15 January 1999

Nutrition not to blame for increased cow infertility

Manipulating livestock diets

to benefit health, fertility

and behaviour were key topics

at last weeks University of

Nottingham Feed

Manufacturers Conference.

Jessica Buss reports

WHILE feeding can manipulate hormones, so improving cow fertility, nutrition is rarely the cause of poor reproductive performance.

Phil Garnsworthy of University of Nottingham, told last weeks Feed Manufacturers Conference that recent research had found an interaction between the hormone insulin and ovarian activity.

In his study, cows were fed two diets, one stimulating insulin production and one producing less insulin. Insulin production could be manipulated through the supply of starch and fat, he said.

Preliminary results show that more cows fed the high insulin producing diet ovulated within 50 days of calving. Diet can, therefore, improve fertility performance. "If we had more research about nutritional influences on metabolic hormones affecting ovarian activity, it could be included in least-cost rationing programmes," said Dr Garnsworthy.

Infertility is often blamed on a negative energy balance when cows are producing high yields. That is because of low dry matter intakes leading to cows using their body reserves to support production.

But there were many additional factors affecting fertility, he warned. Those include health, genetic selection – which has focused on high yields, coincidentally resulting in poorer fertility – and a move to larger herds with less labour to focus on heat detection and timing of AI.

He argued that cows controlled their own intakes, dictating their own negative energy balance. "Fatter cows at calving lose more condition in early lactation."

Condition score at calving or service had little effect on conception rates unless it was below 1.5, he said. But when cows lost more than 1.5 condition score units between calving and service, conception rates fell, indicating disease or lameness concerns.

National herd fertility was reported to have declined, but nutrition had improved, so why blame nutrition for the rise in infertility, asked Dr Garnsworthy.

When cows were kept within the optimum range of diet specification and body condition, the effect of nutrition on fertility could be minimised, he concluded.

FEEDING AND FERTILITY

&#8226 Interaction identified.

&#8226 Nutrition rarely at fault.

&#8226 Effect can be minimised.