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Stallion Health: Dual-Hemisphere BreedingBy Kentucky Equine Research Staff · May 17, 2017

Stallions work hard to fulfill their breeding duties each year, with some popular Thoroughbreds covering almost 200 mares in a single season. When those stallions become so-called “shuttle stallions,” does their success rate remain constant, or are they overworked?

In this context, the term “shuttle stallion” refers to a stud that breeds in one hemisphere for a season before being shipped to the opposite hemisphere for the next breeding season (e.g., Ireland and Australia). Effectively, this strategy doubles the number of foals sired by a particular stallion and potentially increases genetic diversity within the breed in each location.  

Although previous research suggests that dual-hemisphere (DH) breeding has no negative impact on stallion fertility, one group of veterinary researchers from Texas A&M University decided to look into the matter more comprehensively. In their latest study*, the researchers analyzed various outcome parameters such as seasonal pregnancy rates and first-cycle pregnancy rates for different groups of stallions based on whether they were single or dual-hemisphere breeders.

The researchers concluded that DH breeding did not have a detrimental effect on fertility. Specifically, they found:

  • Fertility in the Southern Hemisphere was higher than the Northern Hemisphere; however, there were more maiden and fewer barren mares in the south;
  • Stallion fertility did not change when DH breeding was interrupted by single-hemisphere breeding; and
  • Stallion fertility was not affected by consecutive DH breeding seasons. In this study, some stallions participated in up to 10 DH breeding seasons.

“Other ways to the optimize breeding success of any stallion include ensuring appropriate body condition without becoming especially underweight or overweight; providing a balanced diet that includes a full complement of vitamins and minerals; and maximizing joint health and semen quality,” advised Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research (KER).

KER offers nutritional consultations and recommends supplementing stallions with EO•3, a marine-derived oil rich in omega-3 fatty acids, including DHA and EPA. Omega-3 fatty acids benefit reproductive parameters in both stallions and broodmares, and support hard-working joints.

*Walbornn, S.R., C.C. Love, T.L. Blanchard, et al. 2017. The effect of dual-hemisphere breeding on stallion fertility. Theriogenology. 94:8-14.