Social and sexual factors affecting reproduction of the domestic boar

This thesis describes the results of work in three general areas; (i) the influence 0f the social environment during rearing and after puberty on the sexual behaviour of the boar, (ii) the role of the courting behaviour of the boar in his reproductive performance, and (iii) the influence of sexual stimulation on the spermatozoan output of the boar. The major portion of the work relates to the importance of the social environment. Boars reared from three weeks of age in the absence of visual and physical contact with pigs had markedly lower copulatory performance and level of courting activity compared with those reared from three weeks in either an all-male or mixed-sex group. Lack of physical contact with pigs during rearing was responsible for approximately 70% of this depression in copulatory performance. The copulatory performance of boars reared from 12 weeks of age in the absence of visual and physical contact with pigs was considerably less than that of boars reared in an all-male group, but the difference was not significant. Boars reared from three or 12 weeks- of age individually in adjacent wire-mesh pens had similar copulatory performance to that of group-reared boars. However, an apparently important feature of courting behaviour, 'nosing activity', was significantly reduced for those boars reared from three weeks individually in adjacent wire-mesh pens. These data were interpreted as evidence of the importance of social contact, particularly physical contact with boars or gilts, during rearing on the level of sexual behaviour of the boar. In addition to the social environment during rearing, the social environment after puberty was demonstrated to have a dramatic influence on the level of sexual behaviour of the boar. Isolation of post-pubertal boars from female pigs for six weeks significantly reduced their copulatory performance and level of courting activity. The stimuli received from the presence of sexually receptive or sexually non-receptive female pigs were equally capable of maintaining the level of sexual behaviour of the boar. Two experiments conducted at a commercial piggery revealed the importance of the courting behaviour of the boar on reproductive performance. A significant positive correlation was found between the observed level of nosing activity during courting and the conception rate record of the boar. The proposal that the nosing activity of the boar may stimulate one or more physiological mechanisms leading to fertilisation in the sow is supported by the results of the second experiment. Brief courting of sows by a boar prior to artificial insemination significantly increased the farrowing rate and litter size of group-housed sows. Finally, sexual stimulation of boars prior to semen collection significantly increased the number of spermatozoa . in the sperm-rich fraction of the ejaculate. The technique of sexual stimulation of the boar involved either allowing the boar a false mount and then briefly restraining him or allowing the boar to observe a semen collection. The former technique failed to maintain a significant increase in the yield of spermatozoa from the sperm-rich fraction over a six-week collection period. Prostaglandin F2a, which may be involved in the mechanism by which sexual stimulation increases the number of spermatozoa in the short term, was also studied. Administration of 20 mg of PGF2a 30 minutes before collection significantly increased the number of spermatozoa in the sperm-rich fraction of the ejaculate. The experiments of this thesis demonstrate that sexual and social factors have a major influence on the reproduction of the domestic boar