CORRELATED RESPONSES IN RATE OF MATURATION AND MATURE SIZE OF COWS AND STEERS TO DIVERGENT SELECTION FOR YEARLING GROWTH-RATE IN ANGUS CATTLE

Curves were fitted to data from Angus cattle selected for high or low growth rate from birth to yearling. The data consisted of weight (n = 284) and height (n = 160) data of cows from birth to weaning of their calf as a 4-year-old, and weight, height, length and girth of steers f rom birth to four years of age (n = 22). Mature weight (kg) and height (cm) of cows were 540 +/- 6 and 119.3 +/- 0.7 for the High line, 497 +/- 6 and 115.7 +/- 0.6 for a randomly bred line, and 418 +/- 6 and 10 8.3 +/- 0.6 for the Low line. Mature weight and height of High line co ws reared by Low line dams were 556 +/- 12 and 122.1 +/- 1.1, while th ose of Low line cows reared by High line darns were 459 +/- 11 and 111 .9 +/- 1.0, indicating part of the difference between High and Low lin es was attributable to poorer maternal environment provided by Low lin e dams. Mature weight, height, length (cm) and girth (cm) of steers fr om the High line were 765 +/- 19, 135 +/- 1, 178 +/- 2 and 233 +/- 3, while steers from the Low line were 591 +/- 21, 121 +/- 1, 159 +/- 2 a nd 215 +/- 3. No significant difference between lines was found in rat e of maturation of weight, height, length and girth. There were no sig nificant maternal effects on rate of maturation of weight or height of cows. After scaling to remove genetic differences in mature size, the High line matured significantly faster than the Low line for weight, height, length and girth. The results indicate that selection for year ling growth rate leads to a change in size at all ages, but temporal p attern of maturation is not altered. (C) 1998 Elsevier Science B.V. Al l rights reserved.