Low dose insemination in the sow--a review.

Artificial insemination (AI) in pigs has been established for about four decades but ejaculates are still used insufficiently. Higher demand of semen for AI and new techniques that involve low sperm concentration require the optimization of insemination protocols. Based on the knowledge of the physiology of sperm transportation and events in the female genital tract prior to fertilization, new strategies are under development to minimize sperm losses. One goal is to deposit the semen into the uterine horn rather than into the proximal cervix. It was shown that the minimal number of spermatozoa necessary for surgical AI at the utero-tubal junction (UTJ) were at least 1 x 10(6) diluted in 0.5 ml of a special extender. Artificial insemination into the distal part of the uterine horn required about 1 x 10(7) million sperm in 20 ml of extender. Meanwhile, first insemination devices for non-surgical intra-uterine AI are commercially available. Using similar sperm concentrations as for surgical AI, non-surgical uterine insemination did not differ significantly from control inseminations in terms of pregnancy rate and litter size. With respect to the fertilizing capacities of their ejaculates, boars have to be selected more strictly for sperm quality parameters as most of the compensatory effects of sperm cells disappear in maximally extended semen samples.