Responses of Holstein Calves Raised on Limited Milk to Simulated Louisiana Summer Climatic Conditions

Abstract

One group of five female and one group of four male newborn Holstein calves were subjected to air temperatures cycling diurnally between 75 and 95F and constant vapor pressure of 20mm Hg in a psychrometric chamber and two similar groups were subjected to ambient winter climatic conditions in an open-air calf barn until ages ranging from 60 to 90 days. During the post-experimental period from 91 to 150 days of age, all calves were placed together in a cool environment and group fed.Conditions imposed on the experimental calves were stressful and resulted in greatly depressed growth rate, which continued during the post-experimental period. Limited water allowances made the thermal stress more acute. Consumption of concentrates and hay was reduced in the experimental calves and the digestibilities of dry matter, energy, crude protein, and total digestible nutrients were not significantly lower than in the control calves.Faster respiration rates and higher rectal temperatures and lower hematocrit and hemoglobin levels were found in the experimental calves as compared to those of the control calves. No direct effects of heat exposure on plasma carotenoid or vitamin A levels nor on serum protein concentration were evident. There was some indication that heat stress decreased serum α-globulin.