Environmental factors, management, and genetics all play a part in determining a stallion’s fertility. Bhanu P. Chowdhary, BVSc, AH, MVSc, PhD, associate professor in animal genomics at Texas A&M University’s College of Veterinary Medicine, has turned his attention to the role of genetics, specifically on the Y chromosome, in finding causes of stallion infertility. He presented information on his current research on this topic, and his long-term goals to be able to genetically diagnose stallions with Y chromosome-related fertility problems, at a recent University of Kentucky Gluck Equine Research Center lecture for equine researchers, students, and practitioners.

According to Chowdhary, the Y chromosome was largely ignored, compared to other chromosomes, because it was thought to only determine sex. It was often called a “genetic wasteland, junkyard, a barren chromosome, an ’empty dance partner’ for X, a genetic couch potato, an adolescent tearaway, and a degenerate,” he said.

In June 2003, after scientists deciphered the role of genes on the human Y chromosome, Chowdhary said the chromosome was “suddenly considered to be a ‘goldmine,’ ‘crystal palace,’ and ‘hall of mirrors,’ ” because of its bizarre organization and potential role in causing  male infertility, sex reversal, gonadal dysgenesis (in which an infected individual looks like female but has male chromosome composition, specifically a defective Y chromosome), aging, and cancer. Y chromosome DNA can also be useful for forensic analysis and paternity testing. “Finally the Y chromosome got some stardom, and wasn’t just referred to as the sex-determining chromosome,” he said.

Six percent of human males are completely infertile, and 25-30% of those men are infertile because of causes on the Y chromosome–usually rearrangements or deletions. “We cannot overlook this major factor as non-existent in horses,” said Chowdhary, “I suspect something similar is happening in them, too.” After looking into available research, Chowdhary saw that very little is known about the genetic causes associated with reduced fertility or infertility in stallions. While he’s examining these causes on other chromosomes, he’s specifically targeting the horse Y chromosome and the genetic factors it harbors for stallion fertility