This study compared pregnancy rates following 2 timed artificial insemination (TAI) protocols using PGF2α + oestradiol or PGF2α + oestradiol + GnRH in dairy cows. Four hundred fifty-five Holstein dairy cows, 2.2 ± 0.1 in parity, 148.3 ± 3.6 days in milk, with corpus luteum of greater than 20 mm diameter confirmed by ultrasonography (Tringa Linear with 5.0 MHz array transducer; Esaote Pie Medical, Maastricht, the Netherlands) were randomly divided into two treatments: an injection of 500 μg of cloprostenol, PGF2α analogue (Iliren cycle BP®, Intervet International GmbH, Unterschleissheim, Germany) and an injection of 2 mg of oestradiol benzoate (EB, SY Esrone, Samyang, Seoul, Korea) 36 h later (PGF2α + EB group, n = 257), or an injection of 500 μg of cloprostenol, an injection of 2 mg of EB 36 h later and an additional injection of 100 μg of gonadorelin, GnRH analogue (Godorel, Uni-Biotech Co., Ltd., Korea) 24 h later (PGF2α + EB + GnRH group, n = 198). All cows in the two groups received TAI 24 h after the EB injection. Pregnancy was determined at 40 to 50 days after TAI by using both ultrasonography and rectal palpation. Pregnancy rates between the PGF2α + EB and PGF2α + EB + GnRH groups were compared by the chi-square test using the SAS program (version 9.1: SAS Institute Inc., Cary, NC, USA). Pregnancy rate following TAI did not differ between the PGF2α + EB (32.7%) and PGF2α + EB + GnRH groups (34.9%; P > 0.05). In conclusion, addition of GnRH for TAI protocol using PGF2α + oestradiol did not improve pregnancy rate in dairy cows.
The GnRH analogue dephereline given in a fixed-time AI protocol improves ovulation and embryo survival in dairy cows
