Effect of intrauterine administration of gonadotropin releasing hormone with glycerol on serum LH concentrations in lactating dairy cows

Abstract The objectives of the study were to assess: (1) preovulatory serum LH concentrations and (2) synchrony of ovulation after im or iu administration of GnRH with or without the addition of glycerol. Cows were presynchronized with 2 injections of PGF 2α given 14 d apart (starting at 26 ± 3 DIM) followed by Ovsynch (OV; GnRH-7 d-PGF 2α -48 h-GnRH) 12 d later. At the time of the second GnRH of OV (GnRH2), cows were blocked by parity and randomly allocated to 1 of 4 treatments: (1) control (CON; n  = 8) received 2 mL of sterile water im; (2) im (IM; n  = 8) received 100 μg of GnRH im; (3) cows were infused with 200 μg GnRH into the uterus (IU; n  = 9); and (4) iu administration of 200 μg GnRH plus glycerol 7% v/v (IUG; n  = 8). Serum circulating progesterone concentrations at hour 0 did not differ ( P  > 0.05) among groups. Concentrations of LH were greater ( P