361. Reactions of Jersey calves to hot atmospheres

Abstract

Four grade Jersey calves were exposed for 7 hr. twice a week to each of several atmospheres having dry-bulb temperatures ranging from 85 to 110° F. and absolute humidities ranging from 6 to 16 gr./cu.ft. The following reactions were studied: rectal temperature; pulse rate; respiratory rate; respiratory volume; evaporative loss; calcium, phosphate, sugar and erythrocyte composition of the blood; behaviour.Rectal temperatures rose rapidly to a higher level than was shown by cows under similar conditions, but maintained a steady equilibrium thereafter, except under the most severe conditions.Respiratory rate responses resembled those of rectal temperature, the difference from those of cows being even more striking.Humidity had relatively less effect upon the rectal temperature and respiratory rate responses of calves than of cows.Pulse rate and tidal respiratory volumes were relatively unaffected, but minute respiratory volumes rose.Evaporative loss per unit body weight resembled that of cows, except that humidity again had less effect. Pulmonary ventilation was inadequate to account for the observed losses.Behavioural changes resembled those of the cows but weakness of the hind limbs was observed at rectal temperatures above 106° F. Blood calcium, phosphate, sugar and erythrocyte levels were not essentially affected.Possible explanations for the lower thermal tolerance of calves, as compared with cows, are considered.

Sweating in cattle. I. Cutaneous evaporative losses in calves and its relationship with respiratory evaporative loss and skin and rectal temperatures

“…On the other hand, in the Shorthorn a rise in air temperature accompanied increased cutaneous evaporation and skin temperature. As suggested by Robinson & Klemm (1953) the ability of the Zebu cross to maintain nearly constant temperature and subsequent increase in cutaneous evaporation may be due to sweating.…”

“…Cutaneous evaporative loss in cattle and the increase in this loss under hot conditions has been measured by a number of workers (Rhoad, 1940;Riek & Lee, 1948a, b;Kibler & Brody, 1950;Thompson, McCroskey & Brody, 1951;Robinson & Klemm, 1953;Knapp & Robinson, 1954;Klemm & Robineon, 1955). The results of this study confirm these earlier findings.…”

“…Robinson & Klemm (1953) observed that for efficient sweating in cattle one would find no rise or perhaps even a fall in skin temperature when the sweat glands were active. Knapp & Robinson (1954) stated that a typical drop in skin temperature at the onset of sweating was not detected in Jersey cows exposed to rising air temperatures, because ruminants secrete only a limited amount of sweat for evaporation.…”

“…In cattle the role of moisture supplied by the sweat glands for heat dissipation is not clearly understood. Cutaneous water losses in cattle and the increase in this loss under hot conditions has been measured (Rhoad, 1940;Riek & Lee, 1948 a, b;Robinson & Klemm, 1953;Thompson, McCroskey & Brody, 1951;Kibler &Brody, 1950 ;Knapp& Robinson, 1954;McDowell, Lee & Fohrman, 1954;Klemm & Robinson, 1955). These estimates are higher than would be expected from diffusion-moisture alone.…”

“…There is no doubt that cattle skin is abundantly supplied with sweat glands (Gurlt, 1835;Ellenburger, 1906;Muto, 1925;Kelley, 1932;Yamane & Ono, 1936;Findlay & Yang, 1950;Dempsey, 1946;Carter & Dowling, 1954;Dowling, 1955). However, the activity of sweat glands has been a subject of great controversy.…”