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Simple Summary: A better understanding of cattle behavioural responses during high environmental temperatures could be beneficial for the diagnosis of heat loads. In the current study, 24 Black Angus steers fed a finisher diet based on cereal grain or a substituted diet (8% of the grain replaced by an isoenergetic amount of lucerne hay) were exposed to hot conditions, and changes in their behavioural and physiological dynamics were assessed. Compared to the recovery period, hot conditions increased respiration rate and were associated with increased stepping behaviour, especially by left limbs. Cattle also increased the orientation of their heads downward, their ears backward, and their tail vertically or raised, and they reduced eating, grooming, and scratching during the heat load period. Changes in head, ear and tail position, breathing changes persisted during the heat load period, suggesting that these behaviours have diagnostic value. Cattle that were fed a diet based on the cereal grain stood for longer and were more likely to hold their ears backward and tail vertically, whereas those on the substituted diet were more likely to display axial ears and hold their head in a neutral position. We conclude that cattle have subtle changes in behaviour in response to hot conditions, which may be of value for diagnostic purposes. 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 DMI steer-1 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. [ABSTRACT FROM AUTHOR]

Vietnamese smallholder dairy cows (VDC) are the result of crossbreeding between different zebu (ZEB) and taurine dairy breeds through many undefined generations. Thus, the predominant breed composition of VDC is currently unknown. This study aimed to evaluate the level of genetic diversity and breed composition of VDC. The SNP data of 344 animals from 32 farms located across four dairy regions of Vietnam were collected and merged with genomic reference data, which included three ZEB breeds: Red Sindhi, Sahiwal and Brahman, three taurine breeds: Holstein (HOL), Jersey (JER) and Brown Swiss (BSW), and a composite breed: Chinese Yellow cattle. Diversity and admixture analyses were applied to the merged data set. The VDC were not excessively inbred, as indicated by very low inbreeding coefficients (Wright's FIS ranged from −0.017 to 0.003). The genetic fractions in the test herds suggested that the VDC are primarily composed of HOL (85.0%); however, JER (6.0%), BSW 5.3%) and ZEB (4.5%) had also contributed. Furthermore, major genotype groupings in the test herds were pure HOL (48%), B3:15/16HOL_1/16ZEB (22%) and B2:7/8HOL_1/8ZEB (12%). The genetic makeup of the VDC is mainly components of various dairy breeds but also has a small percentage of ZEB; thus, the VDC could be a good genetic base for selecting high milk‐producing cows with some degree of adaptation to tropical conditions. [ABSTRACT FROM AUTHOR]

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 , °C) was collected every 10 min, and respiration rate ( RR , breaths per minute), panting score ( PS ), and water usage (L·steer -1 ·day -1 ) were obtained at multiple time points daily, by trained observers. Individual animal daily DMI was also determined. Morning (0700 hours) rectal temperature ( RecT , °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., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)

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.