Is it time to retire the use of intrauterine glass balls for estrus suppression in mares?

Abstract

JAVMA, Vol 247, No. 4, August 15, 2015 T ancient medical maxim primum non nocere (first, do no harm) comes to mind when reflecting on the more than 10 years that veterinarians have been using intrauterine glass balls (ie, marbles) for estrus suppression in mares. Although these devices were initially thought to be innocuous, a spate of recent reports has documented the potential for deleterious reproductive consequences associated with their use. In light of these reports, rethinking the use of these devices seems prudent, particularly because they are intended to address a behavioral issue (ie, the real or perceived adverse effects of estrus on performance activities such as showing and racing) rather than a disease condition. Glass balls are inserted into the uterine lumen in an effort to prolong functioning of the CL and allow for continued secretion of progesterone, which suppresses estrous behavior naturally. In nonpregnant mares, the CL secretes progesterone for approximately two weeks after ovulation (ie, the duration of diestrus) and then stops functioning when the endometrium secretes prostaglandin F 2α, causing luteolysis. As a result, serum progesterone concentration falls, and the mare returns to estrus. In 2003, Nie et al reported that placement of a 25or 35-mm-diameter sterile glass ball in the uterine lumen immediately following ovulation resulted in prolonged CL function in 39% of the mares that retained the glass ball after insertion (50% of the smaller glass balls were expelled soon after placement). In those mares that developed prolonged CL function following placement of the glass ball, CL function was maintained for approximately 90 days, during which time serum progesterone concentrations were > 1.0 ng/ mL and estrous behavior was not observed. Clinical interest in the intrauterine glass ball protocol was driven by the desire for nonpharmacological (ie, nonhormonal) methods of estrus suppression that could serve as an alternative to use of the synthetic progestin altrenogest, which is widely considered the gold standard for estrus suppression in mares. Although altrenogest reliably blocks estrous behavior, it is expensive, must be administered daily, and poses safety concerns for personnel who handle the drug. Because of these limitations as well as heightened concerns over the use of exogenous steroid hormones in performance horses, the intrauterine glass ball protocol provided an Is it time to retire the use of intrauterine glass balls for estrus suppression in mares?