Colt or Filly? Breeders Soon Might be Able to Choose

Researchers are studying whether magnetic nanoparticles could effectively separate “X” and “Y” stallion spermatozoa.
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By Maria Paz Zuñiga, DVM, WEVA Board Member

Scientists and breeders have been pursuing sex preselection before conception for years. In dairy and meat cattle industries there are financial benefits to producing one calf sex or the other. However, choosing a sex for horses tends to have more subjective reasons or be related to athletic performance.

Until now, the only replicable and efficient way to separate the sperm that contains the X chromosome from those that contain the Y chromosome from a semen sample is by sorting the cells with a high-flow cytometer. However, it has only been used commercially (not in day-to-day equine practice) and on a large scale in the dairy cattle industry. The number of spermatozoa that can be effectively selected per hour in the flow cytometer has been a limitation for its mass application, especially for species that require a high number of sperm to inseminate a female, as is the case with horses.

The main factors that affect gestation rates with flow-cytometer-sexed semen are the low numbers of spermatozoa available for insemination; the sperm damage by high pressure speed flow, DNA stain, and ultraviolet light exposure; and the cryopreservation process of these sex-sorted spermatozoa

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