When a female calf is born as a twin to a male calf, a sterile female known as a

When a female calf is born as a twin to a male calf, a sterile female is known as a Free martin (neuter).
A freemartin is a bull and heifer combination of calves carried at the same time. The male hormones in the uterus of the pregnant cow prevent the heifer's reproductive tract from forming.
Development of the reproductive tract is compromised in about 95% of female calves born co-twin to a male. Affected calves are called “freemartins”.