Ultrasonography of the bovine ovary

A linear-array ultrasound scanner with a 5-MHz transducer was evaluated for the study of follicular and luteal status in heifers. The ovaries of five heifers were monitored daily until all heifers were examined for a period from three days before an ovulation to three days after the next ovulation. There was a significant difference among days for diameter of the largest follicle and second largest follicle and for the number of follicles 4-6 mm and >10 mm. Differences seemed to be caused by the presence of several 4- to 6-mm follicles in early diestrus, growth to an ostensibly ovulatory size and subsequent regression of a follicle during mid-cycle, and selective accelerated growth of the ovulatory follicle four days before ovulation. The corpus luteum became visible approximately three days after ovulation and was identifiable throughout the rest of the interovulatory interval. In two of the five heifers, the corresponding corpus albicans was identified for three days after the second ovulation. Two heifers were induced to superovulate and follicular growth was monitored. The results indicated that the follicles which ovulated originated from the population present when the superovulation treatment was initiated. The ultrasound instrument was judged effective for monitoring and evaluating ovarian follicles and corpora lutea in normal and superovulated heifers.