181 COMPARISON OF THE PREGNANCY RATES AFTER SYNCHRONIZATION OF OVULATION USING GnRH AND PGF2α IN RECIPIENT DAIRY CATTLE
T. Nishisouzu A , M. Sugawara C , S. Aoki A , K. Kishida A , M. Moriyoshi B , M. Moriyoshi B , O. Dochi A and H. Koyama AA Department of Dairy Science, Rakuno Gakuen University, Ebetsu, Hokkaido, Japan. email: dochi@rakuno.ac.jp;
B School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkaido, Japan;
C AK farm, Syowa, Gunma, Japan.
Reproduction, Fertility and Development 16(2) 212-213 https://doi.org/10.1071/RDv16n1Ab181
Submitted: 1 August 2003 Accepted: 1 October 2003 Published: 2 January 2004
Abstract
Treatments with GnRH and PGF2α for synchronization of ovulation has resulted in acceptable pregnancy rates after fixed-time artificial insemination in dairy cows without estrus detection. The objective of the present study was to evaluate the practicability of ovulation synchronization (Ovsynch, Pursley JR et al. 1995 Theriogenology 44, 915–923) in dairy cattle using GnRH and PGF2α for the embryo transfer recipients. Dairy cattle (cows; n = 100, heifers; n = 88) were randomly allocated to one of two groups. The control group (cows; n = 45, heifers; n = 37) was composed of cows in natural estrus. The ovulation synchronization group (cows; n = 55, heifers; n = 51) was treated with an intramuscular injection of 100 μg of GnRH at a random stage of the estrous cycle. Seven days later, the cattle received PGF2α (Cows; 25–30 mg) or PGF2α analog (Heifers; 0.5 mg) in order to regress the corpora lutea (CL). Forty-eight hours later, cows and heifers received a second injection of 100 μg GnRH. Embryo transfer was carried out 7 days after the second injection of GnRH in the ovsynch group and 7 days after estrus in the control group. The cattle judged to have CL 17 mm were classified as acceptable recipients. The size of the follicles and the CL were determined to be of estrus stage and embryo transfer by means of ultrasonography. The mean numbers of follicles and CL were analyzed by ANOVA, while pregnancy rates were analyzed by chi-square test. The results are presented in the Table. The proportion of cows and heifers determined to be acceptable embryo transfers was not different between the control group and the ovsynch group. There were no differences in the proportion of acceptable embryo transfers between the control group and the ovsynch group. Follicle diameter at the time of estrus in the control group (cows; 20.7 ± 0.7 mm, heifers; 16.8 ± 0.5 mm) were significantly larger than that of the ovsynch group (cows; 18.0 ± 1.0 mm, heifers; 14.7 ± 0.2 mm) (P < 0.05). Although CL diameter at the time of embryo transfer in heifers showed no differences between the control group and the ovsynch group (25.0 ± 1.0 mm v. 22.8 ± 1.5 mm), The CL diameter of the control cow group was larger than that of the ovsynch group (29.8 ± 0.7 mm v. 26.1 ± 1.0 mm, P < 0.05). However, no differences in pregnancy rate were seen between the control group and the ovsynch group. These results suggest that ovsynch can be effectively applied in an embryo transfer program for cattle.
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