25 December 1998

Index link to specific requirements might increase uptakes

CUSTOMISED genetic indexes tailored to farm requirements for specific markets, breeds or inputs may help encourage uptake.

According to SAC researcher Jennie Pryce, a frequently asked question is whether bulls tested on a high-input system perform as well on a low-concentrate system.

In a trial looking at how extremes performed, researchers in Canada, where inputs are high, and New Zealand, where inputs are low, swapped cows to study how their different genetics performed in opposite countries.

Cows were found to perform best at home, in circumstances for which they were selected, she said.

But when changes in inputs were less extreme bulls performed almost to expectations. In an Irish study there were minor changes to bull rankings when sires were re-ranked according to two levels of concentrate feeding which were about 1t different.

In the UK, performance of bulls daughters on high and low inputs was investigated in SACs Langhill herd, she said. "For every unit rise in genetic merit for fat and protein production, cows on higher inputs produced 0.2kg more milk, but on the lower-input system cows produced just 0.13kg more milk.

"On lower inputs cows cannot produce their genetic potential, possibly because they do not eat enough or their index is a better interpretation of genetics on a high-concentrate diets." Most bulls are progeny tested in high-concentrate systems.

Breeding decisions are long-term and it is possible that in future cow diets with a relatively high forage content may be more cost-effective, she added.

But sire rankings could differ between systems and it may be necessary to breed bulls for the different systems. Research at Langhill will continue to investigate breeding strategies which increase emphasis on feed intake rather than tissue loss to fuel future increases in yield.

Customised indexes could build on PLI, with numbers and traits varying to suit different circumstances, said Dr Pryce.