**6.3 The Whitten effect**

*Animal Reproduction in Veterinary Medicine*

the boar pheromone have been described.

the effect.

**6.1 The Bruce effect**

to a lower farrowing rate.

Bruce effect.

described.

determined.

**6.2 The Vandenbergh effect**

fighting [39, 51]. None of these releasing pheromone molecule(s), other than

What can we learn from other mammalian sexual pheromones? Given that the pig has so many functional receptors, it is likely that if a type of pheromone was described in another mammal that the pig would have a pheromone with a similar effect. Here we summarize the classic reproductive pheromones. Note that each early reproductive pheromone was named after the scientist who first reported

Hilda Bruce described what has been called the Bruce effect in 1959 [52]—before

the concept of pheromone was established. She showed that when a pregnant mouse was exposed to an adult male, preferably a dominant male, that the pregnant mouse lost her pregnancy. The Bruce effect has been replicated by many investigators and what we know is that each male has a specific major histocompability complex (MHC) class 1 protein that is secreted in its urine. The father of the mouse litter has a given MHC protein. If a new male enters the cage with a different MHC protein, the female is likely to lose her pregnancy (not 100% of the time, but at a significant rate). The male MHC protein binds the VNO in the female mice. It makes one wonder if heat checking with a boar during pregnancy might contribute

The Bruce effect has not been clearly documented in the pig. Assuming the Bruce effect is found in pigs, one would change the management of the sow herd. On most farms, pregnant sows experience a live, often dominant, boar walking the aisle to see if any bred sows are now in heat (meaning their pregnancy has failed). That live boar would not have the same MHC as the father of the litter because they are commonly bred by artificial insemination. We know that a small (5–10%) percentage of sows lose their pregnancy from breeding until farrowing. Part of this effect could be due to the Bruce effect. To manage this situation, pregnant sows should never experience a live boar that is not the father of her litter or perhaps is not the boar present during breeding. Keeping in mind that the Bruce effect is mediated by MHC proteins and not the boar pheromone, one can use the boar pheromone to check for return to estrus in pregnant sows without inducing the

John Vandenbergh first described this pheromone in a paper published in 1975 [53]. He showed that female mice have an accelerated onset of puberty when exposed to an adult male mouse or urine from an adult male mouse. The molecule was thought to be a protein, but the actual molecule had not been

Pigs clearly show the Vandenberg effect. Gilts will have a delayed onset of puberty if they do not experience an adult boar. With boar exposure, the onset of puberty is accelerated in gilts [54]. The pheromone molecule(s) that are responsible have not been described. One might predict that the boar pheromone that stimulates sow reproductive behavior and performance [5], is the same pheromone that stimulates the accelerated onset of puberty in gilts. However, if these boar pheromone molecules are responsible for the Vandenberg effect in gilts, then the dose and number of applications required to cause the Effect have not yet been

**50**

Whitten described the Whitten Effect in a number of papers from 1956, 1957 and 1966 and 1968 [55–58]. The Whitten Effect states that in a group of postpubertal females, the presence of either other cycling adult males will cause the females to synchronize their estrus (or menstrual) cycles. Likewise, adult females tend to synchronize their cycles over time when they are housed together. The Whitten Effect has no valuable application in modern pork production at this time that we can think of; however, production systems change over time and there could be an application in the future. The Whitten Effect takes weeks or months to have its effect. Therefore, we do believe that when gilts approaching puberty are exposed to a boar, that the number or percentage that come into estrus is not evenly distributed over the 21-day cycle, so this may be happening. Boar exposure may partially synchronize a group of gilts first estrus.
