Reproductive performance in mares subjected to examination by diagnostic ultrasound

Mares were subjected to frequent examination by diagnostic ultrasound and data were compiled with respect to reproductive efficiency. The data were collected over a 3-yr period on 1032 light horse mares. The cummulative pregnancy rate at 35 d post-ovulation was 96.8% and the pregnancy rate per cycle was 76.0% as determined by ultrasound examination. The average number of cycles per conception was 1.43, with an average of 2.29 inseminations per cycle. The incidence of early embryonic death was 7.8%. Mares were subjected to an average of 5.04 scans during the follicular phase of the cycle. The average number of ultrasound examinations per mare (including pregnancy examinations) was 9.99. Although these data were obtained from an experiment that did not use both control and treated mares, there was no indication that preovulatory oocytes or embryos were damaged by routine ultrasound examination. Comparisons with existing data from commercial facilities are difficult to make concerning any improvement in reproductive efficiency resulting from the routine use of ultrasonography, but these data do suggest relative safety in equine reproductive management when ultrasound examinations are conscientiously used.