Linear body measurements of cattle before and after 20 years of selection for postweaning gain when fed two different diets.

At weaning and again after postweaning gain tests, height and width at hips, height at withers, body length, girth, head length and width, muzzle width, and cannon bone circumference measurements were obtained from Angus and Hereford bulls and heifers born in 1964, 1984, and 1985 (n = 989). The cattle were from the initial and final two calf crops selected for postweaning gain when fed either a high-concentrate diet or an all-hay diet. Analysis of variance and canonical discriminant analysis were used to examine the relationships among body measurements and major sources of variation (breed, year of birth, sire within breed and year, diet, sex of calf, age of dam, and the regression on age of calf). Canonical discriminant analysis indicated that one underlying variate explained nearly 90% of the total variation among the weaning measurements, whereas three variates were required to account for that proportion in the end-of-test measurements. At both measurement times, the first canonical variate was associated with year of birth, the second with sex of calf, and the third with dietary energy. Correlations between each canonical variate and the original body measurements indicated that year of birth (variate 1) was most closely associated with body length and cannon bone circumference at weaning and with body length and height at hips (but not withers) at end of test. Sex of calf (variate 2) was associated most closely with width of muzzle and head. Diet (variate 3) was associated with heart girth. Faster-growing cattle were longer in body, but not necessarily taller.