Anestrus is a phase in the reproductive cycle of female mammals, including dogs, cats, and cattle, where the animal is not in heat and does not exhibit signs of estrus. This period can vary in length depending on the species and individual health, typically lasting several months. During anestrus, the ovaries are inactive, and there is no production of eggs. This phase is essential for allowing the reproductive system to rest and recover between breeding cycles. Anestrus helps ensure that when the animal does enter the next estrus phase, it is healthy and capable of conceiving.