Goats and sheep – Strutting their stuff

The ‘male effect’ is a natural and ethical way to better reproduction in goats and sheep, says Roelof Bezuidenhout.

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Using vasectomised (teaser) rams to bring ewes into oestrus, boost their ovulation rate and shorten the breeding season, is known as the ‘male effect’. The presence, behaviour and smell of rams increase the production of a hormone that stimulates ovulation in ewes, explains Dr Johan van Rooyen of the Grootfontein Agricultural Development Institute.

This method is increasingly preferred over other practices involving vaginal devices and pregnant mare serum gonadotropins (PMSG). A gonadotropin is a hormone that stimulates the function of the ovaries and testes. Many consumers now reject the use of hormones originating outside an animal’s body, notes Van Rooyen. In addition, PMSG can cause ewes to carry four or more lambs, resulting in ewe mortalities and reduced viability of lambs.

“Attention has switched to clean, green and ethical strategies that use natural alternatives to improve reproductive rates, while not compromising the acceptability of livestock products,” he says. The current emphasis is on using teasers in combination with lupins, or another suitable feed, to improve the ovulation rate in ewes and semen quality in rams.

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Better management, nutrition and genetic selection to improve offspring survival are also employed.

Common misconceptions

Research suggests that there are certain misconceptions about the male effect, explains Van Rooyen. For example, it is traditionally accepted that females must be completely isolated from males, and should not even be downwind from them. But this is unnecessary.

Furthermore, although some studies indicate a response after only a few hours of exposure, the overwhelming evidence is in favour of continuous exposure for 17 days rather than short-term exposure every 17 days, he adds. The perception that the male effect is purely the result of smell has also been proven incorrect. Ewes also respond to the behaviour and ‘novelty’ of the ram.

“In fact, ewes recognise novel rams and respond to them even if they’re running with other rams,” says Van Rooyen. He adds that adult males are more efficient at creating the male effect because their odour is stronger. He therefore urges flock managers to ensure a constant stream of new teaser rams to avoid having to replace all teasers at the same time with young rams.

Testosterone-treated wethers can also be used, along with vasectomised males, and can help to break up harem groups, ensuring higher levels of ewes’ exposure to rams. One study showed that Ronderib Afrikaner teaser rams led to better ovulation rates in Merino ewes than Merino rams did. The ovulation rates were 28,9% and 14,4% higher in the spring and autumn, respectively.

They exhibited some behaviour in common with goats, such as soiling the belly with urine, leading to the characteristic ‘goat ram smell’ during the breeding season. Untreated rams introduced for short periods (two to four days) pre-breeding have been found to be less effective in eliciting the male effect than vasectomised rams introduced for 17 days before breeding.

How the male effect works
In sheep, introducing a ‘novel’ ram results in ovulation in the ewe within 30 to 72 hours, and again on the sixth day. But teaser rams must be introduced 15 days to 17 days before mating, as shorter periods result in fewer ewes coming into oestrus.

During the non-breeding season, ewes return to anoestrus after one or two ovulations. In one trial, when Merino ewes were introduced to teaser rams, half of them failed to ovulate during the menstrual cycle. This is why it is advisable to introduce teasers approximately seven days before the breeding season in spring, gradually increasing the period to 17 days in autumn.

Roelof Bezuidenhout is a fourth-generation Karoo small-stock farmer.