A child born to a married woman is presumed under common law to be the child of her husband by a presumption of paternity or presumption of legitimacy.
The behaviour of cows and heifers after they have conceived is one of the best non-invasive means of determining pregnancy in cattle. Simply put, pregnant cattle will not (or should not) come into estrus or heat for the entire duration of the 9.34-month (285 day) gestation period.
Like I covered above, once a cow gives birth to her calf she is no longer pregnant. She is producing milk instinctively to nourish her newborn calf. This happens all the time with beef cows and their calves, which stay together for 6 to 8 months until the calf is large and independent enough to be weaned.