estrus

The female dog is in estrus and attracts male dogs.

母狗正处于发情期，吸引公狗。

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

研究人员注意到今年牛群发情期开始得更早。

Farmers track estrus cycles to optimize breeding times.

农民追踪发情周期以优化配种时机。