This study aimed to determine whether progesterone from intravaginal insertion of a CIDR device could substitute for luteal progesterone and facilitate oestradiol benzoate (ODB)-induced control of ovarian follicle waves in the event of luteolysis. Luteolysis was induced by an injection of prostaglandin-F2a on Day 13 of the oestrous cycle in 24 lactating dairy heifers. Concurrent treatments on Day 13 were: i) 1 mg ODB i.m. (ODB1); ii) CIDR for 6 days (CIDR); iii) 1 mg ODB i.m. plus CIDR for 6 days (ODB1/CIDR); or, iv) 2 mg ODB i.m. plus a CIDR for 6 days (ODB2/CIDR). Examination of the ovaries using ultrasonography showed that oestrous cycles comprising 2 follicle waves predominated among ODB1 and CIDR groups; whereas combination treatments produced mostly 3-wave cycles (p<0.05). Day of ovulation was 15.4 ± 0.3, 21.2 ± 0.2 and 22.5 ± 0.2 for ODB only, CIDR only and 1 or 2 mg ODB plus CIDR cows, respectively (p<0.01). The interval from day of emergence to ovulation of the ovulatory follicle was less (p<0.01) in cows treated with ODB only (6.0 ± 0.3 days), or ODB plus a CIDR (7.2 ± 0.6 days), compared to a longer interval in those receiving a CIDR only (11.0 ± 0.8 days). These results showed that progesterone from a CIDR device was able to facilitate ODB-induced follicle wave turnover at the time of luteolysis in lactating dairy heifers.

CR, Burke, S Morgan, BA Clark, and FM Rhodes

Proceedings of the New Zealand Society of Animal Production, Volume 58, , 89-91, 1998
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