|dc.description.abstract||Quantification of the change in Friesian and Jersey sires’ estimated breeding values (eBVs) was carried out between their initial proof, reproof, and latest proof. Alongside the eBV change quantification, these three estimates of genetic merit were analysed to predict which provides the best estimate of the genetic merit that is passed onto the sires’ offspring. The study was based on data sourced from NZAEL New Zealand Dairy sire summaries. Each bulls’ initial proof, reproof, and latest proof eBVs were entered into an excel spread sheet and were sorted to only include CRV Ambreed and Livestock Improvement Company (LIC) Friesian and Jersey bulls born in New Zealand between 2000 and 2006, with eBV reliabilities greater than 96% in 2016; totalling 316 sires. The key traits analysed were milk protein, milk fat, milk volume, live-weight, fertility, and somatic cell count.
To evaluate which measurement provides the best estimate of a sire’s genetic merit that is transmitted to their offspring, the original 316 sires’ milk protein eBVs for the initial proof, reproof, and latest proof were compared to their son’s (total 1876) initial proof eBV for milk protein.
Sire eBVs for milk protein, milk fat, and milk volume declined between their initial and latest proof with an average decline of 6.36kg (43.1%), 8.22kg (53%) and 340.6 litres (70.1%) respectively. Jersey sires showed a greater decline in eBVs than Friesian sires for milk protein (7.97kg vs 5.2kg), milk fat (9.65kg vs 7.2kg), and milk volume (426 litres vs 280 litres). CRV Ambreed sires declined significantly less than LIC sires’ eBVs for milk protein (5kg vs 7.1kg), milk fat (6.4kg vs 9.3kg), and milk volume (300 litres vs 364 litres). Sires’ initial proof, reproof, and latest proof all had a strong correlation to that of their son’s initial proof, 84%, 84% and 85% respectively.
The findings of this study highlight the decline in New Zealand’s elite Friesian and Jersey sires estimated genetic merit over their life time, and poses factors potentially causing this decline.||en