A selection experiment at Waikite (Rotorua) began in 1971 with closed Angus herds selected for adjusted 13-month weight (AS1), adjusted 18-month weight (AS2) or with random replacement (ACO). A closed Hereford herd, selected for adjusted 13-month eight (HS1), was also established. At both 13 and 18 months of age, annual responses in live weight in the AS1, HS1 and AS2 herds averaged 0.96, 0.62 and 0.48% of the ACO herd means (calvings 1972-85). Five correlated responses were estimated. 1. Cow weight: From all ages of cows recorded over 4 seasons (on average 11 years of selection completed), AS1 and AS2 cows were 7.5 and 8.2% heavier respectively than ACO cows; HS1 cows were 2.5% heavier than AS1 cows, the same margin as in 1971. 2. Maternal weaning weight: (AS1 and AS2 herds only, relative to ACO): responses was estimated in a tester herd from calvings in 1982-86. The maternal grandsires were selected AS1 and AS2 bulls born after almost 2 generations (6 years) of selection. The AS1 herd was superior by 8.6 kg (5.7%) and the AS2 herd by 2.2 kg (1.5%). 3. Scrotal circumference: From the 1982-85 crops, the AS1 and AS2 bulls had respectively 0.9 (P<0.01) and 0.3 cm larger circumferences at 13 months of age and 0.7 (P<0.01) and 0.4 cm below corresponding AS1 values. 4. Height at withers: AS1 and AS2 bulls from the 1981 calf crop were respectively 3.5 and 2.5 cm taller (P<0.05) than the ACO bulls; the HS1 bulls were 2.3 cm taller (P<0.05) than the AS1 bulls. 5. Food intake: Average intake of silage by Angus bulls from the 1980 and 1981 crops were 10.4% and 11.7% greater (P<0.01) for AS1 and AS2 than ACO cattle respectively. Expressed relative to body weight, there was no significant difference due to herd. The pooled regression of daily intake of dry matter on 18-month weight was 0.0091 kg/kg (P<0.05), with a correlation of 0.32. The correlations of pre-fasting plasma tryptophan and the fall in plasma tryptophan concentration with average previous intake were 0.50 and 0.41, for bulls fasted over a 48 h period.
Proceedings of the New Zealand Society of Animal Production, Volume 49, , 165-170, 1989
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