Using Estrous Behavior to Time Initiation of Oxytocin Administration to Prolong Luteal Function in Mares.
Authors: Manning Hannah S, Runcan Erin E, Dias de Moraes Christa R, Coutinho da Silva Marco A
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Suppressing oestrus in mares during competition or training seasons remains challenging without prolonging the luteal phase, which naturally lasts only 14–16 days. Manning *et al.* investigated whether oxytocin administration timed to behavioural oestrus could extend luteal function, enrolling 23 light-breed mares (aged 4–20 years) that were teased with a stallion to identify oestrus onset, then randomly assigned to receive either 60 IU oxytocin intramuscularly once daily from days 8–17 post-oestrus (n = 11) or no treatment (n = 12), with serum progesterone monitored until day 45 to confirm corpus luteum function. The oxytocin-treated group demonstrated a significantly longer interestrus interval of 32.4 days compared with 21.8 days in controls (P = 0.01), with over half the treated mares (54.5%) sustaining luteal function beyond 31 days and 45.5% maintaining it to day 45. For practitioners managing performance mares, this protocol offers a practical, behaviour-based approach to oestrus suppression that requires no ultrasound or hormone assay to time treatment initiation, potentially reducing training disruption and improving competitive consistency during critical competition windows. However, considerable individual variation in response suggests that progesterone monitoring remains advisable to confirm efficacy in individual animals, and the modest sample size warrants validation in larger cohorts before widespread protocol adoption.
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Practical Takeaways
- •Estrous behavior observation alone can reliably time an oxytocin protocol (60 IU daily, Days 8-17 post-estrus) to suppress estrus and extend the luteal phase by 10+ days in most mares
- •This approach offers a practical, cost-effective alternative to other estrus suppression methods that does not require frequent blood sampling or ultrasound for protocol timing
- •Approximately half of treated mares will maintain luteal function for extended periods (up to 45 days), providing reproductive management flexibility for competition or breeding schedules
Key Findings
- •Once-daily oxytocin (60 IU IM) administered from Day 8-17 after behavioral estrus increased average interestrus interval from 21.8 to 32.4 days (P = .01)
- •54.5% of treated mares (6/11) achieved interestrus intervals longer than 31 days, with 45.5% (5/11) extending to 45 days
- •Luteal phase prolongation beyond 30 days was successfully attained in a majority of oxytocin-treated mares using estrous behavior alone to time treatment initiation
- •Timing oxytocin administration to begin 8 days after observed behavioral estrus is an effective protocol for estrus suppression