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Attainment of puberty and response to superovulation in performance-tested Simmental heifers
Published online by Cambridge University Press: 02 September 2010
Abstract
Puberty during performance test and the effect of reproductive maturity and performance on test on superovulatory response were investigated using Simmental heifers.
Three generations of Simmental heifers (no. = 110) were performance tested for beef characteristics between 23 and 49 weeks of age over 3 years successively. Embryo recoveries were performed at 52 and 61 weeks of age following the end of the performance test. The onset of puberty was observed in 26 of 30 (87%) heifers in the 3rd year. The mean age at puberty was 284·7 (s.e. 6·63) days. Age at puberty was not significantly related to daily live-weight gain (1·5 (s.e. 0·02) kg) up to the onset of puberty. Heifers experienced zero to six oestrous cycles before initiation of the first superovulatory treatments. There was a non-significant tendency (P > 0·05) for heifers that were not cyclic to produce the highest yields of viable and grade 1 embryos at the first embryo recovery.
Performance test characteristics recorded were: total food intake (1604·0 (s.e. 13·2) kg), total energy intake (1852·0 (s.e. 169·0) MJ metabolizable energy) and live-weight gain (263·9 (s.e. 2·2) kg) during test; live weight (486·5 (s.e. 31·5) kg), backfat depth (5·6 (s.e. 15) mm) and muscle score (9·6 (s.e. 0·10) units) at the end of test and estimated breeding value for the selection index (+£7·00 (s.e. 0·76)). These were used as independent variables in general linear models to study their relationship with various measures of superovulatory response. Recovery rate of ova and embryos; and the yields of viable and grade 1 embryos were not related to any aspects of performance on test.
In conclusion, superovulation and embryo recovery were affected by reproductive maturity at the time of gonadotropin treatment and these procedures may be more effective in juvenile heifers before the establishment of cyclicity. Embryo production from 12- to 15-month-old Simmental heifers following a beef performance test was not related to their performance on test.
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- Copyright © British Society of Animal Science 1996
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