Sexual behaviour, sperm production and fertility in boars under intensive ejaculation rhythm

Abstract

The aim of the study was : 1 / to measure the influence of high ejaculation rhythm on sperm production, 2 / to compare semen collection and natural mating, and 3 / to test the fertility of gilts mated by boars under various ejaculation frequencies. 15 Yorkshire of Landrace boars of an average age of 10 months at the onset of the experiment ejaculated either for semen collection or for natural mating of œstrous gilts at a rhythm of 1, 2, 3, or 4 times a day for 5 days after 2 weeks of sexual rest. The gilts were slaughtered either immediately after mating to measure the volume of the ejaculate and the number of spermatozoa, or 35 days later to test fertility. All the boars ejaculated once a day, but only 91.6, 58.3 and 41.5 %, at rhythms of 2, 3 and 4 times a day respectively. Increasing the ejaculation frequency from 1 to 2 and 4 decreased the number of spermatozoa per ejaculate from 15 billion to an average of less than 10 and 5 billion, respectively. The volume and the number of sperm was the same with both natural mating and semen collection. However, an average of 40 % of the ejaculate flew black from the female genital tract during natural mating. The reduction of the number of sperm ejaculated, and the sperm loss resulted in a reduced pregnancy rate at high ejaculation frequency in natural mating : respectively 91.6 % and 58.3 % after one and four ejaculates per day. Sperm production, rather than sexual capacity, appear to be the limit for the use of the sire at high mating frequency resulting for instance from mating of sows for the purpose of batch farrowing.