152 An effective method of inducing oestrus in superovulation-treated Japanese Black donor cows after egg collection

The objective of this study was to evaluate the effect of inducing oestrus in superovulation-treated Japanese Black donor cows after egg collection using a controlled internal drug release (CIDR) device and prostaglandin F2α treatments. The test animals were 50 biparous or triparous Japanese Black cows that had been treated for superovulation during the period of 75-110 days post-calving and from each of which 10 or more ova or embryos had been recovered using a uterine reflux method. In the 25 cows of the control group that received the conventional treatment, a CIDR was not introduced into the vagina, the number of days from egg harvesting to standing oestrus was recorded, and AI was performed using frozen semen. At the time of AI, 50µg of gonadotrophin-releasing hormone (GnRH; Consultan, Aska Animal Health) was administered intramuscularly. The cows that did not conceive in the first AI attempt were again given the same AI and GnRH treatments in the next oestrus cycle. In the 25 cows of the treatment group, a CIDR (CIDR 1900, Zoetis) device was inserted in the vagina after egg harvesting and was kept there for 12 days. At the time of insertion and removal of the CIDR, 150µg of d-cloprostenol formulation (Dalmazin, Kyoritsu Seiyaku) was administered intramuscularly. The number of days from egg harvest to standing oestrus was recorded, and GnRH was administered at the time of AI. The cows that did not conceive in the first AI attempt were given the same AI and GnRH treatments in the next oestrus cycle. The control and treatment groups were compared for the number of days from egg harvesting to oestrus (t-test) and the conception rate after AI (chi-square test). The mean number of days from egg collection to standing oestrus in the control group was 38.6±11.9, and the conception rate was 60% (15/25). Among the animals that failed to conceive in the first AI attempt, the second standing oestrus occurred 60.7±13.1 days after egg collection, and 70% (7/10) of the cows conceived after the second AI. In the treatment group, on the other hand, the mean number of days from egg collection to standing oestrus was 15.8±3.9, and 72% (18/25) of the cows conceived after the first AI. Among the cows that failed to conceive, the second standing oestrus occurred 37.4±4.7 days after egg harvest, and 71% (5/7) of the cow conceived after the second AI. There was a significant difference between the two groups in the number of days from egg collection to the first standing oestrus (P<0.05). The results described above suggest that keeping a CIDR in the vagina for 12 days and intramuscularly administering prostaglandin F2α at the time of insertion and removal of the CIDR in superovulated cows are effective for early onset of standing oestrus after egg collection and thus can reduce the number of days to conception.