MONITORING OVARIAN RESPONSE OF BOOROOLA ASSAF EWE LAMBS TO PMSG, USING ULTRASONOGRAPHY AND SERUM ESTRADIOL

Ovarian size was determined for 30-day-old ewe lambs treated with pregnant mare serum gonadotropin (PMSG; 1000 IU) using ultrasonography and was compared with direct measurement at laparotomy. Ultrasonography was found to be an accurate and reliable method for estimating ovarian size, and a significantly high correlation was found between the methods (R = 0.96, P<0.01). Forty-eight hours following PMSG treatment, serum estradiol levels increased from below detectable levels to a value of 72.8 +/- 27.4 pg/ml (mean +/-SEM). A high correlation was found also between estradiol levels and ovarian size measured at laparotomy and by ultrasound, with a correlation coefficient of 0.94 and 0.80, respectively. It is suggested that a differential increase in ovarian size and estradiol secretion in immature ewe lambs treated with PMSG may reflect the different stages of ovarian development in individual animals. Noninvasive methods such as ultrasonography and measurements of serum estradiol may be utilized in the estimation of ovarian response.