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Low dose insemination of mares with non-sorted versus sex-sorted sperm
Mares are generally inseminated with 500 million progressively motile fresh sperm and approximately 1 billion total sperms that have been cooled or frozen. If the low-dose insemination technique is effective, much more mares can profit from such a semen portion. A very informative study!

Development of techniques for low dose insemination would allow one to increase the number of mares that could be bred, utilize stallions with poor semen quality, extend the use of frozen semen, breed mares with sexed semen and perhaps reduce the incidence of post-breeding endometritis.

Three low dose insemination techniques that have been reported include: surgical oviductal insemination, deep uterine insemination and hysteroscopic insemination.

Insemination techniques: McCue et al. [J. Reprod. Fert. 56 (Suppl.) (2000) 499] reported a 21% pregnancy rate for mares inseminated with 50,000 sperms into the fimbria of the oviduct.Two methods have been reported for deep uterine insemination.

In the study of Buchanan et al. [Theriogenology 53 (2000) 1333], a flexible catheter was inserted into the uterine horn ipsilateral to the corpus luteum.

The position of the catheter was verified by ultrasound. Insemination of 25 million or 5 million spermatozoa resulted in pregnancy rates of 53 and 35%, respectively.

Rigby et al. [Proceedings of 3rd International Symposium on Stallion Reproduction (2001) 49] reported a pregnancy rate of 50% with deep uterine insemination. In their experiment, the flexible catheter was guided into position by rectal manipulation.

More studies have reported the results of using hysteroscopic insemination. With this technique, a low number of spermatozoa are placed into or on the uterotubal junction.

Manning et al. [Proc. Ann. Mtg. Soc. Theriogenol. (1998) 84] reported a 22% pregnancy rate when 1 million spermatozoa were inserted into the oviduct via the uterotubal junction.
Vazquez et al. [Proc. Ann. Mtg. Soc. Theriogenol. (1998) 82] reported a 33% pregnancy rate when 3.8 million spermatozoa were placed on the uterotubal junction.
Recently, Morris et al. [J. Reprod. Fert. 188 (2000) 95] utilized the hysteroscopic insemination technique to deposit various numbers of spermatozoa on the uterotubal junction. They reported pregnancy rates of 29, 64, 75 and 60% when 0.5, 1, 5 and 10 million spermatozoa, respectively, were placed on the uterotubal junction.

Insemination of sex-sorted spermatozoa: One of the major reasons for low dose insemination is insemination of X- or Y-chromosome-bearing sperm. Through the use of flow cytometry, spermatozoa can be accurately separated into X- or Y-bearing chromosomes.

Unfortunately, only 15 million sperms can be sorted per hour. At that rate, it would take several days to sort an insemination dose containing 800 million to 1 billion spermatozoa.

Thus, low dose insemination is essential for utilization of sexed sperm.

Lindsey [Hysteroscopic insemination with low numbers of fresh and cryopreserved flow-sorted stallion spermatozoa, M.S. Thesis, Colorado State University, Fort Collins, CO, USA, 2000] utilized either deep uterine insemination or hysteroscopic insemination to compare pregnancy rates of mares inseminated with sorted, fresh stallion sperm to those inseminated with non-sorted, fresh stallion sperm.

Hysteroscopic insemination resulted in more pregnancies than ultrasound-guided deep uterine insemination.

Pregnancy rate was similar for mares bred with either non-sorted or sex-sorted spermatozoa.In a subsequent study, Lindsey et al. [Proceedings of 5th International Symposium on Equine Embryo Transfer (2000) 13] determined if insemination of flow-sorted spermatozoa adversely affected pregnancy rates and whether freezing sex-sorted spermatozoa would result in pregnancies.

Mares were assigned to one of four groups:
group 1 was inseminated with 5 million non-sorted sperms using hysteroscopic insemination;
group 2 was inseminated with 5 million sex-sorted sperms using hysteroscopic insemination;
group 3 was inseminated with non-sorted, frozen-thawed sperm;
and group 4 was inseminated with sex-sorted frozen sperm.

Pregnancy rates were similar for mares inseminated with non-sorted fresh sperm, sex-sorted fresh sperm and non-sorted frozen sperm (40, 37.5 and 37.5%, respectively).

Pregnancy rates were reduced dramatically for those inseminated with sex-sorted, frozen-thawed sperm (2 out of 15, 13%).

These studies demonstrated that hysteroscopic insemination is a practical and useful technique for obtaining pregnancies with low numbers of fresh spermatozoa or low numbers of frozen-thawed spermatozoa.

Further studies are needed to determine if this technique can be used to obtain pregnancies from stallions with poor semen quality. In addition, further studies are needed to develop techniques of freezing sex-sorted spermatozoa.

Source: Lindsey AC, Bruemmer JE, Squires EL. (2001): Low dose insemination of mares using non-sorted and sex-sorted sperm. In: Anim Reprod Sci. 2001 Dec 3;68(3-4):279-89.

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