Reproduction Abstracts

Introduction: Clomiphene citrate belongs to group of drugs known as selective estrogen receptor modulators. In this study, an attempt was made to induce ovulation in crossbred prepubertal heifers by the use of clomiphene citrate and hCG. It was hypothesized that clomiphene citrate, being antiestrogen, would remove negative feedback effect of estrogen on the release of pituitary gonadotropins. Elevated gonadotropins would support follicular growth to a point where hCG would induce ovulation.

Materials and methods: Six prepubertal Sahiwal×Friesian heifers were orally given clomiphene citrate at 300 mg/heifer for 9 days. Another six heifers served as control. On the 10th day, hCG was given to all heifers at 2500 IU. Blood was collected on alternate days up to 14 days after hCG injection, starting from 1 day before start of treatments and plasma was assayed for progesterone and estradiol concentrations.

Results and discussion: Mean estradiol level prior to start of treatment was below 3 pg/ml in heifers of the two groups. This pattern persisted for the first 6 days of treatment, during last 3 days of treatment estradiol level rose, reaching peak of 16.20±8.74 pg/ml on day of hCG injection in four heifers of treatment group. After hCG injection, mean estradiol level of treated group gradually dropped and progesterone level rose. In control heifers, mean estradiol concentration remained >4 pg/ml throughout the experiment. Progesterone assay showed that four heifers (67%) in treated group ovulated (P4 >1 ng/ml plasma) compared to one heifer (16%) in control group. In conclusion, clomiphene citrate along with hCG can be used to induce ovulation in prepubertal heifers.