GnRH vaccine could suppress serum progesterone level in Thai pony mares; A preliminary study

Abstract

Colic-like discomfort during periovulatory period was one of the problems affecting athletic performance in horses. Objective of this study was to evaluate level of anti-GnRH antibody and serum progesterone in Thai pony mares after receiving GnRH vaccine. Hypothesis was that mares could produce anti-GnRH antibody, in which endogenous GnRH was neutralized, resulting in anestrus-like serum progesterone level after vaccination. Three Thai pony mares received GnRH vaccine 200 μg intramus-cularly at week 0, 4 and 12. Each horse was examined for some clinical adverse reaction after each vaccination. Blood samples were collected every two weeks, starting from two weeks before first vaccination until week 16. All mares produced anti-GnRH antibody after first vaccination. Anti-GnRH antibody titers peaked at 2 weeks after each vaccination in 2 mares and at 4 weeks in one mare. Characteristic rise of progesterone level after ovulation was not observed in 2 mares from week 4-16, and in one mare from week 8-16. Anti-GnRH antibody titer was adequate to neutralize GnRH, resulting in anestrus-liked progesterone level up to 16 weeks after first vaccination with minimal clinical adverse reaction. The protocol in this study might be able to use for suppression of estrus in Thai pony mares.