Abstract #522

# 522
Definition and implementation of a breeding value for feed efficiency.
Jennie E. Pryce*1,2, Oscar Gonzalez-Recio1, Gert Nieuwhof1, Bill Wales1, Michael P. Coffey3, Ben J. Hayes1,2, Michael E. Goddard1,4, 1Department of Economic Development, Jobs, Transport and Resources, Bundoora, VIC, Australia, 2La Trobe University, Bundoora, VIC, Australia, 3SRUC, Edinburgh, Midlothian, UK, 4The University of Melbourne, Melbourne, VIC, Australia.

The objective was to describe how a new estimated breeding value (EBV) for feed efficiency is calculated. From April 2015, the Australian Dairy Herd Improvement Scheme (ADHIS) has published a new breeding value, called feed saved, that is the amount of feed saved through improved metabolic efficiency and reduced maintenance requirements. The breeding value includes a genomic component for residual feed intake (RFI) combined with either a genomic or pedigree EBV for body weight (BW) predicted using conformation traits. The RFI component of the feed saved EBV has 2 parts: Australian calf RFI and Australian lactating cow RFI. Genomic breeding values for RFI were estimated in a multi-trait analysis (3 traits) that included including Australian growing heifer and lactating cow RFI in addition to overseas (UK and Dutch) lactating cow RFI. The reference population included 50k single nucleotide polymorphism (SNP) genotypes and phenotypes for 234 Australian lactating cows and 843 heifers (approximately 6 mo old) and 958 UK and Dutch lactating cows. In all cases, the RFI phenotypes were trait deviations that were calculated by correcting dry matter intake for bodyweight, growth and yield (in the case of lactating cows). Effects for each SNP were calculated from the output of genomic best linear unbiased prediction and used to predict breeding values of 4,416 sires that were genotyped, but did not have RFI phenotypes themselves. These bulls already had BW breeding values calculated from type traits, from which maintenance requirements in kg of feed per year were inferred. Finally, RFI and the feed required for maintenance (through BW) were combined to construct a feed saved breeding value. Animals with EBVs that are one standard deviation above the mean are predicted to eat 65 kg dry matter less per year at the same level of milk production. The mean reliability associated with the feed saved breeding value was 0.37 in the data set of 4416 genotyped Holstein sires. From April 2015, feed saved has also been included as part of the Australian national selection index published by ADHIS.

Key Words: feed efficiency, residual feed intake, genomic