28 July 1995

Controlling milk fat to suit the market

Straw can be fed to heifers, sucklers and dry cows when forage is scarce.

HIGH input dairy systems must deliver high milk yields with a high milk protein content, but with the option of varying fat content according to the demands of quota management or niche markets.

So said Dr John Sutton of the Centre for Dairy Research (CEDAR), University of Reading.

Speaking at a Royal Association of British Dairy Farmers open evening, Dr Sutton explained that milk fat originates from long chain and volatile fatty acids (VFA) produced in the rumen.

"In the future it may be possible to use antibiotic-based rumen modifiers to control fat," he said. "These have been shown to increase propionate, a VFA that also triggers insulin release, which in turn reduces milk fat."

"But, modifiers are not approved in the UK and so for now farmers must look at other ways to adjust milk fat," he said.

The most widely identified dietary factor is the fibre content of the diet.

"Reducing the acid detergent fibre content of the diet to below 20% of the total dry matter of the ration, will help reduce fat levels, but producers must take care because the cow, her rumen and milk fat contents are sensitive to low fibre diets," said Dr Sutton.

Instead of high fibre feeds, based on by-products such as maize gluten and sugar beet feed, he advised producers use high starch, cereal-based concentrates, and include feeds that have been shown to reduce fat content.

CEDAR has completed a three-year mixed forage trial, where one-third of grass silage, in a diet offering 6kg DM/day of concentrate, was replaced with fodder beet, brewers grains or maize silage. The results showed that all the alternative forages increased milk yield and protein but had varying effects on milk fat content.

Of the three, brewers grains reduced fat by 0.16% to 0.37% while fodder beet caused only minor changes. Maize silage reduced fat content by about 0.11% to 0.25% but only when included as 75% of the diet. When maize comprised only a third of the forage, it had little effect on fat content.

"Use of total mixed rations (TMRs), or out-of-parlour concentrate feeders, can also increase milk fat contents," said Dr Sutton.

"Though generally TMR and out-of-parlour feeding is good practice, it will sustain milk fat levels. This is because the cow consumes small, regular and consistent meals throughout the day which keeps the rumen pH constant.

"In contrast twice daily feeding of starchy concentrates will help to reduce fat levels," he said.

Dr Sutton said the choice of energy source in the concentrates was also important.

In a trial at CEDAR, 2kg of sugar beet feed included in a daily ration of 8kg concentrate and ad-lib silage increased the fat content of the milk by 0.34%. In comparison the use of 4.8kg barley dark grains with 3.2kg sugar beet feed, reduced milk fat by 0.46%.

Jonathan Riley

&#8226 Reduce acid detergent fibre content in diet to below 20% of total dry matter.

&#8226 Feed high starch concentrates instead of high-fibre by-products such as sugar beet pulp.

&#8226 Offer feeds shown to reduce milk fat such as maize silage (to replace grass silage), brewers grains, or barley dark grains.

&#8226 Give concentrates twice daily instead of spread over the day in a TMR or from out-of-parlour feeders.


CEDARtrials have shown that brewers grains reduce milk fat.