Non-inferiority randomized field clinical trial of two GnRH commercial products used in a systematic double-ovsynch protocol at first breeding in dairy cows

The use of the double-ovsynch (DBLOV) protocol at first service in dairy herds has become more popular in dairy practice because of its potential to increase the conception risk (CR), especially in primiparous cows, compared with usual ovsynch or presynch protocols. The use of the DBLOV protocol implies giving four injections of commercial GnRH products to each cow. Previous studies have raised issues about the efficacy of GnRH hydrochloride (Factrel®, Zoetis Animal Health) to induce ovulation compared with other GnRH forms. However, few studies have reported CR when using the DBLOV protocol in a large number of dairy cows under field conditions. The objective of this study was to compare CR at first service when using GnRH hydrochloride (Factrel®) or GnRH acetate (Fertiline®, Vetoquinol) in a systematic DBLOV protocol in dairy cows under field conditions. The hypothesis was that there would be no significant difference between first-service CR between both GnRH forms.