The objective of the present study was to investigate the suitability of various fertility traits for describing the reproductive performance of dairy cows in New Zealand. Using a data set from herds participating in the Livestock Improvement Sire Proving Scheme over the 1986/87 to 1992/93 seasons, the following female fertility traits have been investigated. Based on the start of mating (STOM) in a particular herd, the intervals from STOM to first mating (SMFM) and to the successful mating (SMCO) were calculated and compared to the internationally used traits that are based on the calving date, such as, calving to first mating (CFM) and calving to successful mating (days open, DO). Further traits considered are age at calving (AC), number of matings per conception (NS), first to successful mating (FMCO), calving interval (CI) and two traits that indicate whether a cow became pregnant within 21 or 42 days of STOM (PR21, PR42). The traits defined for the unique conditions in New Zealand, SMFM, SMCO, PR21 and PR42 emphasize the economic importance of reproduction to dairy production. The comparison to overseas studies using DO, FMCO and CI showed that New Zealand dairy cows had a better fertility performance than overseas cows.
Proceedings of the New Zealand Society of Animal Production, Volume 56, , 27-31, 1996
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