Final answer:
A freemartin is the term given to a sterile heifer born with a twin bull. It occurs in cattle and is caused by the close proximity of the male and female embryos during development.
Step-by-step explanation:
The term given to a sterile heifer born with a twin bull is called a freemartin. A freemartin is a female calf that is born as a twin with a male calf, and due to the exchange of hormones in the uterus, the female calf becomes sterile. This phenomenon occurs in cattle and is caused by the close proximity of the male and female embryos during development.