Effects of GnRH, a progesterone-releasing device, and energy balance on an oestrus synchronisation program in anoestrous dairy cows.

Objective The aim of this research was to study the roles of the day 0 energy balance and gonadotrophin-releasing hormone ( GnRH) and progesterone levels on dominant follicle ( DF) and corpus luteum ( CL) development during the first 7 days of a gonadotrophin-prostaglandin-gonadotrophin ( GPG) + progesterone ( P4) program in anoestrous dairy cows. Methods Cows (n = 81) were allocated to one of the three treatments: (1) GPG + P4 (days 0 and 9, 100 µg GnRH; day 0-7, intravaginal P4 device; day 7, 500 µg PGF_2α); (2) GPG (as for treatment 1 but excluding the P4 device) and (3) prostaglandin + GnRH + P4 (as for treatment 1, but excluding day 0 GnRH). DF and CL size, plasma concentrations of insulin, insulin-like growth factor-I ( IGF-I) and non-esterified fatty acid ( NEFA) were measured on days 0 and 7. Results The proportion of cows with a CL on day 7 was significantly different between groups ( GPG: 78%, GPG+ P4: 69%, PGF_2α + GnRH + P4: 42%, P = 0.02). The CL volume on day 7 was significantly associated with treatment, treatment by time postpartum and plasma concentrations of insulin, IGF-I and NEFA. Conclusion In cows without a CL present on day 0 of an oestrus synchronisation program, removal of the day 0 GnRH treatment led to reduced CL development; however, no effect of adding progesterone was found. In contrast, in cows with a CL present on day 0 inclusion of a progesterone device led to a higher CL volume, but removal of the first GnRH injection had no effect. Response to the treatment was affected by plasma concentrations of insulin, IGF-I and NEFA. [ABSTRACT FROM AUTHOR]