29 November 1996

High-merit calves need quality rearing


By Sue Rider

DAIRY producers who fail to ensure high genetic merit heifers are well grown at calving risk reducing first lactation performance by 1000 litres.

This was the stark warning from Dr Sinclair Mayne of the Agricultural Research Institute of Northern Ireland, Hillsborough, speaking at a Dalgety/Holstein Friesian Society High Genetic Merit initiative meeting.

"Failure to rear these heifers correctly in their first lactation will severely limit the ability of the cow to express its genetic potential," said Dr Mayne.

They needed different management to the traditional British Friesian – but there had been no research on heifer rearing since the 70s. Guidelines on rearing Friesians were no longer appropriate for high merit animals.

"Traditionally heifers have not been calving at their mature weight with the expectation that, in addition to producing milk, they will continue to grow," he said. "But with the high merit animals higher drive to produce milk – an extra 11% of milk for every unit of feed energy – there isnt the potential for them to grow." It was, therefore, important that high merit heifers calved at heavier weights – about 600-620kg, he said. This would enable them to maximise their intake potential and guard against excessive weight loss in early lactation which could disrupt productivity and fertility.

Dr Mayne and a colleague, Dr Alistair Carson, had set out heifer rearing guidelines in a report Developing Improved Rearing Regimes for High Genetic Merit Dairy Herd Replacements published by Dalgety and HFS.

The authors recommended that rearers continue to aim for a calving age of 24 months. They stressed the need for calving higher genetic merit animals at 600-620kg lw instead of 520kg. Yet research had shown that it was important to to restrict growth during between 3-10 months.

"High levels of feeding with growth rates over 0.8kg/day during this critical stage have been shown to increase fat deposition in the udder while reducing the development of milk secretory tissue," said Dr Mayne. The risk of such difficulties appeared to be higher with fermented forages than with either concentrates or dried forages such as hay or straw," Dr Carson said.

"Grazed grass may also pose less of a threat in this respect.

"This may be due to the type of protein involved and needs further research if improved rearing regimes are to be developed."

Dr Mayne advsed an optimum level of protein in concentrates of 16-20% depending on forage type and quality. He also stressed that care must be taken in the two months prior to calving to ensure the heifer does not put on excess body fat which could cause calving difficuliteis.

By Sue Rider

DAIRY producers who fail to ensure high genetic merit heifers are well grown at calving risk reducing first lactation performance by 1000 litres.

This was the stark warning from Dr Sinclair Mayne of the Agricultural Research Institute of Northern Ireland, Hillsborough, speaking at a Dalgety/Holstein Friesian Society High Genetic Merit initiative meeting.

"Failure to rear these heifers correctly in their first lactation will severely limit the ability of the cow to express its genetic potential," said Dr Mayne.

They needed different management to the traditional British Friesian – but there had been no research on heifer rearing since the 70s. Guidelines on rearing Friesians were no longer appropriate for high merit animals.

"Traditionally heifers have not been calving at their mature weight with the expectation that, in addition to producing milk, they will continue to grow," he said. "But with the high merit animals higher drive to produce milk – an extra 11% of milk for every unit of feed energy – there isnt the potential for them to grow." It was, therefore, important that high merit heifers calved at heavier weights – about 600-620kg, he said. This would enable them to maximise their intake potential and guard against excessive weight loss in early lactation which could disrupt productivity and fertility.

Dr Mayne and a colleague, Dr Alistair Carson, had set out heifer rearing guidelines in a report Developing Improved Rearing Regimes for High Genetic Merit Dairy Herd Replacements published by Dalgety and HFS.

The authors recommended that rearers continue to aim for a calving age of 24 months. They stressed the need for calving higher genetic merit animals at 600-620kg lw instead of 520kg. Yet research had shown that it was important to to restrict growth during between 3-10 months.

"High levels of feeding with growth rates over 0.8kg/day during this critical stage have been shown to increase fat deposition in the udder while reducing the development of milk secretory tissue," said Dr Mayne. The risk of such difficulties appeared to be higher with fermented forages than with either concentrates or dried forages such as hay or straw," Dr Carson said.

"Grazed grass may also pose less of a threat in this respect.

"This may be due to the type of protein involved and needs further research if improved rearing regimes are to be developed."

Dr Mayne advsed an optimum level of protein in concentrates of 16-20% depending on forage type and quality. He also stressed that care must be taken in the two months prior to calving to ensure the heifer does not put on excess body fat which could cause calving difficuliteis.

High genetic merit heifers at Hillsborough are fed a high-quality, first-cut silage, supplemented with concentrates if necessary, to ensure target growth rates are achieved, says Dr Sinclair Mayne (inset). He insists that successful heifer rearing depends on jacking up management at all levels.


HEIFER GUIDELINES


&#8226 Calve aged 24 months

&#8226 Calving weight 620kg

&#8226 Growth rates under 0.8kg/day during critical 3-10 month stage

&#8226 Growth rates after 10 months can be increased to 0.9kg/day

&#8226 Consider basing diets on dried forages/concentrates

&#8226 Monitor condition in last two months of pregnancy to avoid overfat heifers and reduce calving difficulties.