360. Reactions to hot atmospheres of Jersey cows in milk

Abstract

Four grade Jersey cows 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 and erythro-cyte composition of the blood; milk volume and butterfat content; behaviour.Rectal temperature rose to higher values with less ready establishment of equilibrium the hotter the condition, but exceeded 107° F. only in the hottest atmosphere. (Dry-bulb temperature 110° F., absolute humidity 16 gr./cu.ft.)Respiratory rate was similarly and markedly affected. In both cases, humidity had a marked effect as well as temperature, an increment of 0–4 gr./cu.ft. (approx. 4%) in humidity having the same effect as 1° F. rise in air temperature. The highest average respiratory rate was 200/min. Respiratory minute volume rose less than the rate, so that tidal volume was reduced.Pulse rate was essentially unaffected by a rise in temperature but tended to rise somewhat with humidity.Evaporative loss was markedly increased by temperature, much less so by humidity. Increased pulmonary ventilation was inadequate to account for the observed losses, which are attributed to sweat-gland activity.Behavioural changes included some licking, panting, salivation, mild agitation, cessation of rumination and refusal of water. Weakness and staggers did not occur under these conditions.Neither milk nor butterfat production was essentially affected by the exposures. Blood calcium and phosphate levels fell, but the erythrocyte count was unchanged.These findings provide basic data with which subsequent observations under varying conditions can be compared.