Relationship of lifetime productivity with mature weight and maturation rate in Red Poll cows

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Abstract
Lifetime maternal records were collected from 116 Red Poll cows born over a 12-year period. Estimates of mature cow weight (A), maturation rate (K) and lifetime maternal performance characters (years in herd, YH; number of calves weaned, NC; total calf weight weaned, TW; total calf weight plus mature cow weight produced, TW + A; average calf weaning weight, AW; calf weight weaned per year in the herd, TWIYH and predicted cow metabolizable energy (ME) required per kg beef produced, MEITW + A) were calculated to study the relationship between cow growth characters and maternal performance. Calf weights were adjusted to a steer basis. Reproductive management practices consisted of breeding heifers to calve as 2-year-olds; cows failing to calve in two successive seasons were culled. Mean mature cow weight was 554 (s.e. 6) kg with a mean maturation rate of 0·059 (s.e. 0·001) per month. The correlation between A and K was −0·69. Means for lifetime maternal characters were: YH, 5·1 (s.e. 0·2); NC, 4·7 (s.e. 0·2); TW, 1187 (s.e. 54) kg; TW + A, 1741 (s.e. 55) kg; AW, 252 (s.e. 1·7) kg; TWIYH, 228 (s.e. 4·5) kg/year; and MEITW + A, 72 (s.e. 1·2) MJ ME per kg beef. The regression of maternal lifetime productivity measures on mature cow weight was quadratic for YH, NC, TW and TW + A with optimal cow weight being 606, 600, 605 and 628 kg, respectively. AW and MEITW + A were positive linear functions of cow mature weight. Regressions of YH, NC, TW, TWIYH and TW + A on K were negative linear functions. AW and MEITW + A were not significantly related to K.