1 October 1999

Mind the lactation gap

HIGH yielding dairy cows suffer a shortage of energy for the first 14 weeks of lactation and 0.5 to 0.75kg of body tissue a day.

However, for cows yielding 50 litres this loss in body tissue is not reflected in actual body weight loss, David Beever of CEDAR, Reading, told EDFEvisitors.

"Body weight loss ceases after five weeks, when cows start to gain a small amount." But this doesnt reflect the actual tissue loss; studies show cows continue to eat less than required and break down fat, even on the best possible ration.

Cows averaging 49 litres in the first year of this MDC-funded study ate 25kg dry matter of a maize silage ration, compared with 22kg for cows producing 37kg.

The reason body weight can increase is that the cow is eating and drinking 170kg a day. "Thats equivalent to her own body weight every four days." Body condition score loss follows tissue loss more accurately, he added.

Body tissue loss over the 14 week energy gap period is equivalent to the energy required to produce 400 to 500 litres of milk, explained Prof Beever.

"The challenge now is to reduce the energy gap by manipulating and flattening the lactation curve.

"We cant expect to stop cows losing tissue totally; but if it only lasts eight or nine weeks, and we can identify the period by condition scoring, we can serve cows after that gap."

This may help overcome fertility problems in high yielding and high merit cows, which are also being studied in another MDC-funded project.

The studys second and third year will look at feeding these cows to reduce the energy gap economically, and maintain milk quality.

They will also substitute grass silage for maize silage to see how much can be fed without reducing performance. But he believes feeding grass silage as the only forage will be insufficient to support these high yielding cows adequately.

MIND THE GAP

* Can last 14 weeks.

* May contribute to poor fertility.

* Check by condition scoring.

ENERGY GAP

&#8226 Can last 14 weeks.

&#8226 May contribute to poor fertility.

&#8226 Check by condition scoring.