Abstract

Selection to change age at puberty over 23 years was monitored in Angus cattle in a Ruakura study. A foundation herd was divided in 1984 into four lines: a control unselected line, and lines selected for high age-at-puberty (Age+), low age-at-puberty (Age-), and high scrotal circumference (SC), with the last two lines being merged later. Age at puberty (first oestrus, AFO) was determined in heifers from observations of first behavioural oestrus date; puberty was determined in bulls from SC records from 8 to 13 months of age. Selection for AFO was applied mainly to bulls, using the genetic correlation between AFO and SC from our data (-0.25 ± 0.09). Puberty records from 6,473 weaned calves were analysed, using restricted maximum likelihood methods to determine genetic changes achieved by line. Realised heritability estimates were 0.26 ± 0.03 (standardised AFO), and 0.40 ± 0.04 (individual SC records; repeatability over ages, 0.68 ± 0.01). Averaging over recent year's data, Age- line heifers had lower AFO than Age+ line heifers by 69 days (19%; 1.33 phenotypic standard deviations), and bulls had larger SC by 3.0 cm (9.9%; 1.17 phenotypic standard deviations). Correlated responses in pregnancy rate favoured Age- over Age+ females at all ages.

NC, Amyes, and CA Morris

Proceedings of the New Zealand Society of Animal Production, Volume 69, Christchurch, 201-205, 2009