One hundred and forty-six Dutch cross Friesian cows were selected from a local slaughterhouse and synchronised with norgestomet. The 134 cows with a normal progesterone pattern after the removal of the norgestomet implant were treated intramuscularly with 3000 iu pregnant mare's serum gonadotrophin (PMSG) on day 10 followed by 22.5 mg prostaglandin 48 hours later. Blood samples were collected daily and at hourly intervals from 30 to 54 hours after the prostaglandin. The 113 cows with a pre-ovulatory peak of luteinising hormone (LH) were divided into three groups: 37 control cows (group 1) received a placebo six hours after the LH peak; 42 cows (group 2) received anti-PMSG six hours after the LH peak and 34 cows (group 3) received anti-PMSG 18 hours after the LH peak. All the cows were inseminated 10 hours after the LH peak. Six or seven days after insemination the cows were slaughtered and the embryos were evaluated after flushing the ovaries, and the numbers of corpora lutea, cysts and follicles on the donor ovaries were counted. Treatment with anti-PMSG had no significant effect on the numbers of corpora lutea or the numbers of embryos compared with the control group. The mean (+/- sem) numbers of corpora lutea were 14.7 +/- 1.4, 16.3 +/- 1.4 and 16.6 +/- 1.4 for groups 1, 2 and 3, respectively. The numbers of transferable embryos were 3.5 +/- 0.6, 4.1 +/- 0.7 and 5.0 +/- 0.7 for groups 1, 2 and 3, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
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