Foal Sex Selection

Sex selection of foals prior to conception is highly desirable for horse breeders. Currently, sperm can be sorted by their X and Y chromosomes, improving odds of sex selection through artificial insemination. Flow cytometry measures DNA in cells and can sort sperm, but it's time-consuming and damages sperm, leading to great losses during the procedure. Freezing sperm destroys many cells, leaving fewer for insemination. Techniques for placing sperm closer to the egg as it is ovulated are now being used to improve pregnancy rates with low numbers of sperm. A recent study from the Colorado State University made use of one of these techniques, called hysteroscopic insemination, to examine the effects of sorting and freezing of sperm on stallion fertility and pregnancy rate after insemination.

Semen was collected from seven stallions. Forty-one mares in four groups received fresh/non-sorted, fresh/sorted, frozen/non-sorted, or frozen/ sorted sperm. Mares were inseminated with 5 million sperm (compared to the usual dose of 500 million sperm) placed near the opening of one oviduct. Pregnancy rate was not statistically different between sorted and non-sorted sperm among either fresh or frozen semen paired groups, ranging from 40% using fresh/non-sorted sperm to 13.3% for frozen/sorted sperm. However, due to the small number of mares in the study, the statistical results are questionable.

Still, two of 15 mares inseminated with frozen/sorted sperm became pregnant with the chosen sex (one male, one female). Also, a 40% pregnancy rate was achieved using only 5 million fresh sperm, which means that low sperm number inseminations can indeed be successful, and sex-selection research is likely to move forward.

Lindsey, A.C.; Schenk, J.L.; Graham, J.K., et al. Equine Veterinary Journal, 34(2):121-127, 2002.

About the Author

Susan Piscopo, DVM, PhD

Susan Piscopo, DVM, PhD, is a free-lance writer in the biomedical sciences. She practiced veterinary medicine in North Carolina before accepting a fellowship to pursue a PhD in physiology at North Carolina State University. She lives in northern New Jersey with her husband and two sons.

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