Echotextural changes in the follicular wall during follicle deviation in mares

The echotextural changes occurring in the follicular wall in association wi th deviation in diameters were studied in 8 pony mares. Echotextural change s could be useful as a reference point for future studies of the follicle-s election phenomenon. Follicles were examined daily by transrectal ultrasoun d from 3 d before to 3 d after the beginning of deviation (Day 0). The foll owing echotextural end points were recorded based on a scoring or percentag e system: 1) thickness of granulosa, 2) echogenicity of granulosa, 3) promi nence of an anechoic layer located beneath the granulosa, and 4) extent of involvement of the circumference of the follicle by the anechoic layer. Sig nificant main effects indicated increasing values over Days -3 to 3 and a h igher mean value for the dominant-follicle status for each end point. The i nteraction approached significance for thickness of granulosa and was signi ficant for each of the other 3 end points. The interaction seemed due prima rily to lower values in the subordinate follicle on Days 2 and 3. The first day of an overall echotextural difference between the 2 largest follicles (15.9 +/- 0.5 d after ovulation) or between days within the largest follicl e (16.1 +/- 0.5 d) was about 1 d earlier (P<0.05) than the beginning of dia meter deviation (17.4 +/- 0.8). The effects of follicle diameter versus fut ure follicle status were compared for Days -3 to 0 by grouping follicles fo r each status into 2 diameter categories (16.0 to 18.9 mm and 19.0 to 22.5 mm). Increasing echotextural values for the granulosa (thickness and echoge nicity) were more attributable to follicle growth, whereas the increasing v alues for the anechoic layer were more attributable to status as a future d ominant follicle. Results indicated that development of an anechoic layer b eneath the granulosa distinguished the future dominant follicle from the la rgest future subordinate follicle before the beginning of diameter deviatio n. (C) 1999 by Elsevier Science Inc.