The partition of insensible losses of body weight and heat from cattle under various climatic conditions

Abstract

A discrepancy exists between previously reported measurements of cutaneous moisture vaporization from cattle by methods involving direct weighing of the whole animal and measurements by 'sweat capsule' methods (McLean, 1963). In the preceding paper it was suggested that this discrepancy arises from unsuitable ventilation of the capsules used, and a technique was described by which the errors of the capsule method were held to a minimum. This paper describes experiments in which the capsule technique was employed simultaneously with a mask method for measuring respiratory losses and with direct measurements of total insensible weight loss. A comparison is made of the relative influences of the physical and physiological factors governing heat losses from cattle, and the limits of effectiveness of the various physiological adjustments to heat stress are assessed. METHODSThree Ayrshire bull calves, aged between 6 and 10 months, were used. Each was exposed on successive days in a climatic chamber (Findlay, McLean & Bennet, 1959) to air temperatures of 15, 20, 25, 30, 35 and 400 C, all at a vapour pressure of 8 nun Hg, and also to vapour pressures of 20 and 35 mm Hg at an air temperature of 350 C. These environmental conditions are hereafter referred to by the abbreviations 15, 20, 25, 30, 35L, 40, 35M and 35H, where L, M and H denote the low, medium and high humidity levels. The exposures were not necessarily on consecutive days, and the schedule of eight climatic conditions was applied three times to each animal. One animal was exposed to the complete schedule one extra time, because failure of the measuring apparatus had invalidated many of the earlier readings. Each exposure lasted approximately 4 hr and consisted of a 2 hr waiting period followed by a 2 hr period in which measurements were made. Following each exposure to the environment 35M each animal was kept in the climatic room for a further 3 hr.During this time the air temperature was maintained at the same level as before, but the air humidity was altered at 20 min intervals from the original level of 20 mm Hg to 26, 13, 34, 8 and finally back to 20 mm Hg. When not in the climatic chambers the animals were housed in an unheated byre. They were fed twice daily at 7 a.m. and 4 p.m. on a diet of 1X4 kg concentrates per day and in addition were offered hay and water ad lib. when in the

Latent heat loss of Holstein cows in a tropical environment: a prediction model

“…In contrast, under high temperatures the body can gain heat by convection (Gebremedhin & Binxin, 2001); if the environment is characterized by intense solar radiation the body gains large amounts of heat by radiation (Curtis, 1982). In those conditions the ability of the animal to withstand its environment is proportional to its ability to dissipate heat by evaporation from the skin surface as a result of sweating (Finch et al, 1982;McLean, 1963;Maia et al, 2005a) or from the respiratory system by panting (Stevens 1981;Maia et al, 2005b).…”

“…Zootec., v.37, n.10, p. [1837][1838][1839][1840][1841][1842][1843]2008 difference between the body surface and the environment (McLean 1963). In contrast, under high temperatures the body can gain heat by convection (Gebremedhin & Binxin, 2001); if the environment is characterized by intense solar radiation the body gains large amounts of heat by radiation (Curtis, 1982).…”

Studies on the nature of sweat gland ‘fatigue’ in the goat

“…The mean amount of sweat produced by each gland as assessed from Tables 1 and 3 was 0-013 #tl./hr. A similar calculation can be made of the secretary activity of a sweat gland in cattle, a bovid species in which sweating is the major means of evaporative heat loss (McLean, 1963c).…”

Perda de calor por evaporação cutânea associada às características morfológicas do pelame de cabras leiteiras criadas em ambiente tropical

“…Em elevados níveis de temperatura ambiente, a evaporação torna-se a principal via para a dissipação de energia térmica dos animais (Finch, 1985;Gebremedhin et al, 1981), a qual ocorre na superfície da epiderme, pela sudação (McLean, 1963b;Taneja, 1958Taneja, , 1959daSilva & Staling, 2003;Maia et al, no prelo), e no trato respiratório (Stevens, 1981;daSilva et al, 2002;Maia et al, 2005). Por outro lado, sob essas condições, a condução, a convecção e a radiação podem eventualmente tornar-se mecanismos de ganho de energia térmica, pois dependem diretamente da temperatura ambiente (McLean, 1963b;Gebremedhin et al, 2001;daSilva, 2000;Maia et al, no prelo).…”

“…Por outro lado, sob essas condições, a condução, a convecção e a radiação podem eventualmente tornar-se mecanismos de ganho de energia térmica, pois dependem diretamente da temperatura ambiente (McLean, 1963b;Gebremedhin et al, 2001;daSilva, 2000;Maia et al, no prelo).…”