21 November 1997

GENETIC MERIT BEST WAY TO HIGH YIELDS

BREEDING higher genetic potential cows is the best route to maximise yield potential.

So said John Oldham of SAC Edinburgh at a conference held by Dairy Research and Consultancy (DRC), Reading. That was despite progress achieved through breeding being slow, with a 4.1 litres a cow a day increase in yield after 20 years.

This was the gain in yield achieved in studies at SACs Langhill Farm that has run high and low merit selection lines on high and low concentrate feeding regimes for 20 years.

High merit cows now have a PTA95 of 70kg fat and protein with the lower merit cows at 0kg fat and protein. Diets were fed in three steps based on stage of lactation and included grass silage and a distillery by-product.

"Langhills high merit cows produce as much milk on 1-1.5t less concentrate than their lower merit contemporaries," said Dr Oldham. These higher merit cows did not use feed more efficiently, but ate more when the system of feeding allowed and used more body condition to support lactation.

On the low concentrate feeding regime intakes were restricted because higher merit cows could not eat much more grass silage than lower merit animals – DM intakes averaged 15.7 and 15.2kg respectively.

The realisation of their genetic advantage was constrained, therefore, compared with cows fed a more digestible diet that was higher in concentrate, when intakes averaged 18.3 and 17.6kg DM for high and low merit cows respec-tively.

Increasing concentrates to higher genetic merit cows was more worthwhile, with these cows achieving an extra 5.3 litres a day yield when fed 2-2.5t of concentrate compared with those fed 1t of concentrate. Increases in yield achieved through breeding and feeding were additive, he explained.

"To achieve the genetic advantage you must feed cows," he says.

High merit cows produce as much milk but on less cake, says John Oldham.