Value of testicular and sperm profiles in optimizing reproductive success: lessons learned from selective breeding programs of domestic and laboratory animals.

The economic potential of the biotechnology of artificial insemination for genetic improvement and disease control was recognized in the United States 50 years ago. To fully exploit this technology in dairy cattle, researchers worked closely with industry to study testicular function, best methods for harvesting and evaluating semen, techniques for preserving and inseminating sperm and finally, methods for mass recording of fertility information. Methods of testicular and semen evaluation have been developed which are highly correlated with other reproductive characteristics, including fertility. This has resulted in an unprecedented opportunity to study experimentally imposed conditions and naturally occurring environmental conditions upon reproductive efficiency in the male. The selection and testing of sires has resulted practically in the elimination of genes which produce lethal or severely depressed performance. The use of one male for the controlled insemination of many females also has facilitated studies on reproductive problems in the female. While less selective breeding programs have been conducted with the rabbit relative to reproductive function, the rabbit has been used extensively as a model for large domestic animals and humans. The rabbit is the smallest laboratory animal which can be trained easily to ejaculate into an artificial vagina and use the semen for insemination. This permits longitudinal and correlative studies to be performed relating testis function and epididymal transport to sperm output, semen quality and fertility. Spermatogenesis of both bulls and rabbits is sensitive to toxicants. The effects can be monitored by testicular biopsy and cytological evaluation of the testis, by semen collection and semen evaluation, and by in vitro and in vivo fertility testing. Gross effects on the testis are detectable in the live animal by measuring testis size and by ultrasound profiles.