Improving the reliability of fertility breeding values in Australian dairy cattle.

Over several decades, a decline in fertility in dairy cattle has been observed around the world. Breeding values, known in Australia as ABVs were implemented for fertility in 2003 using a single trait model for calving interval and since then the genetic trend in fertility ABVs appears to have stabilised. In April 2013 a new fertility ABV calculated using a multi-trait model was introduced that includes the following predictors of 6 week in-calf rate: calving interval, lactation length, days to first service, non-return rate and pregnancy rate. The new multi-trait fertility model has increased the reliability of fertility ABVs (compared to the single-trait model it replaced) for bulls born since 2000 by 6.5% and 7.6% for Holsteins and Jerseys respectively. The limitation to realising the full potential of this model is the capture of data. For cows that have calving interval records, 93%, 28%, 21% and 24% have records used for lactation length, days to first mating, pregnancy result and non-return to first service used in ABV calculations (for records collected between 2008 and 2010). The Dairy Futures CRC in conjunction with ADHIS have recently embarked on a co-ordinated effort to capture many more mating and pregnancy records that are electronically recorded on-farm but currently do not contribute to fertility ABVs. We have also set up a genomic reference population of females through identifying herds that have very well recorded data. The introduction of genomic data has been shown to increase the reliability of fertility ABVs of first proof bulls by a further 3%, having a genomic reference population will aid in sustaining the reliability of fertility ABVs. The collection of extra phenotypic data in addition to genomics is expected to increase the response to selection in fertility in the Australian dairy herd.