Reproductive inefficiencies and opportunities in dairy and beef cattle in Australia

Reproductive performance is a key driver of the economics of dairy and beef breeding herds. In the absence of hormonal treatment to induce or stimulate lactation, regular parturition and initiation of lactation are key events directly affecting the average daily milk production of dairy herds, culling decisions and farm gross margins. Thus efficient reproductive management is a critical prerequisite for sustainable dairy production. Economic modelling of the performance of both southern and northern Australian beef cattle breeding enterprises has demonstrated that cows which recommence cycling and readily conceive in response to the annual seasonal improvement in pasture quality and quantity return the greatest gross margin per hectare. The major factors affecting the weaning rate in beef breeding herds are interval after calving to resumption of normal ovulations, embryo-foetal survival and perinatal survival. Additional keywords: reproductive performance, beef, dairy cattle, factors affecting Introduction In Australia, dairy and beef cattle breeding herds are located in a wide range of environments from the tropics to temperate regions. In 2006 there were 2.79 M dairy cattle with about 77% of these in the temperate and subtropical regions of Victoria and New South Wales (ABS 2005), in areas of either moderate rainfall and or access to irrigation water for pasture production. Breeding of dairy cows in year-round calving herds is mainly by artificial insemination (AI), and in seasonal calving herds a combination of AI followed by bull mating is used. The majority of dairy cattle in Australia are Holstein-Friesians. In contrast to the dairy industry, in 2006 there were 26.1 M beef cattle in Australia with over half of the breeding herds in northern Australia, and all herds using natural mating with only very limited use of AI. Beef production systems range from intensive improved pasture to very extensive native pasture grazing systems. In northern Australia, 85% of beef cattle have some Bos indicus content (Farquharson and Banks 2002) whilst in southern Australia the majority of cattle are of Bos taurus origin. Regardless of the production system, reproductive inefficiencies have a significant effect on herd and farm profitability. In dairy herds, economic modeling (Morton, 2001) has demonstrated that modest improvements in reproductive performance, e.g. improvements in 6-week in-calf rate in seasonal calving herds from 60% to 65%, and in 100-day in-calf rate in year-round calving herds from 41% to 53%, could increase annual gross farm income by $6,000 and$10,000 per 200 cows, respectively. Recent data by Best (2007) from central Queensland indicated that lifting weaning rates from 65% to 75% increased gross margins per adult equivalent (AE) from $118 to $140 in store steer systems and $150 to $170 in Brigalow breeding properties, assuming in both cases that breeder mortalities were 2%. This paper will review the reported magnitude of reproductive inefficiency in dairy and beef breeding herds, the factors which significantly contribute to sub-optimal reproductive performance, and highlight strategies which may be used to reduce the risk of these factors adversely impacting on herd performance. The beef component of this review is biased towards the northern Australian beef industry as this reflects the experience of the authors. Reproductive performance in dairy and beef herds Dairy cattle The Dairy Australia-funded InCalf Project conducted in the mid-‘1990’s used a population approach to define achievable levels of reproductive performance for seasonal (n=124) and year-round calving (n= 43) herds, and quantified the herd-, cow-, and insemination-level factors significantly affecting the reproductive performance of Australian dairy herds (Morton and McGowan, 2002). The measures developed by InCalf (www.incalf.com.au) which accurately define the efficiency of reproduction in seasonal calving dairy herds are 6-week-in-calf-rate (6wk ICR – proportion of cows which conceive within 6weeks of the planned start of mating), and in year-round calving herds 100-day-in-calf-rate (100-day ICR – proportion of cows which become pregnant by 100days after calving; these cows will have intercalving intervals of ≤12.5months). Taking the median performance of the 25% of herds with the highest overall measure of reproductive performance InCalf has defined achievable levels of performance for Australian seasonal calving (6wk ICR of 71%) and year-round calving herds (100-day ICR of 58%). The key drivers of 6wk ICR and 100-day ICR are submission rate (SR – the percentage of cows submitted for mating in the first 3 weeks of the mating period or within 80 days of calving in seasonal and year-round calving herds, respectively) and conception rate (CR – the percentage of inseminations/matings which results in