86 Ultrasonographic evaluation of preovulatory follicle and endometrial echo texture for ovulation prediction in Marwari mares

Abstract

The objective of the present study was to evaluate the application of ultrasonographic changes in the preovulatory follicle and uterus for ovulation prediction in Marwari mares. Mares (n=20) were teased daily by a teaser pony and, from the day of first detected oestrus, the ovaries and uterus were examined by transrectal ultrasonography using Exago ECM ultrasound equipped with linear rectal probe (10MHz) until ovulation. Recorded data were analysed by one-way ANOVA and correlation coefficients. The duration of the oestrus period ranged from 5 to 7 days in all mares, with an average of 6.35±0.13 days, consistent with rectal findings. The last day of oestrus was marked by disappearance of the preovulatory follicle and presence of a corpus haemorrhagicum. The mean diameter of the follicles increased significantly (P<0.01) from Day 1 to Day 7, and the diameter of follicles before ovulation was 44.88±0.46 mm; follicles changed from round to oval or irregular before ovulation. In 65% (13/20) of the mares, ovulation occurred on the left ovary. The daily mean growth rate of size of ovulating follicles from the first day of oestrus until ovulation was 3.51±0.42 mm/d. The mean average growth rate of follicles was significantly different (P ≤ 0.01) on different days of oestrus. The mean endometrial echo texture score was 1.30±0.10 on Day 1, 2.10±0.16 on Day 2, 3.20±0.15 on Day 3, and highest 3.85±0.08 on Day 4, declining thereafter to reach a score of 1.36±0.11 on Day 7 of the oestrous cycle. The mean slope values of pixel intensity for the granulosa and anechoic layers of the preovulatory follicles determined by Image-Pro software (Media Cybernetics) from Days −3 to −1 was 13.8±0.7 on Day −3, 15.7±0.9 on Day −2, and 20.1±1.3 on Day −1. None of the follicles ovulated before granulosa layer echogenicity reached a score of ≥2.5 and prominence of anechoic layer reached a score of ≥2. Significant positive correlations were found between the cross-sectional diameter of the uterine horn and estrual endometrial echotexture score (P<0.01; r=0.95), estrual endometrial echo texture score and preovulatory follicle diameter (P<0.01; r=0.25), and preovulatory follicle diameter and cross-sectional diameter of uterine horn (P<0.01; r=0.36) during the oestrous cycle. We conclude that various ultrasonographic characteristics of preovulatory follicle and uterus can be used to predict ovulation in Marwari mares.