High merit heifers put on muscle but not fat
High merit heifers put on muscle but not fat
By Jessica Buss
Heifer rations high in digestible undegradable protein will give high growth rates needed for higher genetic merit stock to achieve target weight at calving without them putting on too much body condition.
Thats according to Cogent vet Stewart Scott who aims to calve 650kg heifers at 23-24 months old and at a condition score of 3-3.5. They should then milk well and get in calf again without having to grow and gain condition during their first lactation, he explains.
"Heifers must also have good muscles – there is some evidence that milk protein comes from muscle protein. A good potential to produce protein from muscle growth saves having to feed for it later."
Roy Eastlake, nutritionist for Somerset and Avon Silage, has designed the heifer rations at Cogent to provide 15-18% crude protein. Diets must also encourage rumen fill, so 70% of the DM is forage.
To achieve the ideal calving weight donor heifers must grow at 0.9kg/day, says Mr Eastlake. He believes there is little evidence to support the need to restrict growth rates before puberty with high genetic merit stock provided they are on a high protein diet. For that reason the growth of embryo donors at Cogent is not restricted. But recipients are only targeted to grow at 0.75kg/day from three to 14 months, so that they can be flushed with a higher energy diet to improve pregnancy rate. They are flushed for four weeks before service, and until confirmed eight weeks in calf, when growth rates are 1.2kg/day.
The recipients, managed as normal breeding heifers, are fed a 55% DM diet, with 18% crude protein. Currently, this includes 8kg grass silage, 1kg straw, 1kg maize gluten, 1kg High Pro soya and minerals.
For flushing 1kg a heifer of sugar beet pulp is added to the ration to increase the energy density and reduce the crude protein.
"Producers will achieve returns from these rations through better growth and fertility," he says.
Cogents Stewart Scott… rations have been altered to stop heifers putting on too much body condition.