The impact of declining dairy fertility on calving patterns and farm systems: A case study from northern Victoria, Australia

Fertility is crucial for pasture-based seasonal calving dairy herds, where cows are expected to calve in a single cohort at a time when peak milk production coincides with maximum pasture availability. However, dairy fertility has declined globally, and many Australian herds now use a split calving system, where non-pregnant cows are given additional opportunities to conceive by having two mating periods per year. Other factors prompting a move to split calving may include financial incentives for producing out-of-season milk, increasing levels of concentrate feeding, and pressure due to extreme seasonal conditions – all of which are particularly apparent in the northern Victorian irrigation region.The aim of our study was to describe the fertility and herd characteristics of the study population and to examine changes in reproductive performance and calving systems that have occurred over the same period.Our study population included 38 herds from the northern Victorian irrigation region in Australia. We collected individual cow records from each herd from the date on which they started herd recording (with a median start year of 2000 for mating event data) up until December 2016, comprising both fertility-related data such as insemination records, calving dates, and pregnancy test results, and systems-related data such as production, herd size and calving pattern.From a relatively small number of herds, we were able to obtain a dataset comprising 438,578 mating and pregnancy test records for 86,974 cows. From 2003 to 2016, 6-week in-calf rate and first service conception rate declined in the study population for both Holstein-Friesians and Jerseys, while 3-week submission rate remained unchanged. At the same time, the proportion of split calving herds in our cohort markedly increased, with a significant expansion in herd size compared to their seasonal counterparts. The proportion of first parity heifers in herds also increased, which may be a function of increasing herd size, or involuntary culling due to poor fertility.Split calving represents a significant system change for herd managers, with concomitant effects on labour management, input costs, and the lifestyle they experience. However, if this change has been implemented due to poor fertility without considering whether the increased income outweighs increased input costs, then a suboptimal decision may have been made. Finally, high quality data remains underutilised on individual farms, with significant benefits to the Australian dairy industry if we can overcome the numerous challenges to access it.