On average, the gestation period or length-of-pregnancy of a cow is 285 days long. This is similar to the pregnancy period of a woman, which is closer to around 9 months or ~260 days.However, actual gestation period of a cow can range from 270 days to 295 days, depending primarily on breed[s], age, body condition and nutritional health.Gestation period is also controlled by genetics, but not rate of maturity.owever, actual gestation period of a cow can range from 270 days to 295 days, depending primarily on breed[s], age, body condition and nutritional health.