A review of thermal stress in cattle

Abstract

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.

Transition milk or milk replacer powder as waste milk supplements to cold-stressed neonatal Holstein dairy calves: Effects on performance, feeding behavior, and health

“…As a result, when temperatures stray from this optimal range, it can impact calf behavior and physiology in various ways. These include increased energy expenditure to maintain warmth, decreased activity levels to minimize heat loss, the instinct to seek shelter, and the tendency to huddle together with other calves for warmth [ 64 , 65 ]. All those changes can potentially impact growth rates and overall health [ 66 ].…”

Hypothalamic Neuromodulation of Hypothermia in Domestic Animals

“…Releasing thyroid hormones from the hypothalamus promotes heat production by increasing the metabolic rate [1]. In cattle, environments with a −15 • C temperature increase metabolic activity by 35% due to their increasing thyroxine levels [53]. Moreover, mild hypothermia (35 • C) in rats increases their plasma levels of corticosterone and thyrotropin-releasing hormone while their prolactin levels decrease [54].…”

The welfare of ill and injured feedlot cattle: a review of the literature and implications for managing feedlot hospital and chronic pens

“…This interacted with the Health Domain, as cattle with BRDC may have impaired pulmonary capacity (97). Since cattle in high environmental temperatures thermoregulate via evaporative cooling (95), this may inhibit their ability to cool their body (98). The open-mouth breathing observed during the pen check (which was not observed in other steers in the pen) suggested that Physical Environment and Health Domains were impacted, and the associated mental effect of thermal discomfort, overheating, and breathlessness, which is considered a significant animal welfare issue (99), were impacting the steer's welfare.…”