Comparative effects of ASI and APR sire breeding values on the lactation profile of pasture-based Holstein-Friesian cows

Abstract

Estimated Breeding Values (EBVs) of bulls are useful indicators of the genetic transmission ability of an animal of desirable traits to their progeny. Lactation profile differs between different merit cows but for pasture-based production systems, the impact of emerging EBV evaluation methods remains largely unpublished. In this study, Wood’s incomplete gamma model (Y(t) = atbe−ct ) was utilised to compare the effects of the Australian Selection Index (ASI) and Australian Profit Ranking (APR) EBVs on the shape of the lactation profile of first-parity, pasture-based Holstein-Friesian cows. Initial yield and the rate of increase to peak were significantly influenced by EBV choice, although peak yield was not. It was concluded that Wood’s incomplete gamma function adequately modelled the lactation profile of pasture-based cows explaining over 90% of the observed variation irrespective of using ASI or APR sire breeding values.