来自PIE*eis, 发情，激情，词源同ire. 可能来自PIE*aidh, 燃烧，词源同edifice, ether.

1. The next estrus was delayed.

下一次发情推迟了.

2. A cow's estrus cycle averages 21 days.

母牛的发情周期平均为21天.

3. Anestrus ( absence of estrus ) is not a disease but a sign of a variety of conditions.

乏情不是一种疾病,而是一种多方面的体态迹象.

4. In cows and many other animals, the female is in estrus just before ovulation.

母牛和许多其他的雌性动物都正好是在排卵前发情.

5. During estrus, the female is fertile and will accept a male.

在发情期, 母犬可以接受交配并且具有生育能力.