BODY DIMENSIONS AND CARCASS MEASUREMENTS OF CATTLE SELECTED FOR POSTWEANING GAIN FED 2 DIFFERENT DIETS

Genetic and phenotypic parameters among nine body dimensions and two measures of growth rate were estimated from measurements on 709 Angus and Hereford bulls and heifers born in 1984 and 1985. Height and width at hips, height at withers, body length, girth, head length and width, muzzle width, and cannon bone circumference were measured at weaning and again after 168-d postweaning gain tests. The cattle were from the final two calf crops of a 20-yr study to examine the response to selection for postweaning gain when fed either a high-concentrate diet or an all-hay diet. Sources of variation included year of birth, breed, sire within breed, diet, age of dam, and the linear regression on calf age. Parameter estimates among the body dimensions and carcass measurements were also calculated using a subsample of 318 Hereford and Angus bulls fed until they achieved greater-than-or-equal-to 7 mm of subcutaneous fat. Yearling measurements from calves fed the high-concentrate diet were larger than those from calves fed the all-hay diet. Sire within breed, age of dam, and the regression on age of calf affected all measurements (P < .001) at both measurement times. Dietary energy concentration influenced all body measurements taken at the end of test. Heritabilities of all body measurements were moderate to high. The highest genetic correlations with gain were for cannon bone circumference, body length, and heart girth. The heritabilities of all body dimensions were sufficient to indicate that selection progress was possible, but the low genetic correlations with gain and carcass traits suggested that this may not be desirable.