Effects of placement of intravaginal sponges on LH, FSH, estrus and ovarian activity in mares during the nonbreeding season.

This research article is a study on how placing intravaginal sponges impacts reproductive hormones and behaviors in mares during their nonbreeding season. It concluded that sponge treatment can induce hormone surges and increase ovarian size, but does not prove to be an efficient method to prepare mares for synchronized progestogen treatment.

Experiment Setup

• For the experiment, eight mares that were in their nonbreeding season, known as anestrus, were administered intravaginal polyurethane sponges. This phase started on December 15 and continued weekly until February 1st.
• A group of control mares were kept without any sponges or genital contact for comparison.

Results of Sponge Placement

• Following the insertion of sponges, 50% of the treated mares experienced a sudden increase in the concentration of the follicle-stimulating hormone (FSH) in their blood, compared to none in the control group.
• The treatment’s effect on luteinizing hormone (LH) concentrations was less significant, with only three mares from the treated group showing positive responses.
• The researchers noted that the strength of the FSH response declined quickly with each subsequent response.

Effects on Estrus and Ovarian Activity

• The introduction of the sponges induced estrus, a phase in the animal’s menstrual cycle when ovulation occurs, in half of the treated mares. In contrast, no mares from the control group exhibited estrus.
• The treatment also caused an increase in the size of the mares’ ovaries and the occurrence of large follicles.

Impact on Altrenogest Treatment

• All mares, including both treated and control groups, were fed altrenogest—a synthetic progestogen for 14 days starting February 1. The researchers found the previous sponge treatment had no positive effect on the number of mares that exhibited estrus or the pregnancy rate during this time.

Conclusion

• The research confirms earlier speculation that sponge treatment does cause surges in gonadotropins (hormones that stimulate the gonads) and increases the size of the ovaries in around 50% of anestrus mares. However, it did not appear to be a practical method to prepare mares for progestogen synchronization outside the breeding season.