Reproductive performance of seasonal-calving, pasture-based dairy herds in four regions of New Zealand

AIMS: The primary objective of this study was to describe the reproductive performance of a selection of New Zealand dairy herds in 2009/10 and 2010/11. A secondary objective was to explore associations between a number of biophysical and socio-demographic herd-level variables and herd-level reproductive outcomes. METHODS: Seasonal-calving, pasture-based herds from the Waikato (n=16), Taranaki (n=16), North Canterbury (n=17) and South Canterbury (n=14) regions of New Zealand were enrolled as part of a larger study. Submission, conception and pregnancy risks ("in-calf risks") were calculated for 2009/10 and 2010/11 based on cow-level records and from the results of strategically timed pregnancy diagnoses. Additional herd-level information was collected during interviews with the herd key decision maker (KDM). Associations between independent variables and reproductive performance were examined using univariable and multivariable generalised linear models. RESULTS: Mean 6-week in-calf risk of the herds over both study years was 67 (min 46, max 86)%, mean 3-week submission risk was 81 (min 44, max 95)% and mean probability of pregnancy at first insemination was 48 (min 25, max 71)%. On univariable analyses, the herd's 6-week in-calf risk in the year before enrolment (2008/09) was the strongest identified predictor of each of submission risk, probability of pregnancy at first insemination and 6-week in-calf risk (all p<0.01), while other predictor variables considered were non-significant. From multivariable modelling, herds using extensive production systems had better reproductive performance than more intensively managed systems. Higher 3-week submission risks were achieved in herds where the KDM were farm managers rather than owner operators, and where the predominant breed was Jersey rather than Friesian. CONCLUSIONS: The New Zealand dairy industry has set a target for a mean 6-week in-calf risk of 78%, with minimal hormonal intervention, by 2016. Achieving this target appears unlikely unless there are substantial increases in both submission risks and pregnancy at first inseminations. The mean 6-week in-calf risk of New Zealand dairy herd does not appear to have changed in the last decade. However the large differences between herds indicate that better reproductive performance is currently possible in many herds. The herd's 6-week in-calf risk in the year before enrolment (2008/09) was the strongest identified predictor of current 6-week in-calf risk, suggesting that rate of improvement in reproductive performance would be slow within current management systems unless substantial changes are introduced.