22 March 1996

CEDARsays amino acids key to protein

AMINO acid supply may hold an important key to increasing milk protein production without a corresponding increase in yield or fat.

That is the claim of David Beever, CEDAR, University of Reading. "But we do not yet know which amino acids are needed. Many may be involved," he says.

Prof Beever says that feeding extra dietary protein often results in an increase in milk yield and protein yield such that protein content changes are small.

But good quality, rapidly degradable carbohydrates for rapid protein synthesis, such as Sodagrain, will also increase milk protein. CEDAR studies have shown that both Sodagrain and rolled wheat can increase protein by up to 0.3%. The highest response was to Sodagrain – probably because more can be included in the diet, he says. "For grass silage diets that are high in fibre but lack readily available sugars and starches, adding molasses increased protein from 3.2 to 3.5% in Danish studies.

"So quickly digested carbohydrates alongside diets of digestible fibre balanced with molasses or wheat will give a protein response. Fodder beet will also do this because it supplies readily fermentable carbohydrates. But fodder beet also stimulates milk fat, which may not be desirable."

High levels of maize silage included in the diet can also increase protein content. But he warns that both wheat and maize silage also reduce milk fat %.

Reductions in milk fat, for example from 4.2 to 3.9%, can be achieved simply by feeding brewers grains or distillers grains, says Prof Beever.

But a fair amount is paid for fat on many milk contracts and the margin from milk fat should not be ignored, although it is likely to be dependent on milk quota, he warns. John Sutton, also of CEDAR, claims milk fat levels can be controlled by manipulating the fibre, starch and sugar content of the feed or by adding fats or oils.

Dr Sutton adds that feeding reduced fibre depresses milk fat. This can be achieved by replacing grass silage in the diet with maize silage or reducing the amount of forage.

When fibre levels are below 20%, fat falls dramatically. At such low fibre levels it is difficult to fine-tune for fat, and the risk of rumen acidosis and poor cow health may be increased.

Feeding high starch concentrates such as cereals also works to reduce milk fat. But for the best effect these feeds must be offered twice a day. This will reduce both milk fat and protein, he stresses. &#42

David Beever: "Sodagrain and rolled wheat can lift protein by up to 0.3%."