22 March 1996

Higher quality – by design

How can dairy rations be manipulated to secure designer milk of specified fat and protein content? Jessica Buss reports on the latest research findings

MILK quality can be manipulated precisely and consistently to meet milk buyer specifications by feeding readily available concentrates.

This is the finding of research at ADAS Bridgets Dairy Research Centre, Martyr Worthy, Hants.

ADAS nutritionist Rosemary Mansbridge claims proteins ranging from 2.8 to 3.55% have been produced in its high yielding herd.

"Proteins have proved more difficult to change than fat," she says. "This is because we know less about how protein is produced. In contrast work on manipulating fat was done 20 years ago and is well documented."

Factors other than feeding that can influence milk quality include breeding but this strategy is too long term given the changing milk market. Stage of lactation, calving season, feeding system and herd structure can also affect quality.

Bridgets work aims to keep these factors constant and to use cows yielding over 30 litres a day to represent future production levels.

Contracts for protein

Increasing either by-pass starch, using ground maize grain, or by-pass protein, using protected soya- bean, fed to cows will increase milk protein % without affecting fat %, claims Miss Mansbridge. When both types of feed were offered at an optimum level the maximum milk protein % achieved on a grass silage diet was 3.55%.

"But milk yield and total protein yield drops on the highest level of by-pass starch. So, on a liquid contract which pays for kg of fat and protein, the optimum level of by-pass starch is lower," she says.

These increases in milk protein % using vegetable sources of digestible undegradable protein worked without boosting milk ureas.

"It is only too easy to increase protein in milk by feeding urea. But this produces milk higher in non-protein nitrogen, which is not beneficial to cheese making.

"It is important to maintain the casein level of milk, typically 77-78% of milk protein. Cows fed both by-pass starch and by-pass protein in our studies produce more protein at the same average casein content," she says. There was also no effect on milk urea levels. Healthy milk for the future

Milk containing high levels of beneficial polyunsaturated fat and lower levels of saturated fat, which increases the risk of heart disease, has been produced at the centre. This has been achieved by feeding cows naked oats, whole soyabeans and processed rape cake. A dramatic effect on milk fat % was also seen with the naked oats.

"Naked oats contain higher level of oil than ordinary oats and the oil is predominantly unsaturated. But oats comprise only 10% total oil compared with whole soya-beans and processed rape cake. So more naked oats had to be fed to deliver the high oil quantities needed." At 8.5kg of naked oats in the diet milk fat % decreased by 25% compared with cows fed 0.8kg of the protected fat Megalac.

Cows fed 3.5kg full-fat soya gave the highest level of polyunsaturated fats, while cows fed 4kg of processed rape cake produced the highest levels of monounsaturated fat.

Semi-skimmed milk

Milk containing 1.8% butterfat can be produced, without ill effects on feed intake or yield, in under four weeks by including fish oil in the diet, according to recent Bridgets MAFF-funded research.

Miss Mansbridge claims this low-fat milk is also higher in the beneficial long-chain type polyunsaturated fats. These are preferred by human nutritionists but normally almost non-existent in milk.

"There was no difference in dry matter intakes between different diets, although these were slightly low for all groups, at 17 to 19kg a day. Milk yields of 34 to 36kg and protein levels were unaffected by feeding fish oil – only milk fat was reduced. There were no signs of any health issues such as poor rumen function or lameness that could cause concern," she says.


WHATS NEEDED


&#8226 Feed by-pass starch and by-pass protein to secure high protein milk.

&#8226 Produce low-fat milk by feeding naked oats.

&#8226 Produce very low-fat milk by feeding fish oil.

&#8226 Healthy milk low in saturated fats is produced by feeding whole soyabeans or processed rape cake.

Research at ADAS Bridgets seeks to determine how to manipulate rations to fine-tune fat and protein. Above: Rosemary Mansbridge: "Proteins have proved more difficult to change than fat."