Physiological responses of Bos taurus and Bos indicus cattle to prolonged, continuous heat and humidity1

Abstract

Two experiments were conducted to investigate the physiological responses of Bos taurus (Angus cross, n = 6) and Bos indicus (Brahman, n = 6) cattle to prolonged heat and humidity, as can occur during live export by sea. Each experiment was carried out in climate-controlled rooms, where heifers were exposed to 15 d of sustained heat and humidity. The treatment was designed to be representative of a long-haul, live-export voyage leaving a southern Australian winter and traveling to a Middle Eastern summer. Wet bulb temperature (WBT) was used to give a combined measure of dry bulb temperature and relative humidity and was increased over several days, culminating in 5 d at 32 degrees C WBT between d 7 and 11. By d 11, the respiratory rate and core body temperature increased (P < 0.001) compared with values at lower ambient temperature on d 1 and 2 when climate-controlled rooms were not operating. Feed intake of Bos taurus was reduced (P < 0.001) by d 11, whereas that of Bos indicus did not change (P = 0.14). Despite no diurnal variation in climatic conditions, core body temperature of both Bos taurus and Bos indicus continued to show a circadian amplitude of approximately 1 degrees C throughout the hottest period. This amplitude increased during the recovery period after heat was removed (up to 1.8 degrees C for Bos indicus and 1.6 degrees C for Bos taurus). Water intake for both Bos taurus and Bos indicus increased when WBT increased (P < 0.01 on d 11). Significant acid-base and blood electrolyte imbalances occurred in both Bos taurus and Bos indicus, with changes in Bos taurus being more substantial and prolonged. The increase in respiratory rate coincided with a decrease in the partial pressures of carbon dioxide and bicarbonate in venous blood. However, during the hottest period, average daily venous blood pH remained unchanged. When the heat load was reduced after d 11, the blood pH decreased, indicating metabolic acidosis. Blood pH declined from 7.44 to 7.36 for Bos taurus (P < 0.001) and from 7.44 to 7.38 for Bos indicus (P < 0.001). Other parameters measured include heart rate; packed cell volume; plasma and urine Na, K, and Cl; urine pH; and specific gravity. Our results suggest that Bos taurus cattle experience significant physiological changes during exposure to prolonged and continuous high heat and humidity, with alterations persisting for some days after the heat-stress conditions subside. Bos indicus experience similar but less pronounced physiological changes.

A Survey of the Relationship between Climatic Heat Stress Indices and Fundamental Milk Components Considering Uncertainty

“…Protein seems to be less sensitive than fat to the negative effects of heat stress and climate variability. The results in this study agree with the results reported by other studies, such as [47][48][49][50][51][52][53].…”

Comportamento ingestivo de novilhas de corte em pastagem de gramíneas anuais de estação quente

“…Dentre os efeitos do estresse calórico estão o menor consumo de matéria seca e maior ingestão de água em novilhas Bos taurus quando comparadas com novilhas Bos indicus (Beatty et al; Tabela 5 -Equações de regressão múltipla das variáveis de comportamento ingestivo de novilhas de corte em pastagens de milheto e papuã A concentração da atividade de pastejo das novilhas aconteceu na ocasião na qual as temperaturas eram mais amenas, no amanhecer e no entardecer (Figura 1) quando mais de 50% dos animais encontravam-se em atividade de pastejo.…”

Effect of whole cottonseed v. sunflower seed on the fatty acid profile of subcutaneous fat, longissimus dorsi and blood of Thai Native and Holstein bulls

“…The latter observation is corroborated by the outcome of a study from Marchello et al (1967), who found a decrease in iodine number and an increase in melting point of subcutaneous fat of sheep that experienced higher ambient temperatures. Therefore, the difference in susceptibility to heat stress between the two breeds (Beatty et al, 2006;Wang et al, 2014), can be a factor to explain the difference in FA profile of their body fat. It can speculated that the Holstein bulls in this region with average maximum daily ambient temperatures above 30°C experienced more heat stress than their Thai Native counterparts, and that this caused a shift towards a more SFA profile.…”