PARENT SESSION

(W639) DEVELOPMENT OF A MODEL FOR OVULATION OF FOLLICLES ORIGINATING FROM DIFFERENT FOLLICULAR WAVES IN EWES.

Wurst, A.¹, Knights, M., Dailey, R., Inskeep, E., ¹ West Virginia University, Morgantown, WV

ABSTRACT- When ultrasonographic analysis is limited to follicles that grow from 3 to 5 mm, follicular waves can be identified in sheep. In most cases, ovulatory follicle(s) develop from the ultimate follicular wave, however, ovulatory follicles can be derived from penultimate or earlier follicular waves. The relationship between follicular lifespan and fertility is controversial in sheep. Two approaches to create a model to compare fertility when ovulatory follicles develop from only the ultimate follicular wave (U) or both U and penultimate (P) waves were tested. In exp. 1, ovaries of mature ewes (n = 24) were scanned by ultrasonography daily from d 7 of the estrous cycle until ovulation. Ewes (n = 11) were treated on d 11 with 50 g of GnRH i.m. in an attempt to cause ovulation, luteinization, or regression of largest follicle(s). Corpora lutea (CL) were counted by ultrasound 7 d following estrus in order to verify ovulation of follicles that disappeared post estrus. Pregnancy was determined and embryos were counted 23 to 28 d following ovulation. GnRH caused estrus and ovulation in 3 of 11 ewes treated. Treatment with GnRH did not remove more of the 3 largest penultimate follicles (≥ 4 mm) in treated ewes (atresia of 22 of 33) than in controls (atresia of 19 of 29). In exp. 2, (n = 29) the largest follicle (≥ 4 mm) and the second largest follicle(s) (≥ 4 mm, 2 in case of a tie) on each ovary were electrocauterized on d 11 in treated ewes (n = 15), and controls (n = 14) underwent sham surgery. After follicular ablation, 100% of ovulations in treated ewes were from U vs. 64% in control ewes (exp. 2) and 71% of all ewes in exp. 1 (p = 0.01). Ovulation rate in exp.1 was 2.0, whereas ovulation rates in exp. 2 were 1.6 and 1.5 for control and treated ewes, respectively. In exp. 2, average age (d from detection at 3 mm) of the ovulatory follicle was 5.1 days in both control and treated groups. In control ewes, average age of ovulatory P follicles was 7.4 days versus 4.3 days for U follicles (p < 0.01). Five of 22 and 7 of 23 CL were not represented by embryos on d 23 to 28 in control and treated groups, respectively. Cauterization of largest follicle(s) on d 11 allowed creation of a model to study effects of ovulation of follicles that originated from different follicular waves on fertility in ewes. (Supported by Hatch 427 (NE 1007) and a WVU Foundation Swiger Fellowship to AW)

KEY WORDS: OOCYTE MATURATION, EWE, FERTILITY, FOLLICULAR DYNAMICS