CORRELATED RESPONSES IN CALF BODY-WEIGHT AND SIZE TO DIVERGENT SELECTION FOR YEARLING GROWTH-RATE IN ANGUS CATTLE

Correlated responses in calf weight and size traits resulting from 17 years (1974-1991) of divergent selection for yearling growth rate in a n Angus beef cattle experiment were evaluated. Deviations of two diver gent selection lines (High line and Low Line) from an unselected Contr ol line, as well as trends in estimated breeding values (EBVs) in the selection lines were examined. Correlated responses per year for birth weight, weaning weight, and weight, height, girth, length, pelvic are a and scrotal circumference at yearling age were 0.18, 1.53, 2.23 kg, 0.35, 0.47, 0.29 cm, 1.06 cm(2) and 0.12 cm, respectively, for the Hig h line, and -0.24, -1.71, -2.41 kg, -0.29, -0.29, -0.41 cm, -0.83 cm(2 ) and -0.05 cm, respectively, for the Low line. The changes in EBVs af ter 17 years for birth weight, weaning weight and yearling weight were 1.52, 18.36 and 30.70 kg, respectively, for the High line, 0.40, 1.35 and 2.88 kg, respectively, for the Control line, and -2.85, -15.40 an d -27.07 kg, respectively, for the Low line. These correlated response s, which were large enough to allow for 90% correct discrimination bet ween the two divergent selection lines based on body size, occurred wi thout any changes to the body shape of the animals. Realised genetic c orrelations of these traits with yearling gain were all positive and r anged from 0.24 to 0.97. These results indicate that selection for yea rling growth rate in beef cattle was effective in changing the genetic potential for size up to yearling age. (C) 1997 Elsevier Science B.V.