Effect of environmental temperature and dietary fat on growth and physiological responses of newborn calves.

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 treatments allotted in a 2(-4 degrees C or 10 degrees C) X 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 3 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 degrees C and .15, .22, and .20 at 10 degrees C. Gains were significantly lower for calves housed at -4 degrees C. Rectal temperatures were lower for calves at -4 degrees C than at 10 degrees C and for calves fed 10% versus 25% fat diet. Respiratory rates and water intakes were lower for calves housed at -4 degrees C but were not affected by diet. Concentrations of plasma glucose and prolactin were lower for calves housed at -4 degrees 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 degrees C had higher maintenance energy requirements (.133 Mcal metabolizable energy/kg.75) than calves housed at 10 degrees C (.101 Mcal metabolizable energy/kg.75).(ABSTRACT TRUNCATED AT 250 WORDS)