Diurnal Variation in Weight and Rates of Shrink of Range Cows and Calves

Abstract

Cow-calf pairs were weighed on successive mornings to determine the effects of time on total weight. Early morning weights of mature Hereford/Angus crossbred cows were approximately 2.5% less than late morning weights in both the spring and summer. Weights of suckling calves were not significantly different between early and late morning. Linear regression analyses indicated drylot shrink weights of cows were primarily a function of length of time of shrink. Rate of weight loss was approximately 1% every 3 hours after an initial 3 hour loss of 3.5%. Secondary factors were status of cow (dry or wet), relative humidity (%), season (spring or summer) and initial cow weight. Shrink rates were slightly greater for wet cows than dry cows; when relative humidity was low; during spring; and for lighter weight cows. Rates of shrink of calves were primarily related to size of calf with calves weighing less than 53 kg (117 lb) gaining weight and calves weighing more than 53 kg losing weight.