Reproduction was compared in 2, 13-month weight-selection herds, Hereford (HS1) and Angus (AS1), in an 18-month weight-selection Angus line (AS2) and in an unselected Angus control (AC0), with ages at first joining in both sexes being 14, 14, 26 and 26 months respectively. Pregnancy rates (all ages, 5453 joinings) averaged 86, 88 and 90 and 86% respectively, so that yearling bull mating and/or weight selection have not disadvantaged the AS1 or AS2 lines. Sub-fertile bulls in the 3 selection lines numbered 5, 1 and 5 out of 59, 59 and 59 respectively. Calf death rates from 2-year-old AS1 heifers were lower than from 3- year-old first-calving AC0 heifers. The AS2 line weaned an adjusted total of 1005 calves (963, before adjusting by proportionally) from all age groups over 10 years, compared with 1239 calves in the AS1 line, a shortfall of 18.9%.

HR, Tervit

Proceedings of the New Zealand Society of Animal Production, Volume 43, , 179-182, 1983
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