Genetic parameters for female fertility traits in New Zealand dairy cattle have been estimated using a data set of herds participating in the Livestock Improvement Sire Proving Scheme. In total, 66294 records of both pure and crossbred Friesian, Jersey and Ayrshire cows in their first lactation were used. The highest heritability estimates were .134, .058, .037, .037, .029 for age at calving (AC), interval from start of mating (STOM) to first mating (SMFM), interval from STOM to conception (SMCO), pregnancy rate at day 21 or 42 after STOM (PR21) or (PR42), respectively. Low heritabilities were obtained for first mating to conception (FMCO), calving interval (CI) and number of services (NS) (<.017). Genetic correlations between CI and either SMFM or SMCO where high (.920 or .957). Genetic correlation between SMCO and PR21 or PR42 is close to one. Therefore the later three traits are identical from the selection point of view. For AC, genetic and phenotypic correlations with milk production traits were high and unfavourable. Antagonistic genetic correlations also existed between milk yield and the fertility traits and between SMFM, SMCO, FMCO or NS and fat or protein yield. The unfavourable genetic correlations between milk production and fertility traits strongly suggest that fertility performance should be incorporated into the breeding objectives of New Zealand dairy cattle. Based on their heritability estimates, their genetic coefficients of variation and their genetic correlations with production and other fertility traits, it is recommended that SMFM and PR21 (or its more easily obtainable equivalent trait 2-to-24-day non-return rate, 2-24NRR) should be used as selection criteria. In addition, the incidence of use of treatment programmes for overcoming fertility problems, such as induction of calving and anoestrus treatment, should also be incorporated into the selection index.
Proceedings of the New Zealand Society of Animal Production, Volume 56, , 38-41, 1996
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