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The Influence of Age, Sex, and Season of Birth of Calf, and Age of Dam on Preweaning Growth Rate and Type Score of Beef Calves

Virginia Agricultural Experiment Station, Blacksburg

Abstract

The purpose of this study was to evaluate the influence of age, sex, and season of birth of calf, and age of dam on the preweaning growth rate and type score of Virginia beef calves.

The study included 6,173 calves, divided into two groups for analysis. One group included 4,166 non-creep-fed calves and the other included 2,007 creep-fed calves. The data were pooled over a four-year period (1953–1956, inclusive) and over 44 Angus, 19 Hereford, and 3 Shorthorn herds.

The data were arranged into sets of normal equations, and least squares estimates of the various effects were computed.

No significant differences were apparent in the growth rate of non-creep-fed calves from 90 to 210 days of age. There was a slight decline from 211 to 240 days and a rather sharp decline after 240 days. Creep-fed-calves under 150 and over 240 days of age appeared to be at a greater disadvantage than non-creep-fed calves in those same age groups. Type scores were not influenced sufficiently by age of calf to be of any practical importance.

Sex of calf influenced growth rate significantly in both the creep-fed and non-creep-fed groups but had little effect on type score. Bull calves grew approximately 5% faster than steer calves, and steer calves grew approximately 8% faster than heifer calves.

Season of birth had a significant influence on growth of non-creep-feed calves, but was of no practical importance on growth of creep-fed calves or type score in either group.

Age of dam was the most important source of variation studied with the largest differences occurring among the younger age groups. Maximum production was obtained from cows in the six- to ten-year-old age group.

The reliability of the estimates was checked by applying them to the performance records of 3,147 non-creep-fed calves weighed in 1957. They were found to be satisfactory for equalizing sub-class means.