Effect of Environmental Temperature and Dietary Fat on Growth and Physiological Responses of Newborn Calves

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Abstract
Effects of cold environmental temperature and supplemental dietary fat (energy)on growth rate and physiological responses of young dairy calves fed a milk replacer diet were studied. Thirty-six Holstein bull calves were randomly assigned to one of six treatment allotted in a 2(-4.degree. C or 10.degree. C) .times. 3(10, 17.5, or 25% dietary fat) factorial arrangement of treatments Calves began the experiment at an average of 6 d of age and received .6 kg dry milk replacer in 4 L of water daily for wk. Average daily gains (kg/d) over the 3-wk trial for calves fed 10, 17.5, and 25% fat diets were -.04, .02, and .09 at -4.degree. C and .15, .22, and .20 at 10.degree. C. Gains were signficantly lower for calves housed at -4.degree. C. Rectal temperatures were lower for calves at -4.degree. C than at 10.degree. C and for calves fed 10% versus 25% fat diet. Respiratory rates and water intakes were lower for calves housed at -4.degree. C but were not affected by diet. Concentrations of plasma glucose and prolactin were lower for calves housed at -4.degree. C while concentrations of plasma free fatty acids and growth hormone were not affected by temperature. Plasma free fatty acids were increased by dietary fat, and plasma growth hormone was reduced as dietary fat increased. Calves housed at -4.degree. C had higher maintenance energy requirements (.133 Mcal metabolizable energy/kg.75) than calves housed at 10.degree. C (.101 Mcal metabolizable energy/kg.75). Consequently, calves housed at -4.degree. C require 32% more energy for maintenance than calves housed at a temperature within their thermoneutral zone.