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 m easures of growth rate were estimated from measurements on 709 Angus a nd 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 sele ction for postweaning gain when fed either a high-concentrate diet or an all-hay diet. Sources of variation included year of birth, breed, s ire within breed, diet, age of dam, and the linear regression on calf age. Parameter estimates among the body dimensions and carcass measure ments were also calculated using a subsample of 318 Hereford and Angus bulls fed until they achieved greater-than-or-equal-to 7 mm of subcut aneous fat. Yearling measurements from calves fed the high-concentrate diet were larger than those from calves fed the all-hay diet. Sire wi thin breed, age of dam, and the regression on age of calf affected all measurements (P < .001) at both measurement times. Dietary energy con centration influenced all body measurements taken at the end of test. Heritabilities of all body measurements were moderate to high. The hig hest genetic correlations with gain were for cannon bone circumference , body length, and heart girth. The heritabilities of all body dimensi ons were sufficient to indicate that selection progress was possible, but the low genetic correlations with gain and carcass traits suggeste d that this may not be desirable.