Stallion management has a major impact on the success of a breeding program. | Adobe StockStallion management is an underserviced area, yet subfertility or infertility has a vast effect on the success of a breeding plan, said C. Scott Bailey, DVM, MS, Dipl. ACT, associate professor at Cornell Universitys College of Veterinary Medicine, in Ithaca, New York. Bailey described key management factors veterinarians should evaluate in live cover stallions during his presentation at the 2025 American Association of Equine Practitioners Convention, held Dec. 6-10, in Denver, Colorado.While mare management often dominates reproductive discussions, Bailey emphasized that overlooking the stallion can derail an entire breeding season. From anatomy and physiology to housing and behavior, small management gaps can have significant fertility consequences.Understanding Stallion Anatomy and Fertility TimelinesPuberty in male horses typically occurs between 12 and 24 months, with full sexual maturity between 4 and 5 years old. Breeding stallions prior to two to three years of age can result in subfertility and long-term behavior problems, Bailey noted.He said the glans penis enlarges markedly during erection, and ejaculation occurs directly into the uterus. The testicles lie horizontally within the scrotum, and rotation or torsion up to 180 degrees can be normal during breeding.Trauma to the penis and scrotum are common with live cover and often emergent, said Bailey. Seminal vesiculitis (inflammation or infection of the seminal vesicles, which are the structures that produce semen) can also occur and rarely, a blocked ampulla (a disorder in which accumulated dead sperm obstruct the widened end of the vas deferens, which is the conduit of sperm) or urethral tears. Timing also matters following illness or injury. After a systemic disease event or testicular insult, it takes 66 to 71 days for newly produced sperm to appear in the ejaculate. So, there will be a period of subfertility.Natural vs. Managed Stallion BehaviorBailey contrasted modern stallion housing with feral social structures. In natural bands one or two mature stallions maintain a harem of mares, while bachelor bands consist of displaced or younger males. Importantly, testosterone production is closely related to the presence of mares, said Bailey. Harem stallions have twice the testosterone of bachelor stallions. But within one week of a stallion entering a harem, they will produce 200% the testosterone, and vice versa with a stallion displaced from harem. In addition, as in mares, photoperiod influences stallions reproductive hormones.Under natural conditions stallions approach mares head-to-head. Mares in estrus reposition themselves, and stallions might mount without erection. After breeding, the mare simply walks away.In contrast, managed stallions are often housed in isolation with limited exercise and minimal contact with maressometimes even less social interaction than a bachelor stallion.Natural mating is anything but natural to a managed stallion compared to the feral situation, said Bailey. Managed stallions have minimal physical contact with mares, and we do not even allow penetration without some sort of barrier, such as a matted panel, between the mare and stallion.Modern expectations are also compressed: erection within two minutes, mounting within seconds, limited thrusts, and ejaculation on the first attempt. When that sequence falters, problems such as poor libido, mounting issues, aggression, incomplete ejaculation, or urine contamination of semen might arise.Practical Stallion Management Tips to Improve Breeding SuccessOne way to mitigate these issues is by changing housing, said Bailey. We can imitate a harem by pasturing mares close by, allowing visual and olfactory contact with mares but not other stallions. Stallions with behavior problems can be reversed with patience, time, and confidence.His additional management recommendations included:Maintain a consistent schedule, environment, and personnel. But sometimes you need to change the environment to reset the stallions behavior, such as moving from the breeding shed to the field, said Bailey.Ensure the mare is in strong estrus, particularly for young or problematic stallions.Allow safe physical contact between the stallion and mares when appropriate depending on the individual horses and those handling them.Correct unsafe behavior in a way that avoids negative breeding associations.Keep detailed records of breedings and use them to assess performance.Analyze semen, including post-breeding samples, to confirm sperm concentration and motility along with absence of blood or urine.Perform genital cultures every 10 mares to screen for sexually transmitted disease.In some situations, Bailey said adding semen extender after breeding might offer some benefitsfor example, when sperm quality is suboptimal or subclinical infections are suspected, because extenders contain antibiotics and can help move residual sperm toward the oviducts. He also noted that a newer technique called deep-horn reinforcement, modeled after deep uterine horn insemination used elsewhere in the industry, has not been shown to improve outcomes in stallions used for live cover.Take-Home MessageWhen conception rates dip, attention often turns immediately to the mares. Bailey emphasized the importance of stallion physiology, social environment, behavior, and handling protocols for fertility outcomes.Subfertility is rarely random, ?he said?. By aligning management more closely with biology and by critically evaluating housing, behavior, and semen quality, veterinarians and breeding farm managers can improve live cover success and protect the long-term reproductive soundness of valuable stallions.