estrus

The female dog is in estrus and attracts male dogs.

用法提示：此处estrus为不可数名词，表示发情状态。

Researchers noted that the onset of estrus in the herd occurred earlier this year.

用法提示：estrus作为不可数名词，指发情期这一时间段。

Farmers track estrus cycles to optimize breeding times.

用法提示：estrus用作定语修饰cycles，仍表示发情。