Final answer:
A beef calf requires the cow to be bred around 82 days post-partum to allow for the cow's recovery and to fit within the annual cycle considering the 280-day gestation period for cattle.
Step-by-step explanation:
To ensure a beef calf is born each year, a cow needs to be bred around 82 days post-partum, commonly known as the voluntary waiting period. This allows for the cow's reproductive system to recover and for the cow to be in a good condition to conceive again. The estrous cycle of cows is approximately 21 days, and breeding should occur during the estrus period when the cow is most fertile.
The gestation period for cows is approximately 280 days (9 months). Therefore, if you want the cow to give birth to one calf per year, she would need to become pregnant again roughly three months after giving birth to allow for the full gestational period plus the recommended post-partum recovery time.