20 Trials and Tribulations of Countering Insufficient Sperm Quantity with Sperm Quality, Fertility, Synchrony and Deeper Site of Insemination

Abstract

Abstract Superior tools and techniques for boar semen evaluation, semen preservation and artificial insemination (AI) have helped build industry confidence and competence to reduce sperm per female inseminated without compromising reproductive results. Over the last 30 years, the average number of sperm per AI dose has decreased from about 5 to 2 billion in the US and doses containing 1.5 billion sperm have become common in some other countries. While even more genetic lag can be eliminated by further reduction of sperm dose, the level at which fecundity and fertility loss occurs is not a constant and likely varies between different farms and production systems. In general, uterine delivered sperm doses near or lower than 1 billion tend to reduce litter size and further sperm dose reduction eventually reduces pregnancy rate. Deeper catheter deposition of semen, beyond the uterine body, does not seem to effectively compensate for a limiting quantity of sperm. The exception is that surgical injection of sperm into the oviducts requires much less sperm than intrauterine insemination. Reduction of the AI-to-ovulation interval, from 24 to 8 h for example, does not seem to ameliorate the negative effects of a limiting number of sperm when sperm quality is high. The exception may be that a shorter AI-to-ovulation interval can increase reproductive results when both sperm quantity and quality are limiting. Examples include low boar fertility, advanced semen age, or sperm quality compromised by cryopreservation or sex-sorting. A better understating of boar fertility, the interaction of sub-populations of sperm with the oviductal reservoir and their participation in fertilization is likely requisite to continued reduction of the number of sperm required per female. Technologies that predict or regulate sperm quality, fertility and ovulation could prove useful in the quest to use sperm more efficiently and add value to swine AI.