Reproductive performance is an important factor contributing to on-farm efficiency and profitability. The purpose of this study was to define and quantify a set of fertility phenotypes for 352 Friesian-Jersey crossbred heifers, and determine key factors contributing to these indicators. Heats were observed and recorded prior to herd start of mating, and CIDRs were used to treat non-cycling heifers (51) once mating started. Progesterone samples were collected twice weekly, and luteal activity was identified where concentrations were >0.9 ng/ml for blood and >3.0 ng/ml for milk samples. Commencement of luteal activity was defined by either one elevated sample (CLA1) or two consecutive elevated samples (CLA2). For untreated heifers, the average intervals to CLA1 and CLA2 were 29.6 days (sd=14.3) and 34.1 days (sd=16.9) respectively. Other phenotypes were evaluated for conception and intervals to first heat, first service and successful service. Significant relationships were established between body condition score (BCS) at calving and the intervals to CLA. For every unit decline in BCS at calving there was an increase of 7.4 days to CLA1 and 8.8 days to CLA2. The evaluated fertility phenotypes, and their key contributing factors will be used in another study to identify related quantitative trait loci (QTL).

KM, Sanders, R Bennett, and R Spelman

Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 132-137, 2004
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