When the Graysing Cattle Company needs to diagnose pregnancies in their cows and determine the fetal sex of the unborn calves, they call on the Livestock Herd Health and Reproduction Service from the UC Davis Veterinary Medical Teaching Hospital. Their small operation (about 20 head) raises beef cattle, specifically club calves, and has used the Service for more than ten years.
Fetal sex determination offers Graysing valuable information that can be used for herd management. By knowing whether the calf will be male or female, especially in smaller herds, they can plan for the next year of replacement animals and animals to be sold. Graysing likes to balance growing the herd and selling steer calves to 4H and FFA students for livestock projects, and this technique allows marketing of those calves even before they are born. Many of Graysing’s cattle have gone on to win awards at county fairs throughout California.
Using transrectal ultrasound (performed by UC Davis veterinarians with a portable unit at the client’s ranch), the pregnant uterus and fetus can be identified. The livestock veterinarians look for the genital tubercle, a structure that will go on to become the external genitalia of the calf. Based on the location of the genital tubercle (near the tail for females and near the umbilical cord for males), they are able to determine the sex. The optimum window for determining fetal sex in a cow is 58 to 70 days, as this is when the genital tubercle can easily be identified. Before 58 days, the fetus has not formed enough to determine sex, and after 70 days, the fetus has usually grown too much and moved to an unidentifiable position in the uterus. While this is a narrow time frame, it can reliably be used in cows with a known breeding date, such as those that were artificially inseminated.
During their latest visit to Graysing, the Service checked four cows for pregnancies. Only three of the four showed fetuses growing – in cows Sonja, Mally and Catalina (named after UC Davis veterinarian Dr. Catalina Cabrera). Ultrasound images showed that all three were pregnant with females.
On visits to Graysing and other ranches throughout Northern California, residents and students training with the Livestock Herd Health and Reproduction Service gain valuable hands-on experience in many aspects of livestock reproduction, including advanced techniques such as this fetal sexing. Reproductive ultrasound is a widely used imaging technique in livestock medicine, so it is important that the school’s veterinary students graduate being skilled in transrectal ultrasonography. It is equally important to have clients like Graysing who are supportive of the school’s clinical teaching programs. Their utilization of the hospital’s livestock services plays an integral role in the training of future veterinarians.