted diet in which 8% of the grains were replaced by an isoenergetic amount of lucerne hay. Exposing feedlot cattle to hot environmental conditions increased IRT-Eye temperature, which had a strong association with behaviour and physiology. There was no evidence of differences between the different dietary cohorts. The cattle with increased IRT-Eye temperature showed stress-related responses, including a downward-facing head, ears directed backwards, and other indicators of heat stress such as increased panting, standing, and increased rumen temperature. The strong association of IRT-Eye temperature with stress-related behaviours, as well as with rumen temperature and panting behaviour, highlights the potential for IRT-Eye to be utilised as a non-invasive tool to assess cattle responses in hot conditions.

Abstract During summer, feedlot cattle are often subjected to multiple high heat load events which can cause heat stress and negatively impact on cattle performance and well-being. The objective of this study was to evaluate the effects of different dietary buffering feeding strategies, on dry matter intake (DMI), water intake (WI), rumen temperature (TRUM), rumen pH and average daily gain (ADG) of grain-fed beef steers exposed to a simulated heat wave event. Angus steers [n = 12; body weight (BW) = 582 ± 8.92 kg] were housed within climate control rooms for 21 d and randomly allocated into one of three dietary treatments (4 steers/treatment): 1) Treatment 1 (T1), finisher diet; 2) Treatment 2 (T2), transitioned from finisher to heat load diet (HLD) on d 4 and fed HLD until d 16; 3) Treatment 3 (T3), fed finisher and supplemented with a calcareous marine algae (CMA; Acid Buffer, Celtic Sea Minerals) on d 4 until d 16. On d 17, T2 and T3 transitioned back to the finisher. Days were split into three phases consisting of i) d 0 to 6 [PI, Temperature Humidity Index (THI), THI 65-78]; ii) d 7 to 11 (PII, THI 83-87); iii) d 12 to 20 (PIII, THI 65-78). Data were analyzed using a repeated measures model, with a first order auto-regressive error structure, including fixed effects for treatment, phase, day and hour, with animal ID as a random effect. Body weight declined (P < 0.005) during PII, with steers losing on average, 17.65 ± 3.06 kg BW/steer (T1), 12.30 ± 3.06 kg BW/steer (T2) and 16.20 ± 3.06 kg BW/steer (T3) at conclusion of PII, with muscle atrophy visually evident (Table 1). There were no effects (P ≥ 0.93) for treatment on ADG. During PII, DMI decreased (P < 0.005), with T2 and T3 having >2kg DMIּ steer-1ּ d-1 greater (P ≤ 0.006) DMI compared with T1. During PIII, T1 maintained decreased (P ≤ 0.001) DMI compared with T2 and T3. During PII, mean WI increased (P ≤ 0.05) for T1 and T3, although remained unchanged (P = 0.11) for T2, TRUM increased (P < 0.0001), whilst range in TRUM decreased (P ≤ 0.01) for all TRT and rumen pH for T2 and T3 decreased (P ≤ 0.0003), whilst T1 tended (P ≥ 0.05) to decrease. Rumen pH diurnal rhythms were disrupted during PII, range in rumen pH also reduced (P < 0.0001) for T1 and T3, remaining unchanged (P = 0.94) for T2. Mean rumen pH was lower (P ≤ 0.002) during PIII compared with PI for all treatments. Both T2 and T3 had a lower (P ≤ 0.05) range in rumen pH than T1 during PIII. Data from the current study suggest that feeding strategies to include CMA may aide in moderating DMI reductions observed during and post-heat stress periods, whilst also reducing the range in rumen pH during post-heat wave conditions when rumen dysfunction challenges may present.

Feedlot cattle are at times exposed to high environmental temperatures. Faecal cortisol metabolites (FCM), were related to possible indicators of heat stress that could be measured under field conditions: respiratory dynamics (respiration rate; RR), body surface temperature and adaptive behaviours, such as water consumption, posture (standing, lying), and activity (eating, drinking and rumination). Twelve (12) yearling Black Angus steers were divided into two treatment groups: a hot treatment (HOT; n = 6) and a thermoneutral-treatment (TN; n = 6) and individually housed in a climate-controlled facility at The University of Queensland, Australia. In the TN treatment all animals were exposed to an ambient temperature of 20.34 ± 0.25°C, relative humidity 71.51 ± 3.26% and Temperature humidity index (THI) 66.91 ± 0.33 throughout. In the HOT treatment group environmental conditions were exposed to different climatic phases from thermoneutral to hot conditions, where they remained for 7 d, and then returned to TN conditions in the recovery period. The dry bulb ambient temperature (TA) and relative humidity (RH) in the pens of cattle in the HOT treatment was increased from 28°C (daily maximum ambient temperature) and 45% RH at 0700 h to a daily maximum TA and RH of 35°C (daily maximum ambient temperature) and 50% (THI 77) at 1100 h, which was maintained until 1600 h, after which it declined until it reached the baseline at 2000 h. In both treatments, there was a significant decrease in faecal cortisol metabolites concentration from the start to the end of the experiments they adapted to the experimental facility. The concentration of faecal cortisol metabolites was greater in the HOT treatment, compared to the TN treatment during the heat exposure period, but there was no difference in the transition or recovery periods. Respiration rate was greater in the HOT treatment during heat exposure, and it increased with ambient dry bulb temperature above 26°C, the latter being the upper critical temperature. Although positive correlations were detected between faecal cortisol metabolites and body surface temperature measurements, particularly the shoulder and rump, as well as standing time, panting score and drinking, a stepwise regression found that faecal cortisol metabolites was only significantly correlated with one variable, respiration rate. It is concluded that respiration rate is the best indicator of the stress induced by hot conditions for cattle.

Abstract Insult to the gastrointestinal tract (GIT) during heat stress has profound effects on epithelium integrity and subsequent regulation of inflammatory immune responses. The objective of this study was to evaluate the effects of different dietary buffering feeding strategies, on serum amyloid A (SAA), lipopolysaccharide-binding protein (LBP), aspartate aminotransferase (AST), glutamate dehydrogenase (GLDH), gamma-glutamyl transpeptidase (GGT), alkaline phosphatase (ALP), partial pressure of carbon dioxide (pCO2), base excess (BE), blood pH and bicarbonate (HCO3) of grain-fed steers exposed to a simulated heat wave event. Angus steers [n = 12; body weight (BW) = 582 ± 8.92 kg) were housed within climate control rooms for 21 d and randomly allocated into one of three dietary treatments (4 steers/treatment): 1) Treatment 1 (T1), finisher diet; 2) Treatment 2 (T2), transitioned from finisher to heat load diet (HLD) on d 4, fed HLD until d 16; 3) Treatment 3 (T3), fed finisher and supplemented with a calcareous marine algae (CMA; Acid Buffer, Celtic Sea Minerals) on d 4 until d 16. On d 17, T2 and T3 transitioned back to finisher. Days were split into three phases consisting of i) d 0 to 6 [PI, Temperature Humidity Index (THI), 65-78); ii) d 7 to 11 (PII, THI 83-87); iii) d 12 to 20 (PIII, THI 65-78). Individual steer jugular vein blood samples (40 mL) were obtained on d 0, 4 (PI), 7 to 11 (PII), 12 to 17, 18 and 20 (PIII), with plasma extracted. Data were analyzed using a repeated measures model, with a first order auto-regressive error structure, including fixed effects for treatment, phase and day, animal ID as a random effect. During PII, all steers had decreased pCO2 (P < 0.0001), HCO3 (P < 0.04) and BE (P < 0.01), indicating compensated respiratory alkalosis associated with hyperventilation, as blood pH remained unchanged (P = 0.15; Table 1). Both AST (P ≤ 0.009) and GLDH (P ≤ 0.004) were at a maximum during PIII, with T1 having greater AST (P ≤ 0.01) and GLDH (P ≤ 0.04) compared with T2 and T3. Greater AST and GLDH are suggestive of liver damage with reduced detoxifying capabilities becoming overloaded during PII. Interestingly, GGT remained similar (P ≤ 0.94) for TRT × phase, it remains unclear why, warranting further exploration. Alkaline phosphatase was decreased (P < 0.0001) for all treatments during PII and PIII compared with PI, potentially ALP was diverted to the GIT to aide in protection from endotoxemia. During PII, SAA tended to increase (P = 0.08), LBP remained at similar (P = 0.12) levels to PI, before both inflammatory markers decreased (P ≤ 0.05) during PIII. Observationally, steers had gut lining epithelium (mucin casts) within their feces from d 10 to 13. In conclusion, the heat wave initiated a respiratory alkalosis, upregulation of inflammatory marker SAA and mucin casts within feces, suggestive of acute heat stress. Subsequent liver damage, as indicated by greater AST and GLDH post-heat wave, were potentially mediated by inclusion of CMA in the diet.

Heat wave intensity, frequency, and duration are increasing in many regions of the world, including locations where highly productive livestock are raised. There are animal health and welfare, as well as economic impacts from these events. In this study, the physiological responses of grain-fed steers during a high heat load challenge through to recovery in climate-controlled rooms (CCR) were intensively evaluated. Two cohorts of 12 Black Angus steers (BW, 615.4 +/- 40.1 kg) sequentially underwent a simulated heatwave event that consisted of 3 phases in the CCR: PreChallenge (5 d duration and temperature humidity index (THI) range of 65 to 71), Challenge (7-d duration and THI 66 to 95 with diurnal cycling), and Recovery (5 d duration and THI 65 to 70). The Challenge period was modeled on a severe heat wave, characterized by 3 very hot days. Individual rumen temperature (RumT, degrees C) was collected every 10 min, and respiration rate (RR, breaths per minute), panting score (PS), and water usage (Lsteer-1day-1) were obtained at multiple time points daily, by trained observers. Individual animal daily DMI was also determined. Morning (0700 hours) rectal temperature (RecT, degrees C) was measured on days 3, 5, 7 to 13, 15, and 17. Not unexpectedly, RumT, RecT, RR, and PS rose during Challenge and fell rapidly as conditions eased. Conversely, DMI was reduced during Challenge. During the transition between PreChallenge and Challenge, there were abrupt increases in RumT, and RR. It was also very apparent that during Recovery the steers did not return to the baseline PreChallenge state. Compared to PreChallenge, Recovery was characterized by persistent lowered daily mean RumT (P = 0.0010), RecT (P = 0.0922), RR (P = 0.0257), PS (P <= 0.0001), and DMI (P <= 0.0001). These results provide evidence that these steers have undergone an allostatic response in response to high heat load, and the new adjusted physiological state post-heat event may not be transient. Imposition of a high heat load challenge mimicking a 7-d severe heat wave event on grain-fed feedlot steers resulted in abrupt changes in DMI, rumen temperature, and respiration rate. The cattle did not return to the PreChallenge state after 5 d of recovery. During Recovery, steers exhibited an overadjustment resulting in low rumen temperature, respiration rate, and DMI suggesting that these animals underwent an allostatic response. Extreme weather events such as severe heat waves are more frequently affecting cattle production globally. This study aimed to understand the differences in the physiological responses of cattle undergoing exposure to a high heat load challenge, as compared to a moderate heat load. A previous study highlighted that during moderate heat load, grain-fed cattle easily adjusted core body temperature, respiration rate (RR), panting score (PS), and dry matter intake (DMI) but were able to reverse these changes during recovery to return to the PreChallenge (pre-heatwave) state. This reversal did not happen under the high heat load scenario presented here. Changes to body temperature, RR, PS, and DMI were abrupt, and there was rapid readjustment after the heat wave had peaked. In Recovery, the cattle overcorrected the PreChallenge state to become persistently hypothermic, with low RR and PS, while DMI only partially recovered. This suggests that the cattle underwent an allostatic response that resulted in a new state of reduced appetence, metabolism, and growth post-exposure to the high heat load event. These results indicate that the expectations of the future performance of cattle that have experienced severe heat waves need to be adjusted accordingly.

Exposure to weather extremes, such as heatwaves, can cause discomfort, harm, or death in grazing cattle in pastures. While the Australian Bureau of Meteorology issues sheep graziers alerts when there is an exposure risk to chill for livestock, there is no equivalent alert for heat stress for Australian cattle. Before any such alert system can be developed, a robust assessment and comparison of relevant cattle thermal stress indices is required. This study evaluates and compares the multiyear climatology of three cattle thermal heat stress indices across Australia in the warm season months (October - March). The same indices are then used to assess historical Australian heat events where cattle died from heat exposure. These events are based off official records and survey responses from northern Australian graziers. In the seven historical heat events studied, high relative humidity combined with low wind speeds, or high solar exposure combined with high surface temperatures, exacerbated the impact of heat stress on cattle. In the two historic events where multiple compounding weather factors combined (e.g., high humidity, low winds, and high solar exposure), the cattle mortality levels were significantly high. These events were characterized by rainy conditions followed by a rapid warming, meaning cattle were likely unable to acclimatize to such dramatic temperature changes. This study highlights the need for using more than one thermal stress index when verifying cattle heat stress events and, importantly, calls for further research on standardizing the risk classifications of these thermal indices for cattle in Australia ' s variable climate.

Genomic selection (GS) and genome-wide association studies (GWAS) have not been investigated in Vietnamese dairy cattle, even for basic milk production traits, largely due to the scarcity of individual phenotype recording in smallholder dairy farms (SDFs). This study aimed to estimate heritability (h 2) and test the applicability of GS and GWAS for milk production, body conformation and novel heat tolerance traits using single test day phenotypic data. Thirty-two SDFs located in either the north (a lowland vs. a highland) or the south (a lowland vs. a highland) of Vietnam were each visited for an afternoon and the next morning to collect phenotype data of all lactating cows (n = 345). Tail hair from each cow was sampled for subsequent genotyping with a 50K SNP chip at that same visit. Milk production traits (single-test day) were milk yield (MILK, kg/cow/day), energy corrected milk yield adjusted for body weight (ECMbw, kg/100 kg BW/day), fat (mFA, %), protein (mPR, %) and dry matter (mDM, %). Conformation traits were body weight (BW, kg) and body condition score (BCS, 1 = thin to 5 = obese). Heat tolerance traits were panting score (PS, 0 = normal to 4.5 = extremely heat-stressed) and infrared temperatures (IRTs, °C) at 11 areas on the external body surface of the cow (inner vulval lip, outer vulval surface, inner tail base surface, ocular area, muzzle, armpit area, paralumbar fossa area, fore udder, rear udder, forehoof and hind hoof), assessed by an Infrared Camera. Univariate linear mixed models and a 10-fold cross-validation approach were applied for GS. Univariate single SNP mixed linear models were applied for the GWAS. Estimated h 2 (using the genotype information to build relationships among animals) were moderate (0.20-0.37) for ECMbw, mFA, mPR, mRE, BW, BCS and IRT at rear udder; low (0.08-0.19) for PS and other IRTs; and very low (≤ 0.07) for MILK, ECM and mDM. Accuracy of genomic estimated breeding values (GEBVs) was low (≤ 0.12) for MILK, ECM, mDM and IRT at hind hoof; and moderate to high (0.32-0.46) for all other traits. The most significant regions on chromosomes (BTA) associated with milk production traits were 0.47-1.18 Mb on BTA14. Moderate to high h 2 and moderate accuracies of GEBVs for mFA, mPR, ECMbw, BCS, BW, PS and IRTs at rear udder and outer vulval surface suggested that GS using single test day phenotypic data could be applied for these traits. However, a greater sample size is required to decrease the bias of GEBVs by GS and increase the power of detecting significant quantitative trait loci (QTLs) by GWAS.

Context Transport of cattle can be stressful and may lead to increased body temperature. It is necessary to quantify the effect of transport on body temperature so that informed management decisions can be made. Aims This study aimed to determine the effects of a 5.5 h, 430 km road transport journey on body temperature (TB) of feedlot steers. Methods Body temperature was obtained at 30 min intervals. All cattle were weighed and randomly allocated to a truck pen prior to transport. Cattle were transported on a single B-double truck, with three upper-deck and three lower-deck compartments. At 0630 hours, cattle were walked from their pens (25 m), weighed and loaded onto the truck. Loading was completed by 1030 hours. Key results During the weighing and loading process prior to transport, mean TB increased from 39.37 ± 0.11°C to 40.21 ± 0.11°C. Immediately following loading, mean TB increased. The TB of cattle on the upper deck was 40.96 ± 0.08°C and on the lower deck 40.89 ± 0.08°C (P = 0.6299). During the first 3 h of the journey, the TB of lower-deck cattle decreased by 1.14°C (P < 0.01), compared with a 0.83°C reduction in cattle on the upper deck. Over the duration of the journey, which took 1 h longer than expected, the mean TB of the cattle on the upper deck (40.47 ± 0.11°C) was greater (P < 0.0001) than that on the lower deck (40.04 ± 0.12°C). One hour after unloading at the abattoir, pooled TB was 40.26 ± 0.12°C. Minimum TB (38.87 ± 0.04°C) occurred at 10.5 h after unloading. Conclusions The results from this study highlight that increases in TB were more associated with cattle handling and loading events, rather than transport, under these environmental conditions. Understanding the magnitude of this increase will help managers decide on pre- and post- transport management of cattle. Implications Cattle handling and loading for transport may lead to an increase in TB, which can remain elevated for a number of hours. However, it is unclear what the impact of hotter climatic conditions would have on trailer microclimate and, as such, TB regulation during road transport.

Cattle change their behaviour in response to hot temperatures, including by engaging in stepping that indicates agitation. The automated recording of these responses would be helpful in the timely diagnosis of animals experiencing heat loading. Behavioural responses of beef cattle to hot environmental conditions were studied to investigate whether it was possible to assess behavioural responses by video-digitised image analysis. Open-source automated behavioural quantification software was used to record pixel changes in 13 beef cattle videorecorded in a climate-controlled chamber during exposure to a simulated typical heat event in Queensland, Australia. Increased digitised movement was observed during the heat event, which was related to stepping and grooming/scratching activities in standing animals. The 13 cattle were exposed in two cohorts, in which the first group of cattle (n = 6) was fed a standard finisher diet based on a high percentage of cereal grains, and the second group of cattle (n = 7) received a substituted diet in which 8% of the grains were replaced by lucerne hay. The second group displayed a smaller increase in digitised movements on exposure to heat than the first, suggesting less discomfort under hot conditions. The results suggest that cattle exposed to heat display increased movement that can be detected automatically by video digitisation software, and that replacing some cereal grain with forage in the diet of feedlot cattle may reduce the measured activity responses to the heat.

Healthy adult horses can balance accumulation and dissipation of body heat to maintain their body temperature between 37.5 and 38.5 °C, when they are in their thermoneutral zone (5 to 25 °C). However, under some circumstances, such as following strenuous exercise under hot, or hot and humid conditions, the accumulation of body heat exceeds dissipation and horses can suffer from heat stress. Prolonged or severe heat stress can lead to anhidrosis, heat stroke, or brain damage in the horse. To ameliorate the negative effects of high heat load in the body, early detection of heat stress and immediate human intervention is required to reduce the horse’s elevated body temperature in a timely manner. Body temperature measurement and deviations from the normal range are used to detect heat stress. Rectal temperature is the most commonly used method to monitor body temperature in horses, but other body temperature monitoring technologies, percutaneous thermal sensing microchips or infrared thermometry, are currently being studied for routine monitoring of the body temperature of horses as a more practical alternative. When heat stress is detected, horses can be cooled down by cool water application, air movement over the horse (e.g., fans), or a combination of these. The early detection of heat stress and the use of the most effective cooling methods is important to improve the welfare of heat stressed horses.

The aim of this study was to assess effects on milk yield (MY), rumen temperature, and panting score when lactating dairy cows were cooled during the day only or during the day and night. The study was conducted over 106 d during using 120 multiparous Holstein-Friesian cows assigned to 2 treatments (60 cows/treatment; 2 pens/treatment): (1) day cooling (DC): overhead sprinklers (large droplet) and fans while in the dairy holding yard only, shade and fans at the feedpad, and a shaded loafing area; and (2) enhanced day+night cooling (EDN): overhead sprinklers (large droplet) and fans in dairy holding yard, ducted air blowing onto cows during milking, plus thorough wetting (shower array) on exit from dairy; shade and fans at feedpad (turned off at night); and shaded loafing area + ducted fan-forced air blowing onto cows at night. The ducted air at night was manually activated at 2030 h when the maximum daily temperature-humidity index exceeded 75 and remained on until 0430 h the next day. The cows were fed a total mixed ration ad libitum, and feed intake was determined on a pen basis. Rumen temperature and cow activity were obtained from each cow at 10-min intervals via rumen boluses. Panting scores were obtained by direct observation 4 times a day at approximately 0430, 0930, 1530, and 2030 h. Cows were milked twice daily: 0500 to 0600 h and 1600 to 1700 h. Individual MY were obtained at each milking and combined to give individual daily totals. The EDN cows had greater daily MY (+2.05 kg/cow per day) over the duration of the study compared with DC cows. Rumen temperature during the third heat wave was lower for EDN (39.51 ± 0.01°C) than for DC (39.66 ± 0.01°C) cows. During the most severe heat wave (heat wave 3), MY for the 2 groups was similar, but over the 6 d following the heat wave, EDN cows had greater daily MY (+3.61 kg/cow per day). Rumen temperature was lower for EDN (39.58 ± 0.01°C) than for DC (40.10 ± 0.01°C) cows.