1. A cow's estrus cycle averages 21 days. 母牛的发情周期平均为21天。
2. Estrus: During this period, which also lasts approximately nine days, the female will accept the male and is fertile. 发情期：这段时期，同样持续约九天，母犬可以和公犬进行交配并受孕。
3. If a dog to own the estrus period for the election of her husband masters, the eyes of a certain good, not anxious to lock. 如果自家的一条母獒到了发情期，主人为其选夫婿，看中某条好公獒，先别着急锁定。
英英解释
n.
1. applies to nonhuman mammals: a state or period of heightened sexual arousal and activity
