The effect of dual-hemisphere breeding on stallion fertility
Authors: Walbornn S.R., Love C.C., Blanchard T.L., Brinsko S.P., Varner D.D.
Journal: Theriogenology
Summary
# Editorial Summary: Dual-Hemisphere Breeding and Stallion Fertility Walbornn and colleagues analysed breeding records from 24 Thoroughbred stallions engaged in dual-hemisphere (northern and southern hemisphere) breeding programmes to determine whether dividing a stallion's book across two breeding seasons in opposite hemispheres compromised fertility outcomes. The research examined 11 novice and 13 experienced stallions, comparing pregnancy rates per cycle, first-cycle conception rates, and seasonal fertility alongside mare factors (age, type, number of cycles) and book management variables. Southern hemisphere breeding yielded significantly higher pregnancy rates than northern hemisphere work, but this advantage appeared driven by smaller book sizes and superior mare quality rather than hemisphere-specific effects—notably, book size and total covers showed strong negative correlations with first-cycle pregnancy rate in novice stallions (r = −0.57 and r = −0.71, respectively). Fertility remained unchanged across consecutive dual-hemisphere seasons and proved comparable to single-hemisphere breeding, suggesting no detrimental physiological impact from the divided workload. For practitioners managing stallions in dual-hemisphere programmes, these findings provide reassurance that splitting breeding duties poses no inherent fertility risk, whilst highlighting that breeding efficiency is primarily determined by realistic book sizes and careful mare selection rather than hemisphere allocation.
Read the full abstract on PubMed
Practical Takeaways
- •Dual-hemisphere breeding does not compromise stallion fertility, making it a viable option for managing year-round breeding programs
- •Limiting book size in novice stallions improves pregnancy rates per cycle, particularly important during the first breeding season when managing dual-hemisphere operations
- •Southern hemisphere breeding typically produces better results due to mare quality and lower workload rather than climate or location factors—focus on mare selection and management rather than hemisphere choice
Key Findings
- •Fertility variables were significantly higher in the southern hemisphere compared to the northern hemisphere (P < 0.05)
- •Book size and total number of covers were negatively correlated with first-cycle pregnancy rate in novice stallions (r = -0.57 and r = -0.71 respectively)
- •No adverse effects of dual-hemisphere breeding on fertility were detected when compared to single-hemisphere breeding seasons (P > 0.05)
- •Southern hemisphere breeding success was primarily attributed to smaller book sizes and better mare reproductive quality rather than hemisphere location itself