22 November 1996

Fermentable energy query

By Jessica Buss

INCLUDING additional supplies of fermentable energy in grass silage-based cow diets increases milk yield, protein and caesin concentration. But the source of fermentable energy is insignificant.

Thats according to John Murphy, Teagasc researcher at Moorepark, Co Cork. He says initial studies using molasses showed a response in yield and protein that correlated with inclusion rate. However, it is not known if the response was due to the molasses, or the increase in dry matter intake from mixing molasses with grass silage (see table).

In the study, daily cow dry matter intakes increased from 14.8kg when no molasses was fed to 16.6kg with 5% molasses, 17.4kg with 10% molasses and 18.2 with 15% molasses. This was fed to four groups of cows receiving 5kg of concentrate that included sugar beet pulp, soyameal, rapemeal and maize gluten. Concentrate crude protein level increased as molasses inclusion rose.

A second study compared the effects of different fermentable energy sources – fibre, starch and sugar or a mix of all three. Cows were fed grass silage and 3kg of concentrate plus either 4kg unmolassed sugar beet pulp (fibre), 4kg barley (starch), 4kg molasses (sugar) or 4kg of a mix of the three.

"There was no difference between diets in the effect on milk protein," says Dr Murphy. "The mix gave the highest milk yield, but no additional benefit in milk composition."

With a poor response to starch contradicting other studies it appears that a high, but as yet unknown, level of starch is needed produce a milk protein response, claims Dr Murphy.

Additional supplies of fermentable energy in grass silage-based rations can increase milk yields, says researcher John Murphy.