Sexual behaviour has implications for reproductive success

That come-hither look between males and females is not witchcraft.

Expressions of sexual behaviour in livestock help identify mates and optimize fertilization, said Brenda Alexander, a professor of reproductive biology of the University of Wyoming.

“In the end reproductive behav-iour matters because the vast majority of births are occurring because of natural service,” she said in March 25 webinar.

In the United States, about 10 percent of the cow population is artificially inseminated or impregnated using some other form of reproductive technology. The other 90 percent of cattle births are from natural service. Among small ruminants most are conceived naturally so most births are natural.

Alexander’s research focuses on the reproductive behaviour of small ruminants but similar sexual situations occur among other species.

Behaviour of the male matters and he is expected to mate with many different females, she said. The male is responsible for genetic progress and among those with less interest in mating, there could be fewer offspring.

Her studies of rams found as many as 24 percent lack sexual interest.

It all starts in the brain.

Rams with low sexual performance have deficits in the brain-reward pathway that may account for their lack of interest. The ewe can influence interest but cannot compensate if the male is not interested.

Rams identify ewes in heat by smell and high-performing males mount quickly.

Poor performing rams generally have adequate levels of testosterone but are less active and apt to select one ewe and mount her repeatedly rather than move on to a new one.

Active rams lack discrimination once they are turned out with the ewes.

“This is a trait we rely on in the agriculture world. We really expect them not to have a selective preference for a ewe. We want them to mount many ewes,” she said.

Female goats can discriminate among males and can select those with the most testosterone as opposed to their phenotypic attributes.

The female also emits strong ram seeking behaviour and there is an increase in the amount of estrogen when they look for the male.

She will position herself and look at the ram over her shoulder. This behaviour is less common when the female is exposed to a low-performing ram.

Selecting a high-performing ram is not practical because it takes time.

“In a farm situation, it is hard to identify these low-performing males. Producers get around this by increasing the number of rams they put with their females,” Alexander said.

She could not say how heritable this trait is. In other species like chickens and cattle there is a heritability component. It is also known that female offspring from high-performing rams cycled at an earlier age.

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