11 September 1998

Danger in high energy feed replacements

REDUCING energy deficit in high yielding dairy cows, which occurs naturally after calving and through to peak lactation, can significantly improve fertility, but some high energy feeds are less suitable than others.

Claire Wathes, professor of reproduction at the Royal Veterinary College, told delegates that fats were commonly used in post-calving rations to ensure high energy intakes when a cows appetite is usually suppressed.

But excessive levels of polyunsaturated fatty acids (PUFAs), such as those derived from linseed, fishmeal and soya, can upset rumen fermentation and suppress intakes.

Some PUFAs have a negative effect on reproduction, such as suppressing level of prostaglandin, which is essential for embryo development, warned Prof Wathes. Which PUFAs were at fault and their exact effect on reproduction was not known, she said.

The effect of dietary protein on fertility is clearer. "High levels of dietary protein are associated with reduced pregnancy rates, particularly in older cows," she said.

"Rumen undegradeable protein passes through the abomasum and small intestine to provide amino acids for maintenance and reproduction. Rumen degradable protein breaks down in the rumen, increasing ammonia and urea levels in blood, both of which have negative effects on reproduction.

"It will be some time before we fully understand what happens and why," said Prof Wathes.

Fats affect reproduction warned Claire Wathes.