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Some Nongenetic Influences on Calf Performance¹

Virginia Polytechnic Institute, Blacksburg

Abstract

Data were collected and analyzed to estimate the magnitude of some known nongenetic sources of variation on growth and conformation of beef calves and to compare two procedures for estimating age-of-cow effect. Sources of variation included were age, sex and month of birth of calf, year of record, age of dam and weaning.

All major effects studied had a significant influence on both growth and conformation. These effects are of sufficient magnitude to justify the use of correction factors in most instances.

Adjusting ADG and grade for differences in age of calves does not appear to be justified, if calves are weighed and graded within the ages of 150 to 240 days. These limits can be extended to 120 to 270 days if selection is based on an index combining ADG and grade.

Bull calves grew about 7% faster than steer calves, which in turn grew about 6% faster than heifer calves. These differences were somewhat larger when all calves were creep fed. Grades of bull and heifer calves were not significantly different, but both were significantly higher than grades of steer calves.

Calves born during February through May gained about 4% faster than January and June calves, 12% faster than July through October calves and 6% faster than November and December calves. Year effects were highly significant but differed for the two breeds.

Cow's age had a significant (P<.01) influence on calf gains and grades in both breeds regardless of the procedure used. Calves from cows under 7 years of age and over 11 years grew slower and graded lower than calves from 7- through 11-year-old cows. There were no significant differences among the 7- through 11-year-old cows. The effect on grade was considerably less than on gain and of little practical importance. Both procedures gave essentially the same results for Angus cattle and only minor differences for Hereford cattle.

¹ Published with the approval of the Director of the Virginia Agricultural Experiment Station.

² Professor of Animal Science, Beef Cattle Extension Specialist, and Graduate Assistant, respectively, Animal Science Department, Virginia Polytechnic Institute, Blacksburg.