Optimal mature size of angus cows for maximum cow productivity

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Abstract
Lifetime maternal performance records of 113 Angus cows born over a 12-year period were used to estimate the relationship between cow size characters, mature size (A) and maturation rate (K), and lifetime maternal performance characters, years in the herd (YH), number of calves (NC), total calf weight (TW), average calf weight at weaning (AW) and calf weight per year in herd (kg/year). Pertinent reproductive management of the herd was: heifers were mated to calve as 2-year-olds; any heifer failing to calve or any cow failing to wean a calf a second time was culled; all matings were to purebred Angus sires. Mean cow mature size was 487 ± 5 kg with a maturation rate of 0·058 ± 0·001. Means for maternal characters were: YH, 7·4 ± 0·4; NC, 6·4 ± 0·3; TW, 1283 ± 71; AW, 200 + 1·8; and kg/year, 173 ±5·1. The correlations between maternal characters and A and K, respectively, were: YH, −0·21, 0·15; NC, −0·21, 0·15; TW, −0·16, 0·12; AW, 0·20, −0·15; and kg/year, 0·05, −004. The regression of maternal characters on mature size was quadratic in every instance with optimal cow size for each character being: YH, 468; NC, 465; TW, 471; AW, 493; and kg/year, 475. The optimal cow size for average weight of calf weaned was 18 to 25 kg heavier than the optimal size for those characters associated with fertility. Relationships between maturation rate and maternal performance were not statistically significant.