Reversibility of the effects of GnRH-vaccination used to suppress reproductive function in mares.
Authors: Schulman M L, Botha A E, Muenscher S B, Annandale C H, Guthrie A J, Bertschinger H J
Journal: Equine veterinary journal
Summary
# Editorial Summary: Reversibility of GnRH-vaccination in mares GnRH-vaccination (using Improvac) offers equine practitioners a reversible method for suppressing oestrous behaviour and fertility, but the timeline for recovery of reproductive function had not been clearly established until this South African study. Researchers vaccinated mares across three age categories twice (35 days apart) with 400 µg Improvac and tracked suppression and recovery via progesterone concentration and anti-GnRH antibody titres over two years. All mares achieved complete ovarian suppression by Day 70, and 92.2% resumed cyclic activity by Day 720, with median recovery at 344 days (range 232–488 days)—notably, younger mares (≤4 years) required significantly longer for fertility restoration than older animals (≥11 years), despite similar antibody responses. These findings provide practitioners with reliable expectations for reversibility and demonstrate that age should be considered when planning vaccination schedules, particularly for younger mares where a year-long period without cycling should be anticipated before breeding is possible again.
Read the full abstract on PubMed
Practical Takeaways
- •GnRH-vaccination can reliably suppress oestrous behaviour in mares for extended periods (mean ~418 days), making it a practical reversible alternative to surgical castration or other permanent methods
- •Plan for complete recovery of fertility to take 7-16 months post-vaccination, with younger mares requiring longer recovery periods, necessitating longer-term planning for breeding programmes
- •This vaccine provides a reversible reproductive management tool for mares of all ages, offering flexibility for future breeding decisions without permanent alteration
Key Findings
- •All mares achieved suppression of cyclic ovarian activity by Day 70 post-vaccination with serum progesterone ≤1 nmol/l
- •92.2% of mares resumed cyclic ovarian activity by Day 720 with mean interval of 417.8 days (range 232-488 days, median 344 days)
- •Significant age effect observed with youngest mares (≤4 years) showing longer interval to reversibility compared to oldest mares (≥11 years, P=0.028)
- •GnRH-vaccination with Improvac provides reversible, reliable suppression of ovarian function in mares across all age categories