An interdisciplinary study of maternal productivity in beef cattle.

Maternal productivity, defined as weight of cow-calf output per unit of feed consumed on an annual basis is complex with many component traits interacting with on-farm management to determine overall production efficiency. This thesis implemented an interdisciplinary research approach that integrated qualitative social science and quantitative animal science to examine the output components of maternal productivity. Such an approach generated an understanding about factors associated with maternal productivity from both an animal science perspective and also as perceived by seedstock breeders. The initial qualitative research revealed divergence in seedstock breeder‟s perspectives on topics associated with maternal productivity. Specifically, attitudes to animal management with regard to grazing management, cow energy reserve fluctuation and the utilisation of fat reserves were varied. Breeder‟s attitudes on these topics were associated with divergence in perspectives on the importance of selection for production traits including yield, growth and milk compared with selection for perceived resilience traits including subcutaneous fat and earlier maturity pattern. The outcomes from the initial qualitative research drove the analysis of animal performance data collected through the Cooperative Research Centre for Beef Genetic Technologies Maternal Productivity Project. These analyses included understanding • the repeatability of cow body composition traits • associations of Breedplan EBVs with cow energy reserves • genetic correlations between cow body composition traits, • associations between genetic merit, nutrition and cow body energy reserves with reproductive rate Objectively measured body composition traits had moderate to high between time repeatability. In addition, Breedplan EBVs for EMA, Rib, Rump (P8) and IMF were closely related to the equivalent ultrasound measure in Angus and Hereford cows at pre-calving and weaning in the first two parities. Breedplan carcass EBVs were not associated with cow body composition change during lactation. Together these results indicate that currently available Breedplan carcass EBVs change cow body composition, and that selection for increased fatness at a young age will result in cows that are fatter. Cow body composition traits were moderately heritable and had high to very high between time genetic correlations indicating that at the genetic level, cow body composition traits are genetically very similar across time (pre-calving and weaning) and age (first and second parity). P8 and Rib EBV and pre-calving P8 and rib fat depth were associated with several components of reproductive rate with varying effects depending on parity, calving season and nutrition. The importance of genetic and phenotypic fatness on reproductive rate was larger in autumn calving and low nutrition production systems. Breeders viewed results presented on associations between reproductive rate and EBVs and energy reserves as unsurprising and also as supporting their varied perspectives and current selection direction. In addition, weighting of EBVs in a selection index was associated with variance in calving rate. The implications of these results are that the varied selection emphasis by breeders involved in this project may be appropriate. Relationships between lifetime cow maternal productivity, supply chain profitability, on-farm production system and genetic merit need to be addressed to enable beef breeders to make informed animal selection and management decisions. By working closely with livestock breeders, and listening to, and understanding their observations, perspectives and beliefs on maternal productivity, and also in analysing animal performance data, there has been considerable benefit in generating a greater understanding of the production system and the interactions that occur within it. The outcome of this approach has been to firstly demonstrate and explain the varied perspectives held by seedstock breeders on associations between genetic merit and maternal productivity; and secondly, using animal performance data demonstrate how and why many of the observations and contrasting perspectives of breeders appear justified.Thesis (Ph.D.) -- University of Adelaide, School of Animal and Veterinary Sciences, 201