Reinforcement breeding: Ensuring mares are successfully bred
For natural cover breeding programs, as is required in Thoroughbred horses, techniques can be used to help maximize pregnancy success. One such technique is reinforcement breeding.
While stallion management can be accomplished by reviewing stallion breeding records and habits, reinforcement breeding is a technique to help ensure mares are successfully bred, especially since there's variability of the natural covering habits of certain stallions.
Reinforcement breeding (sometimes called impregnation) involves obtaining a dismount sample from the stallion's penis immediately after mating and infusing that dismount sample into the uterus of the mare just mated.
"Proponents for the process claim fertility is improved, perhaps because of an increased number of sperm accessing the uterus for transport to the oviducts. Others claim the number of sperm recovered in dismount samples is too small and the quality of sperm too poor (e.g., due to cold and osmotic shock and contamination with debris) to improve fertility of most matings," says Terry Blanchard, DVM, MS, Dipl. ACT, professor in the Department of Large Animal Clinical Sciences at Texas A&M University's College of Veterinary Medicine and Biomedical Sciences.
"I think reinforcement breeding is useful in most situations, especially when stallions have large books of mares to which they're being bred, where sperm numbers placed in the uterus could be marginal," says Blanchard's colleague Dickson D. Varner, DVM, MS, Dipl. ACT, professor of theriogenology and Pin Oak Stud Chair in Stallion Reproductive Studies also at Texas A&M University.
Varner recommends maintaining the dismount semen sample at body temperature, straining it through a filter to remove extraneous debris, and then mixing the semen with a small volume of a good-quality extender. The semen is then introduced via a pipette passed through the vagina and then discharged directly into the uterine body. The semen must be grossly devoid of urine and blood.
"As the stallion comes off the mare, postbreeding, one of the stallion handlers will essentially milk the penis in a cup and collect that sample," says Pete Sheerin, DVM, Dipl. ACT, Rood & Riddle Equine Hospital, Lexington, Ky. "Some stallions are very efficient when they ejaculate, and there's no sperm from the dismount—not enough to justify using the sample."
Sometimes the remnants of the ejaculate, present in the vagina, are evacuated and reintroduced, along with additional semen, directly into the mare's uterus. "The vaginal technique depends on the stallion and mare," Sheerin says. When the stallion ejaculates, if it proceeds as it should, the stallion ejaculates directly into the uterus. "In a stallion that breeds normally and stays on the mare until he's finished ejaculating, when you insert a speculum in that mare's vagina to obtain a sample, the odds are you won't find anything."
Another stallion, however, might back off from a mare before it is finished ejaculating. Normally when a stallion ejaculates, there are five to seven jets of semen. "A horse may deposit four of them directly into the mare's uterus and, as it is coming off, leave the other three in the vagina," says Sheerin. This semen can then be reintroduced into the uterus.
Blanchard explains, "Since debris from the mating process and breeding shed floor can get into dismount samples, we believe it is wise to first filter the dismount semen sample to remove as much debris or dirt as possible, as well as to immediately mix the dismount semen sample with a suitable volume of warm extender that contains a broad-spectrum antibiotic, prior to infusion of the dismount sample into the uterus of the mare."
He notes the process might improve fertility. First, it results in an increased number of sperm placed directly into the uterus. Second, the extender could provide some protection to sperm that may improve their longevity within the uterus until they can access the oviduct where fertilization occurs. Finally, the antimicrobial present may help to control postbreeding endometritis.