Efficacy of gonadorelin hydrochloride or gonadorelin diacetate tetrahydrate 7 days after AI in field conditions to boost progesterone levels, a randomized clinical trial

Abstract

The ability of some reproduction synchronization protocols to increase conception rates (CR) is reported as being in part due to increased progesterone (P4) levels in the diestrus phase before breeding. This has been demonstrated mostly in an experimental context and was linked to GnRH increasing the proportion of cows luteinizing a second corpus luteum (CL). A pilottrial was conducted to determine if an injection of gonadorelin hydrochloride (Factrel®) or gonadorelin diacetate tetrahydrate (Cystorelin®) given 7 days after AI to all cows on a farm in field conditions resulted in a significant increase of P4 levels 14 days after AI, compared to a placebo. If an increase in P4 levels was to be observed, a second larger trial was to be conducted testing the effect of post-AI GnRH on CR at return to estrus.