Nutrition the key to deer gestation

A New Zealand scientist has found red deer have shorter gestations when they have access to good-quality feed.

The quality and quantity of the feed can influence the gestation period of pregnant hinds by up to an amazing 28 days, says scientist Dr Geoff Asher.

"Nutrition has an unexpected impact on deer reproduction," he said.

While nutrition during pregnancy was known to affect the foetal growth, birth weight and lactation of all species, the large spread in gestation length depending on feed intake found in red deer was unique.

They normally have an eight-month gestation.

The discovery would be extremely useful for farmers managing the nutrition and reproduction of their herds in the battle to boost production of fawns in October and November.

Most red deer calve in December, too late to take best advantage of the spring flush of growth.

Ideally, farmers want deer to produce fawns in mid-September, so that they can be fattened for Christmas dinners in Europe.

Because most New Zealand farm-raised venison is sold in Northern Hemisphere markets, producing earlier fawns can significantly boost farmers' export earnings.

Conventional hormonal preparations, used to stimulate out-of-season breeding in other animals, such as sheep, have been found to be relatively ineffective in deer.

Melatonin, successfully used in sheep, advanced the breeding season of deer by only 20 days, which was not enough to justify the effort or cost.

Three years ago, another line of research led to red deer calves being born four months earlier than usual at Lincoln University after scientists cut the thyroid glands of hinds, which affected the breeding season.

Without the gland, deer could mate at any time.

But because performing surgery on farmed deer was regarded as unethical, the Lincoln researchers began looking at blocking the actions of the thyroid hormone without the need for surgery.

Dr Asher, who works at AgResearch's Invermay centre at Mosgiel, said his own research had shown considerable differences of opinion among deer farmers on appropriate feeding of hinds during the last stage of pregnancy - ranging from ad-lib feeding to highly restricted feeding.

Under New Zealand pastoral farming practices, late pregnancy in red deer hinds coincides with the spring pasture flush.

Some farmers had restricted hind feeding on the grounds that overfeeding on this high-quality feed could lead to excessive fatness and overdevelopment of the foetus, which caused difficult births.

Other farmers had argued that luxury nutrition in late pregnancy improved birthweights and promoted lactation.

Dr Asher found red deer could adjust gestation length to compensate for differing levels of foetus growth.

"New Zealand farmers may be compromising calving dates within their herds by applying extreme nutritional management practices," he said.

This could affect their ability to meet the industry's push for early calving dates.

- NZPA