An intravulvosubmucous injection of prostaglandin F 2α in anoestrous cows

Abstract

Anoestrous cows with a prolonged corpus luteum were subjected to an intravulvosubmucous injection of prostaglandin F 2α (PGF 2α) (2, 4 or 6 mg). Oestrous responses and the subsequent fertility to different doses of PGF 2α were compared. The plasma progesterone of 10 cows treated with 2 mg of PGF 2α was measured by the radioimmunoassay (RIA) method and the peripheral levels immediately before and 4 days after treatment were compared. A total of 79 anoestrous cows was randomly injected with one of the three doses of PGF 2α. The proportions of cows showing oestrus within 7 days of treatment were 37.9% (11/29), 58.3% (21/36) and 78.6% (11/14) for 2, 4 and 6 mg, respectively. There was a significant difference between the groups which received 2 and 6 mg ( P < 0.05). No significant difference was found in the proportions of cows showing oestrus within 3 days of each treatment. The pregnancy rates 60–90 days after artificial insemination (A.I.) with frozen-thawed semen did not show significant differences among the doses of PGF 2α (72.7%, 57.1% and 81.8% for 2, 4 and 6 mg, respectively). In 6 of 10 cows treated with 2 mg PGF 2α, the plasma progesterone clearly declined on the 4th day after treatment, but the oestrous response was observed only in 4 of those 6 cows. The present study indicates that an intravulvosubmucous injection with less than 6 mg PGF 2α is an effective method of inducing oestrus and subsequently satisfactory fertility in anoestrous cows with a prolonged corpus luteum.