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Reproductive Ultrasonography for Monitoring Ovarian Structure Development, Fetal Development, Embryo Survival, and Twins in Beef Cows

Lamb, G.C., Dahlen, C.R., Brown, D.R.
The Professional animal scientists 2003 v.19 no.2 pp. 135-143
Internet, abnormal development, beef cows, business enterprises, corpus luteum, embryonic mortality, estrous cycle, fetal development, fetus, gonadotropin-releasing hormone, image analysis, insemination, monitoring, oocytes, ovarian follicles, pregnancy rate, reproductive efficiency, sex determination, sex determination analysis, technicians, twins, ultrasonography, uterus
The area that has arguably benefited more from the development of ultrasound technology than any other area is reproduction in large animals. Ultrasonography is now commonly used for fetal sexing and early embryonic detection. Ultrasound offers researchers the ability to visually characterize the uterus, fetus, ovary, corpus luteum (CL), and follicles and has been used to monitor the growth and atresia of individual antral follicles, which usually takes place in two or three waves during the estrous cycle. We recently determined by ultrasonography that the diameter of the ovulatory follicles prior to the second injection of gonadotropin-releasing hormone (GnRH) in a CO-Synch estrous synchronization system was related to overall pregnancy rates (PR). Cows that had follicles >12 mm had greater (P<0.01) PR than those with follicles =12 mm. In addition, cows that had follicles from 16.0 to 17.9 mm had the greatest (P<0.01) PR. With ultrasonography, the incidence of embryonic loss in beef cows from d 25 to 45 of gestation was 6.5%, whereas, a 4.2% incidence of embryonic loss was detected in beef heifers where ultrasonography was performed at d 30 of gestation and subsequently palpated rectally between d 60 and 90 after insemination. Ultrasonography was successful in identifying twins in induced twinning studies in which it was determined that cows induced to develop twins (67%) had more (P<0.05) fetuses as a percentage of all treated cows than those inseminated artificially (48%) or receiving an embryo (32%). In addition, the point of greatest embryonic loss occurs from d 33 to 69 in cows pregnant with multiple fetuses. Fetal sexing is fast becoming a common management tool in beef cattle enterprises with accuracy in sex determination exceeding 97%. The applications of ultrasound used by scientists include the ability to monitor follicular characteristics, to monitor ovarian function, and the ability to aid in follicular aspirations and oocyte retrieval. In the future, as technology improves, technicians will have an opportunity to use the internet or video conferencing for ultrasound image analyses. With every new technological development, scientists, veterinarians, and producers discover new possibilities for the use of reproductive ultrasound to enhance the scientific merit of research or improve reproductive efficiency in livestock.