Morphological and functional characteristics of the dominant follicle and corpus luteum in cattle and their influence on ovarian function

Predicting the functional activity of a dominant follicle (DF) and corpus luteum (CL) might be important before starting a superovulation regime or a synchronization program. The DF and CL were characterized morphologically by using ultrasonography and were characterized functionally by estimating the estradiol-17 beta /progesterone (E-2/P-4) ratio. Their influence on ovarian function was estimated through their ability to ovulate at different stages of development in response to PGF2(alpha)-application. A total of 47 Holstein Friesian (35 cows and 12 heifers) were used in two experiments. In Experiment 1, 25 animals were examined by daily transrectal palpation and ultrasonography to follow the morphological development of the DF. The status of the DF was categorized into 3 groups (A1, B1, C1). The A1 group (n=7) contained animals with DF in the growing phase or in early static growth phase for less than 3 days. Group B1 (n=13) included animals with DF in static growth phase for 3 to 4 days, while Group C1 (n=5) comprised animals with DF keeping a plateau for more than 4 days or animals with DF in the regression phase. The DF were aspirated transvaginally and the follicular fluid (FF) was analyzed for E-2 and P-4. In Experiment 2, 22 animals were included. As in Experiment 1, the animals were classified into three groups (A2, n= 10: B2, n=5. C2, n=7). They were treated by a single dose of PGF(2)alpha (25 mg, im) between Days 8 and 12 of the cycle. Results showed that luteolyses occurred in all animals. The DF, which were in growing or in early static growth phase <3 days were always E-2-dominant (E-2>P-4) and ovulated after PGF2()-application in 6/8 of cases and persisted in 2 (Group A2). The DF persisting >4 days or that had been in regression were always P-4- dominant. This type of DF regressed after PGF(2)alpha -application (Group C2). The DF in early static growth phase for 3 to 4 days in 5/13 cases were E-2-dominant and in 8/13 cases were P-4-dominant. This type of DF ovulated in 3/5 cases and regressed in 2/5 cases after PGF(2)alpha -application (Group B2). These results suggest that the DF is morphologically and functionally defined as long as the DF is in the growing or early static growth phase (A I A2) for at least 2 days or if the DF is in regression (C1, C2). However, when the DF is in the static growth phase for 3 or 4 days (B1, B2), their morphological and functional characteristics are different. The CL controls ovulation in the A and C groups and plays an abettor's roll in the B-group. (C) 2001 by Elsevier Science Inc.