520. RELATIONSHIP BETWEEN THE OVARIAN STATUS ON THE INITIATION DAY OF SUPEROVULATION AND THE OVULATORY FOLLICLES AT ESTRUS IN SHALL IRANIAN EWES

Abstract

The objective of this experiment was to determine the influence of the ovarian status on the initiation day of superovulation (day 14) on superovulatory response in terms of the number of ovulatory follicles (F, ≥4mm) at estrus (day 16). Estrous cycles of 50 Shall Iranian ewes were synchronized by CIDR. The day of CIDR insertion was considered as the starting point of the experiment (day 0). At the time of CIDR removal (day 14), 650 IU of eCG was administered to ewes. Ultrasonography was performed on days 14 and 16. Data were analyzed by means of the GLM procedure of the SAS. In these cases, the number of follicles were determined in each of the three studied classes (<2, 2 to 4, and ≥4 mm) on day 14. Subsequently, each of these classes was divided into two subgroups (Low, High) based on the number of follicles observed on day 14 (Table 1). The number of large follicles at estrus in each of the three studied classes were (3.96±0.28 vs. 4.78±0.26, p<0.05; 4.31±0.35 vs. 4.41±0.24, p>0.05; and 4.50±0.23 vs. 4.07±0.37, p>0.05) respectively. The number of medium and large follicles on day 14 did not affect the superovulatory response. However, the high number of small follicles on the initiation day of superovulation increased the number of ovulatory follicles at estrus. Since, 23 out of 50 ewes had a low number of small follicles on day 14 (Table 1), which may suggest that an injection of FSH 1-2 days before initiation of eCG treatment enhance the superovulatory response.