The metabolism and thermal regulation of calves in the first month of life

Abstract

The object of these experiments was to examine the effect of environmental temperature on the energy exchange of the calf during its early life and, in particular, to determine the environmental temperature below which heat production increases in response to increasing cold. This latter temperature is called the critical temperature. The range of temperature between the critical temperature and that higher environmental temperature when heat production increases is called the thermoneutral zone. There is evidence that the mortality and morbidity of calves is greater in winter than in summer and is greater in the more northern and hence colder parts of Britain (Withers, 1952). This evidence suggests, but does not prove, that cold conditions in calfhouses are undesirable. Most farmers concur in their opinion that calves require a warm environment in early life, but no quantitative information about the conditions optimal for their growth and well-being is available. E X P E R I M E N T A L Animals andfood. Four Ayrshire bull calves (A, B, C and D) were used as experimental animals. They were given either 4 1. or 6 1. cow's whole milk each day in two meals. The milk was always given at body temperature. Experimental measurements began on or shortly after the 2nd day of life and continued for about 4 weeks. Sequence of experiments. Each calf was kept throughout the experiments in a respiration chamber, and measurements of metabolism were made at environmental temperatures of about 3', 13' and 23'. Initially, measurements were restricted to periods of 12 h because the calves had not learned to drink from a bucket and the chamber had to be opened to feed the calf. Once the calves had learned to drink, 24 h periods of measurements were used with the exception that with calf A all experiments were of 12 h duration. T h e details of all experiments are given in Table I. I n addition, on six occasions with calves C and D, heat production was measured at hourly intervals during the cooling of the chamber, over periods of 8-9 h, from temperatures of from over 30' to 3'. With the same two calves, rectal, skin surface and hair surface temperatures were measured throughout all experiments. The losses of energy in the faeces and the urine of calves B and D were measured when they were given 4 1. and when they were given 6 1. milk and the heat of combustion of the milk