26 October 2001

Lack of dietary energy main cause of infertility

By Richard Allison

INSUFFICIENT dietary energy is the main cause of nutrition-related dairy cow infertility, not feeding excess protein as widely believed, according to experts.

This was the main finding from an MDC funded review, prompted by the continuing fertility decline.

There is a common misconception that high levels of dietary protein result in a high milk urea content which leads to poor fertility, says ADAS Bridgets researcher Helen Biggadike.

"There are herds with high milk urea which still have good fertility. Insufficient dietary energy can also cause elevated milk urea levels, but excess protein is often wrongly blamed."

Too much protein in the diet makes the adverse effect of negative energy balance on fertility worse. Based on experience, Promar nutritionist Diana Allen has found that even cows yielding more than 8000 litres only need a maximum protein level of 18.5%.

Negative energy balance usually occurs during weeks one to 12 of lactation and is seen as body condition loss. "Ideally, cows should have a flatter lactation curve, more like heifers, to spread energy requirements and minimise body losses in early lactation."

Body condition loss during early lactation has been shown to increase calving interval by between nine and 19 days, equivalent to £21-48/cow in additional costs. "The average UK calving interval is about 400 days with a barren culling rate of 18%, which is appalling and getting worse," adds Mrs Allen.

However, it is still economically worthwhile to inseminate an average yielding cow up to 266 days post-calving and high yielding cows up to 290 days, says Miss Biggadike. "After this point, the cost of culling is lower than the cost of extended calving interval."

To combat infertility due to negative energy balance, body condition must be monitored routinely and data used to formulate rations. Mrs Allen adds that out of 20 workshops she organised, only one producer scored cows routinely and used this information.

"The problem is producers see cows every day and believe they know what body reserves they have. But they cannot pick out gradual changes in body condition until it is too late."

To save time, monitor about six cows in each calving month. Where body condition loss exceeds 0.5 in the first month of lactation, adjust the ration to increase energy intake. Duration of condition loss should also be restricted to less than 42 days, she warns.

Accepting a one point loss in body condition score will save the equivalent of about £12 of wheat. But the cost of reduced reproductive performance is about £20-30 for each half point loss in body condition, says Miss Biggadike.

High yielding cows can also lose internal body reserves during late gestation, while appearing to maintain condition. This is becoming more widespread due to the practice of feeding straw to avoid dry cows becoming over fat, stresses Mrs Allen. &#42

There are herds with high milk urea levels which still have good fertility, says Helen Biggadike (inset).

FEEDINGFORFERTILITY

&#8226 Ensure adequate energy.

&#8226 Monitor body condition.

&#8226 Maximise dry matter intake.