27 November 1998

Nutrient know-how cuts energy deficits

BETTER understanding of how nutrients are broken down and divided between maintenance and production is needed to avoid energy deficits in dairy cows after calving and associated health risks.

Chris Reynolds, of Reading University, says there is no reason for cows to mobilise body fat reserves post calving. This can cause illness such as Ketosis or fatty liver. Instead cows should eat more.

It is now accepted that dry matter intakes must increase post calving to sustain milk production. But more research is required to predict response to nutrients within rations that result in actual production, warns Dr Reynolds.

Cows must be fed as individuals as theres a huge variation in response to nutrient imbalance around calving. "Even modest-yielding cows can lose over 38kg of body fat in early lactation, according to US studies," he says.

One way to reduce energy demand is feeding more concentrates to reduce milk fat by increasing flow of trans fatty acids (TFAs). Although simplistic, this practice had its risks. "TFAs must not end up in milk. This would be an own goal with implications for human health."

A possible solution is to feed more by-pass protein to reduce reliance on body fat reserves. But it is economically unsound, particularly when the milk price is low, says Dr Reynolds. "We must address the nutritional imbalance and avoid crashes in feed intake which result in a massive increase in body fat mobilisation."

Whilst acknowledging ration models for early lactation cows needed refining, Dr Reynolds says research must focus on evaluating feeds as a source of nutrients to establish what is available to the cow in greater detail. &#42