Ovarian function and pregnancy outcome in pony mares following immunocontraception with native and recombinant porcine zona pellucida vaccines.
Authors: Joonè C J, Bertschinger H J, Gupta S K, Fosgate G T, Arukha A P, Minhas V, Dieterman E, Schulman M L
Journal: Equine veterinary journal
Summary
# Editorial Summary Zona pellucida immunocontraception represents a promising reversible alternative to surgical castration or long-term hormonal suppression in mares, yet concerns remain about unintended effects on reproductive function. Researchers conducted a randomised controlled trial comparing conventional porcine zona pellucida (pZP) vaccine with a novel recombinant formulation (reZP) in 21 pony mares, monitoring ovarian activity via weekly transrectal ultrasound and serum hormone analysis over 24 weeks, whilst breeding attempts were made via artificial insemination following vaccination. The pZP vaccine produced profound contraceptive effects, with 86% of treated mares entering extended anoestrus with suppressed oestradiol and progesterone levels and zero successful pregnancies, whereas the reZP vaccine proved substantially less effective, achieving only 14% anoestrus and a 57% pregnancy rate comparable to controls. Although ovarian function remained reversible and all mares resumed normal cycling within 10 months, the marked difference in efficacy between formulations and the association between pZP immunisation and oestrous suppression merit careful consideration when selecting immunocontraceptive protocols; practitioners should counsel clients that pZP may compromise breeding intentions for an extended period, whilst reZP warrants further investigation as potentially offering a more balanced contraceptive–fertility profile. These findings underline the importance of individualised reproductive management planning, particularly for valuable breeding stock or mares where temporary fertility preservation is a priority.
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Practical Takeaways
- •pZP immunocontraception in mares causes predictable but reversible suppression of ovarian cycling, with 86% developing anoestrus; plan breeding accordingly and expect 10-month recovery period
- •The newer recombinant reZP vaccine shows lower contraceptive efficacy (86% vs 14% anoestrus rates) but better preservation of fertility; choose vaccine type based on breeding vs. contraception priorities
- •If breeding pony mares within 10 months of pZP vaccination, expect significantly reduced pregnancy rates; consider timing of vaccination relative to breeding season
Key Findings
- •86% of pZP-vaccinated mares (6/7) developed extended anoestrus compared to 14% of reZP mares (1/7), with suppression correlating with basal oestradiol and progesterone levels
- •All immunocontracepted mares resumed cyclicity by 10 months post-treatment, demonstrating reversible ovarian suppression
- •Pregnancy rates were 100% in controls, 57% in reZP-treated mares (4/7), and 0% in pZP-treated mares (0/7) over 2 consecutive oestrous cycles
- •Native pZP vaccine demonstrated superior contraceptive efficacy compared to novel recombinant reZP vaccine but with greater ovarian dysfunction