Breeding racing mares as early in the season as possible offers a financial incentive to breeders. Doing so means foals born early in the season, and the physical maturity of larger, early foals is in often in greater demand at yearling sales and in 2-year-old races than their later-born counterparts. Early in the breeding season, however, mares are transitioning from winter anestrus to normal ovulatory estrous cycles. During this phase, mares can experience on average 60 to 80 days of erratic estrous behavior and ovulation failure.
In a study conducted over four consecutive breeding seasons involving 227 transitional-phase Thoroughbred mares, researchers in New Zealand examined the effect of an intravaginal progesterone-releasing device (CueMare) on expediting conception early in the season, as well as overall conception rates by the end of the breeding season.
Randomly paired mares were either treated with the progesterone-releasing device or were assigned to an untreated control group. Mares treated with the device were examined after seven days, and the device was removed in those with ovarian follicles of 35 mm or greater. The device remained in place and the mares were re-examined on day ten if the follicle did not reach the required size after seven days.
When mares in either group exhibited estrous behavior in conjunction with ovarian follicles 35mm or greater, researchers administered 1,667 IU human chorionic gonadotropin (hCG) and the mares were subsequently serviced by live cover within 24-36 hours. Ultrasounds performed at 24-hour intervalsdetermine ovulation, followed by further ultrasound at 14 to 16 days after service to determine pregnancy, and again at 28 and 42 days after service to reconfirm pregnancy. Control group mares received biweekly ultrasounds. Mares in both groups that did not initially conceive were examined and served until conception or the end of the breeding season.
The study demonstrated significant differences between mares treated with the intravaginal progesterone-releasing device and those in the control group: 95.2% of treated mares were served within the first 21 days, as opposed to 42.6% of the untreated mares, resulting in earlier breeding in treated mares. Further, 91.3% of treated mares versus 82.3% of control mares conceived by the end of the breeding season.
"The Cue-Mare devices were a cheap and effective method of advancing the onset of the breeding season in mares not exposed to artificial lights," explained Dave Hanlon, BVMS(Hons), PhD, MACVSc, Dipl ACT, a registered specialist in equine reproduction with Matamata Veterinary Services, Ltd. in New Zealand.
The intravaginal route of administration also avoids the need for daily treatment with oral or injectable forms of progesterone, he said. "Further research would focus on comparing the efficacy of Cue-Mare treatment with artificial light exposure," he added.
Jane Stagg, sales manager for Cue-Mare manufacturer Bioniche Animal Health Australia/Asia, said, the device will likely be reviewed for registration/sale in the U.S. market.
This study, "The reproductive performance of Thoroughbred mares treated with intravaginal progesterone at the start of the breeding season," was published in March 2012 in Theriogenology. The abstract is available online.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.