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 l uteum (CL) might be important before starting a superovulation regime or a synchronization program. The DF and CL were characterized morphologically b y using ultrasonography and were characterized functionally by estimating t he estradiol-17 beta /progesterone (E-2/P-4) ratio. Their influence on ovar ian function was estimated through their ability to ovulate at different st ages of development in response to PGF2(alpha)-application. A total of 47 H olstein Friesian (35 cows and 12 heifers) were used in two experiments. In Experiment 1, 25 animals were examined by daily transrectal palpation and u ltrasonography to follow the morphological development of the DF. The statu s 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 ph ase for less than 3 days. Group B1 (n=13) included animals with DF in stati c 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 regres sion 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 luteolys es occurred in all animals. The DF, which were in growing or in early stati c growth phase <3 days were always E-2-dominant (E-2>P-4) and ovulated afte r PGF2(<alpha>)-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- d ominant. 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 i n 3/5 cases and regressed in 2/5 cases after PGF(2)alpha -application (Grou p B2). These results suggest that the DF is morphologically and functionall y 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). Howeve r, when the DF is in the static growth phase for 3 or 4 days (B1, B2), thei r morphological and functional characteristics are different. The CL contro ls ovulation in the A and C groups and plays an abettor's roll in the B-gro up. (C) 2001 by Elsevier Science Inc.