**2. Sexual behavior in the domestic pig: early studies and preferred terminology**

While pig farmers have observed sexual behavior for millennia, the earliest scientific description of sow sexual behavior in the scientific literature was in 1941 by Altmann [3]. Altmann was a psychologist at the University of Chicago when animal

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**Figure 2.**

*Drawings of sow-boar sexual behaviors from Signoret [4].*

*Understanding Sow Sexual Behavior and the Application of the Boar Pheromone to Stimulate…*

behavior was developing in the USA. Altmann studied female pig sexual behavior because she used pigs in her conditioning studies, and she wanted to be sure if sows were or were not in heat when she trained them on an operant task. In 1941, she reported several aspects of sow sexual behavior that we know to be true. She said there was a 18–23 day cycle among adult females. She indicated that domestic sows (unlike wild boar) bred year-round, although they often had a "silent heat" in warm weather. She found external signs of estrus to be not reliable indicators of estrus; these included, vaginal mucous, swelling of the vulva and rectal temperature changes. We recently confirmed her observations with quantification of anatomical changes (see below). She indicated behavior and activity were the best methods to

The next scientist to publish studies in pig sexual behavior was Jean Pierre Signoret from France. His research on sow sexual behavior in the 1960s and early 1970s were summarized in a chapter Signoret co-wrote in Hafez's 1964/1968/1975 editions of the book "The Behaviour of Domestic animals" [4]. The picture of sowboar sexual behavior in that chapter has been widely used to describe pig's sexual behavior. In that picture, he lists sequences of boar-sow behaviors that are shown in **Figure 2**. The sequence of sexual behaviors between a sow and boar include mutual head sniffing, and then the boar sniffs the sow's rear, he then pushes and may lift the sow from the side, then he sniffs and licks and pushes on the sow's rear. These olfactory and tactile behaviors are accompanied by grunting by the boar and, if the sow is in estrus, she will be silence or she will make soft rhythmic grunts in response (she will squeal if she is not in estrus as a form of objecting to the boar behavior). After touching, smelling and licking her rear, he will mount her and if she is fully in estrus and showing "standing reflex or locked up" behavior, he will copulate with her.

determine heat, but a combination of methods increased accuracy.

*DOI: http://dx.doi.org/10.5772/intechopen.90774*
