CORRELATED RESPONSES TO SELECTION FOR YEARLING OR 18-MONTH WEIGHT IN ANGUS AND HEREFORD CATTLE

Correlated responses to selection for yearling (AS1 herd) or 18-month weight (AS2 herd) were evaluated against a control (AC0 herd) in a progeny test herd using 2294 calves born in 1975-1988. A sample of privately-owned Angus bulls, available by artificial insemination (AI), were compared with them for eight liveweight or gain traits up to 18 months, with four carcass traits on steers. Cows of known pedigree in the progeny test herd were also evaluated for seven maternal traits. Other correlated responses were evaluated directly in the AC0 and selection herds (three puberty traits, daily food intake, cow weight, and survival and reproduction traits). Realised genetic correlations to selection for yearling weight (AS1 herd) averaged 6% higher (for growth and carcass traits) than published paternal half-sib estimates, whilst those with 18-month weight (AS2 herd) were about 10% lower than with yearling weight. The sign of maternal genetic effects for live weights up to weaning varied among selection herds. Realised genetic correlations with selection weight averaged 0.51 (carcass fat depth), 0.93 (food intake), 0.16 (scrotal circumference in bulls), 0.18 (age at puberty) and 0.37 (weight at puberty in heifers), 0.38 (cow weight, AS1 herd) and 0.92 (cow weight, AS2 herd). The selection herd differences from control were not significant for cow or calf mortality or reproductive traits (6501 mating records), but tended to be negative for cow and calf death rates, and variable for overall reproductive rate.