Ultrasound has been utilized as a tool in beef and dairy research systems since the early 1980s (Perry and Cushman 2016), and in more recent years has become available to commercial livestock agriculture. An ultrasound is an electronic instrument that sends out ultrasonic sound waves from an attached device called a transducer. The waves pass freely through fluid and are reflected back to the probe once they contact a soft tissue like muscle or a dense structure like bone, resulting in an image that can be identified as the placenta, fetus, or other organs. In addition, ultrasound may also be utilized to determine subcutaneous body fat content on finishing cattle (Hicks 2014), and it is also an important diagnostic tool for veterinary medicine. Although ultrasound technology may be used for various functions, this article will focus only on using ultrasound to assist with beef cattle reproduction, which includes the diagnosis of pregnancy status, and the age and sex of a fetus.
Ultrasound is a rapid method for pregnancy diagnosis, and experienced palpators can adapt to ultrasound quickly, with a relatively small increase in the time required to assess pregnancy compared to rectal palpation (11.3 seconds using palpation per rectum versus 16.1 seconds using ultrasound) (Galland et al. 1994; Fricke and Lamb 2002). Although ultrasound after 45 days of gestation did not increase accuracy of pregnancy diagnosis for an experienced palpator, it may improve diagnostic accuracy of less experienced palpators (Galland et al. 1994; Fricke and Lamb 2002). Additionally, ultrasound can accurately determine the presence of a viable embryo as early as 30 days after mating. The accuracy of detecting fetal viability may approach 100% because the user can visually identify the viable embryo by the presence of a beating heart.
A technician with a trained eye has the capability of accurately assessing the age of the fetus based on fetal size (Figure 1). To determine fetal age, the technician uses developmental characteristics of the fetus, such as forelimb buds, hind limb buds, fetal movement, and ribs (Table 1; Curran et al. 1986), or specific fetal measurements such as crown-rump length (Table 2; Hughes and Davies 1989). When the fetus reaches 60–85 days of age, the trained user can even determine fetal sex by the absence and/or presence of the fetal genitalia with over 95% accuracy (Figure 2). If imaging for embryo sexing is done after 60-85 days of age, then the fetus will increase in size, making the manipulation of the transducer more difficult to obtain the desired image. Also, as the gravid uterus enlarges and descends over the pelvic rim into the body cavity, fetal sexing is virtually impossible without retracting the gravid horn (Fricke and Lamb 2002).
Identification of early embryo development characteristics by transrectal ultrasonography (Adapted from Curran et al. 1986; Perry and Cushman 2016).
Identification of fetal age by crown-rump length (Adapted from Curran et al. 1986; Perry and Cushman 2016).
Most producers are faced with difficult decisions when choosing bulls that address the contributions of both maternal and carcass traits. Not only is there variation in the attributes of multiple breeds, but variation within a breed is substantial. By combining ultrasound and AI (artificial insemination), a producer can develop a breeding program that optimizes both maternal and carcass traits. Prior to the start of a normal breeding season (or during the first 21–30 days of the breeding season) bulls possessing high maternal traits may be selected and used in an AI system. After this time, natural service bulls, selected for carcass merit, can be used for the remainder of the breeding season. Using ultrasound, the producer may now determine which females are pregnant with AI-sired heifer calves based on the age and sex of the fetus. These females can be managed separately with the knowledge that they are pregnant with heifer calves possessing quality maternal traits that have the potential to be replacement heifers. Further, because these heifer calves were conceived early in the breeding season, they will be older and larger and have the possibility of being more productive replacements when bred as yearlings in the upcoming breeding season. Calves from all other females will either be male siblings to the replacement heifers or progeny of the terminal cross (carcass trait) bulls.
Many producers may wish to use a common bull type but manage individual pregnancies depending on the sex of the calf. An example of this management strategy is found in purebred operations wishing to separate cows giving birth to bull calves from those giving birth to heifers. At approximately 60–85 days after breeding, ultrasound may be used to determine fetal sex. Also, cows that did not conceive will be identified. Producers can now divide the herd and manage each of the births in a manner that best fits their production system for heifer and bull calves.
In a typical commercial cow-calf production environment a controlled breeding season can range from 60 to 120 days. Therefore, on a common weaning day, calves from these cows vary substantially in both age and weight. By using ultrasound, as early as 30 days after the conclusion of the breeding season, producers can divide their herd into three groups: 1) cows that became pregnant early in the breeding season, 2) cows that became pregnant late in the breeding season, and 3) open cows. Each of these groups may now be managed to best complement their pregnancy status. For instance, late-pregnant cows may be maintained on pastures that will optimize calf growth, alleviating differences in calf weaning weight between older siblings. Producers may wish to utilize creep feeding for calves born to cows in the late-pregnant group, or supplement these cows in a manner that might lessen the following postpartum interval. Finally, producers may wish to wean these groups on different dates, optimizing calf uniformity and market price.
Specifically in FL there are additional common practical uses of reproductive ultrasound technology:
One example is the use of ultrasound for yearling heifers 30 days after the end of the breeding season to accurately (95%–100%) determine pregnancy status compared to rectal palpation, which takes between 50 and 60 days to gain the same accuracy. Thus, producers are able to make immediate culling decisions on heifers and do not need to keep them on grass or feed them for another 20–30 days, which reduces the feed cost significantly.
For large groups of yearling heifers, ultrasonography may assist in culling heifers based on fetal size. Only the heifers that become pregnant in the first 60 days of a 90-day breeding season will be retained. The remaining late pregnant heifers will be sold and not kept in the cow herd. This allows producers to sell pregnant heifers that are worth more than open heifers.
For commercial producers that use AI programs, ultrasound may be used at 50–60 days after AI to identify which cows are pregnant to the AI compared to natural service. In production systems that utilize timed AI programs, ultrasound can be performed as early as 30 days after AI, allowing producers to make management and strategic reproductive decisions during the breeding season. Identifying those cows pregnant to AI (by notching ear tags or inserting an additional ear tag) allows producers to sort cows into calving groups the following spring based on whether they were pregnant to AI or not. Just as important, ultrasound allows producers to identify the cows that were not pregnant at the end of the breeding season and can be culled earlier, which reduces feeding cost and increases profitability.
First-calf heifers are more prone to dystocia (calving problems). By identifying breeding dates, approximate calving dates can be determined, allowing increased observations during the calving of first-calf heifers to help reduce the incidence of calf loss from calving difficulties.
There are other potential uses for ultrasound in cow-calf production systems. Two limitations in Florida are the availability of trained technicians and the costs associated with its use. In addition, the expansive nature of the Florida beef production systems generally does not afford cattlemen access to the cows when ultrasound may be most effective. Nonetheless, transrectal ultrasonography has and will continue to have a role in the successful reproductive management of cattle herds (Perry and Cushman 2016). As with any emerging technology, these hurdles will be overcome as producers find ways to incorporate ultrasound into reproductive management practices. Contact your local UF/IFAS Extension agriculture agent for the availability of a trained ultrasound technician in your area.
Curran, S., R. A. Pierson, and O. J. Ginther. 1986. "Ultrasonographic appearance of the bovine conceptus from days 20 through 60." J. Am. Vet. Med. Assoc. 189:1295–1302.
Fricke, P. M., and G. C. Lamb. 2002. "Practical applications of ultrasound for reproductive management of beef and dairy cattle." In: The Applied Reproducive Strategies in Beef Cattle Workshop. Sep. 5–6, 2002, Manhattan, Kansas.
Hicks, C. 2014. "Using Live Animal Carcass Ultrasound in Beef Cattle". University of Georgia Extension. Bulltein 1337. Available at: https://secure.caes.uga.edu/extension/publications/files/pdf/B%201337_3.PDF
Hughes, E. A., and D. A. Davies. 1989. "Practical uses of ultrasound in early pregnancy in cattle." Vet. Rec. 124:456–458.
Lamb, G.C. 2001. "Reproductive Real-Time Ultrasound Technology: An Application for Improving Calf Crop in Cattle Operations." In Factors Affecting Calf Crop: Biotechnology of Reproduction, edited by M.J. Fields, 231–153. Boca Raton, FL: CRC Press.
Perry, G. A., and R. A. Cushman. 2016. "Invited Review: Use of ultrasonography to make reproductive management decisions." Prof. Anim. Sci. 32:154–161.