The effect of liveweight change on reproductive performance in a seasonally calving, pasture fed dairy herd

Abstract

This was a prospective cohort study of 930 lactations in 595 mixed aged dairy cows that calved between 1 July and 24 October of 2008 and 1 July and 24 October 2009 in a single dairy herd in the lower North Island of New Zealand. Parametric accelerated failure time models based on the log-normal distribution were used to identify and quantify the effect of factors influencing the time it took for cows to conceive after the Planned Start of Mating (PSM) date. A focus of this study was to quantify the effect of liveweight change in the first 4weeks after calving (δLWPP) and liveweight change in the period from PSM-21days to PSM (δLWBPSM) on PSM to conception intervals.Parity, calving to PSM interval, δLWBPSM, milk protein percentage, breed, clinical mastitis, the presence of a fertility treatment and season was associated with PSM to conception intervals. PSM to conception intervals for cows with zero or positive δLWBPSM was 74% of those for cows with negative δLWBPSM (TR 0.74, 95% CI 0.48 to 1.00; P=0.05).The findings of this study are consistent with those reported in the literature and better define the impact of long- and short-term liveweight changes on reproductive performance, providing the opportunity to design feeding programmes to minimise the impact of LW loss (used as a proxy for negative energy balance) on reproductive failure in pasture fed dairy herds. © 2012 Elsevier B.V.