8 EFFECT OF SUPPLEMENTATION WITH ESTRADIOL OR ESTRADIOL PLUS GONADOTROPIN-RELEASING HORMONE AFTER PROSTAGLANDIN F_2α ADMINISTRATION ON THE PREGNANCY RATES FOLLOWING TIMED ARTIFICIAL INSEMINATION IN DAIRY COWS

Abstract

This study determined the effect of supplementation with oestradiol or oestradiol plus GnRH after PGF_2α administration on pregnancy rates after timed artificial insemination (TAI) in dairy cows. Three hundred and six Holstein dairy cows with corpus luteum confirmed by ultrasonography (Tringa Linear with 5.0 MHz array transducer; Esaote Pie Medical, Maastricht, the Netherlands) were randomly allocated to three treatments: a single injection of 500 μg of cloprostenol, PGF_2α analogue (Estrumate, Schering-Plough Animal Health, Friesoythe, Germany; PGF_2α group, n = 115) designated as 0 h, an injection of 500 μg of cloprostenol and an injection of 1 mg of oestradiol benzoate (EB, SY Esrone; Samyang, Seoul, Korea) 56 h later (PGF_2α + EB group, n = 114), or the same treatment as in the PGF_2α + EB group and an additional injection of 100 μg of gonadorelin, GnRH analogue (Godorel, Uni-Biotech Co., Ltd., Korea) 24 h later (PGF_2α + EB + GnRH group, n = 77). All cows in each group received TAI 80 h after the PGF_2α injection. Pregnancy was determined at 40 to 50 days after TAI by using both ultrasonography and rectal palpation. Pregnancy rate among 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 were higher (P < 0.05) in the PGF_2α + EB + GnRH group (34/77, 44.2%) than in the PGF_2α group (31/115, 27.0%), with the PGF_2α + EB group intermediate (39/114, 34.2%). In conclusion, the supplementation with oestradiol plus GnRH after PGF_2α administration improved pregnancy rate after TAI in dairy cows.

This work was supported by the research grant of the Chungbuk National University in 2011.