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Environmental Influences on Growth Rate and Grade of Yearling Beef Cattle^1,2,3,

Virginia Polytechnic Institute, Blacksburg

Abstract

The purpose of this study was to estimate the magnitude of several environmental influences on continuous growth and grade of yearling cattle of the Angus and Hereford breeds. There were records on 1,485 Angus bulls, 2,093 Angus heifers, 1,262 Hereford bulls and 1,394 Hereford heifers in the study. The effects of herd, year, age of dam, month of birth, age of animal and pre- and postweaning management practice were independent variables, where lifetime ADG and grade were dependent variables. The data were analyzed by least squares procedures.

Not only did herds and years significantly affect growth and grade in all analyses, but age of dam and age of animal were also significant sources of variation on growth in all breed-sex groups and on grade in most groups. Yearling cattle out of young dams had the slowest lifetime growth rate, whereas those out of mature dams (6 to 11 yr. old) had the fastest growth rate. Also, short yearlings (10 to 13 months of age) had the fastest growth rate with growth rate decreasing in each successive age group. In contrast to its effect on ADG of weanling calves, month of birth appeared to have no significant influence on ADG of yearling cattle. Creep feeding as calves significantly increased the lifetime ADG of yearling Hereford cattle, and the kind of postweaning treatment used had a significant effect on ADG of all groups, except Angus bulls, with growth rate being higher for the better fed animals.

Even though grade of yearling cattle was significantly affected by some of the independent variables, the effects were in no case large enough to be of practical importance.

¹ This paper is part of a thesis submitted by the senior author in partial fulfillment of requirements for the degree of Master of Science.

² Published with the approval of the Directors of V.P.I. Research Division and the Animal Husbandry Division, A.R.S., U.S.D.A., in cooperation with the Southern Regional Beef Cattle Breeding Project S-10.

³ The authors express their sincere appreciation for the data provided by the Beef Cattle Research Station, Front Royal; Virginia Forage Research Station, Middleburg; Virginia Beef Cattle Improvement Association, Blacksburg; and Bland Correctional Farm, Bland, Va.