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

This study investigates the potential harms associated with the usage of intrauterine glass balls (marbles) for suppressing estrus in mares, following some reports of undesirable reproductive consequences. The paper argues for a reconsideration of this practice, in favor of alternative, non-hormonal methods to extend the function of the corpus luteum (CL) and suppress estrous behavior.

Background

• Veterinarians have used intrauterine glass balls for estrus suppression in mares over 10 years. This practice was meant to address behavioral issues related to estrus’ effects on performance, not disease conditions.
• Glass balls are inserted into the mare’s uterine lumen after ovulation to prolong the functioning of the corpus luteum (CL), leading to continued natural secretion of progesterone and subsequent suppression of estrous behavior.
• Short-term use of these devices seemed innocuous. However, recent reports disclosed potential harms associated with their long-term use, such as vulvar discharge, urogenital discomfort, chronic, intermittent colic, to more severe complications like pyometra and glass ball fragmentation.

Use of Glass Balls

• The procedure’s initial attraction stemmed from a desire for non-hormonal methods of estrus suppression, as an alternative to altrenogest, a synthetic progestin often seen as the gold standard for estrus suppression, but expensive, required daily administration, and pose safety risks.
• Research suggested that the glass balls could prolong CL function in mares that retained the balls after insertion, suppressing estrous behavior for approximately 90 days. Results were promising, leading to broad uptake of the method for estrus suppression in mares.

Clinical Concerns

• Case reports noted nine mares experiencing deleterious consequences of glass ball usage, including discomfort, discharge, and more severe health issues. The major issue documented was pyometra – a severe uterine infection, along with glass ball fragmentation.
• A common factor among these concerning cases was the long-term retention of the balls, often due to the insertion of a second ball without knowledge of the preexisting one or the assumption that the first had been expelled.
• The clinical cases call into question the safety of using glass balls for estrus suppression.

Alternative Treatments

• Alternative treatments for prolonging CL function include oxytocin treatment, late-diestrus ovulation induction, intrauterine infusion of plant oils, and pregnancy.
• Notably, treating mares with oxytocin between days 7 to 14 after ovulation seems to be a practical and effective method, inducing prolonged CL function in 60% to 70% of treated mares, suppressing estrous behavior for approximately two months.

Conclusion

• Considering the principle of “doing no harm,” the study suggests it’s prudent to re-evaluate the use of intrauterine glass balls for estrus suppression in mares. It recommends the application of alternative methods to prolong CL function instead.