27 March 1998

Breed for pasture

appetite

BREEDING high-yielding dairy cows may be inappropriate for pasture-based management systems if the increased nutrient requirements can only be met by increasing feed costs.

So Sinclair Mayne of the Agricultural Research Institute of Northern Ireland, Hillsborough told the grazing conference.

Dr Mayne believes breeding programmes should put greater emphasis on cow intake characteristics and factors affecting voluntary intake of grazed herbage to better reflect production.

Breeding should aim to increase farm profit by optimising the use of the resources available. But North American and Western European bloodlines have been selected under intensive, high input feed systems with little or no access to pasture.

"High genetic merit cows are not expressing as much of their potential on Irish low concentrate diets as they do on US farms where concentrate use is higher. The benefit of increased genetic merit is, therefore, lower in Ireland." But Dr Mayne is not sure how important it is for these animals to express their full genetic potential.

Higher genetic merit cows increase milk production by using more of their feed nutrients for milk production. On a given feed regime high merit animals sustain higher yields primarily from increased loss of body reserves and/or reduced rates of tissue gain. Coping with this increased body weight loss to maintain health, welfare and reproductive performance is a major challenge.

When the higher merit cow is able to meet her increased nutrient requirements through increasing food intake, such as by improving grazing management to capitalise on her hunger drive, then this should be pursued.

In addition, one study in by Teagasc at Moorepark, Fermoy, Ireland concludes that there is little re-ranking of proven bulls when split between high concentrate (1580kg a cow) and low concentrate (540kg a cow) herd management. This indicates that high merit animals perform better in both systems.

But response to increased concentrate use is 48% higher in high genetic merit cows than medium merit cows. This suggests high genetic merit cows are unable to eat enough feed in a higher forage diet to fuel the extra yield potential.

When concentrates are restricted high genetic merit cows eat more herbage but end lactation at a lower condition score. Liveweight loss is greatest in early lactation and also increases risks of infertility, he said. This would cause more concern in grazing herds that wanted a seasonal calving pattern, and poorer fertility of high merit cows should not be overlooked (see p50).

Producers need to decide whether to modify production systems to meet the cows potential or to breed cows that suit that system.

He suggests that a multi-trait selection index – such as the one used in New Zealand – which incorporates breeding goals for pasture based- production should be developed. In the mean time, he advises using sires with a reliable proof, whose daughters re breed well in pasture-based systems.

THERE may be a role for alternative breed in herds that rely on grazed grass for a high proportion of their diets, because they may be more fertile, said Sinclair Mayne.

He explained that a farm study by the Avonmore Waterford Group in the Republic of Ireland showed that Normande and Montbelliarde had better conception rate than medium or high merit Friesian cows.

All cows were spring calving with an average concentrate input of 590kg a cow and maximum reliance on grazed grass.

Montbelliarde cows averaged the same yield with higher milk quality as medium merit Friesians but the interval to first service was 5 days shorter, conception rate to first service was 48% compared with 35%, and conception rate to second service was 54% to compared to 41%.

High merit Friesians yielded highest with conception rates of 48% to first service and 25% to second service, while the Normande cows had lower yields, but conception rates almost equalled the Montbelliarde cows.

HIGHER MERIT?

&#8226 May not be suitable for grass-based systems.

&#8226 Grazing management may need altering.