A method to obtain pregnancies in mares using minimal sperm numbers

摘要

Generally, mares are inseminated with 500 million progressively motile (PMS) fresh sperm, approximately 1 billion total sperm, that have been cooled, and 800 million to 1 billion spermatozoa that have been frozen and thawed. This limits the number of mares that can be bred. Sperm placed into the uterine body are at the uterotubal junction or within the oviducts by 4 hr postinsemination. The majority of mares experience postbreeding endometritis, which generally is resolved by 24 hr postbreeding. Some older mares have a more severe postbreeding endometritis and accumulate fluid. This is particularly true of mares bred with frozen/thawed spermatozoa. One possible means of diminishing this post-breeding endometritis would be to deposit the sperm directly on the uterotubal papilla at the anterior tip of the uterine horn, ipsilateral to the ovary containing the dominant preovulatory follicle. Other potential advantages of insemination at the level of the uterotubal junction would include frozen sementhat is of limited supply, semen from a subfertile stallion with limited sperm numbers, stallions that are heavily "booked," and insemination of sexed semen. Due to the current relatively slow rates of sorting spermatozoa into X and Y chromosome-bearingsperm, a low number of spermatozoa must be used. Deep uterine insemination is a proven technique in cattle that allows the sperm number to be decreased without dramatically affecting fertility. This report summarizes several studies on pregnancy rates of mares inseminated with low numbers of either non-sexed or sexed spermatozoa by deep uterine insemination using a flexible catheter or by video endoscopic insemination.