13 November 1998

Unbalanced diets put high merit cows at risk

By Jeremy Hunt

LIFETIME health and productivity of high genetic potential dairy cows will be put at serious risk where they are fed unbalanced diets containing too much concentrate and too little fibre.

Although maize is widely used as a silage and considered a fibre constituent, the crops high grain proportion must not be underestimated in rations.

"Maize can easily throw things out of balance because of the 40-50% grain inclusion it brings to rations," says USA ruminant nutritionist Limin Kung of Delaware University.

Dr Kung, who is recognised internationally for his research work on forage, is concerned that UK dairy farmers may fall foul of some of the problems encountered on USA dairy farms. These were as a result of increased use of lower priced cereals in cow diets at the expense of forage.

"USA dairy farmers have been using a lot of by-products, many of them forage-type by-products with high fibre levels. Farmers did not expect them to pose any dietary risks, but the small particle size of these forages presented serious problems in the rumen.

"On paper the fibre content looked good, but it was a different story when this material reached the cows digestive system."

Farmers who are not taking professional advice on ration formulation and who are trying to unlock more output from high genetic merit cattle using a greater inclusion of concentrates, must keep a close eye on cow health and be aware of the high risk of acidosis.

"Genetics are pushing up production and cows expected to sustain annual yields of 11,000kg of milk have to be managed to a high standard in terms of overall health and rumen function," says Dr Kung.

Producers must recognise that as yields increase it will become more challenging in terms of their management input.

"Researchers like myself have no quick-fix solution to this; to exploit high yields and sustain them is not going to be easy but it has to be tackled head-on."

RATION BALANCE

&#8226 High grain proportion in maize.

&#8226 Too much concentrate, too little fibre?

&#8226 Balance vital as yields increase.