A female mammal, excluding higher primates, is in heat (also known as estrus) during the period of her sexual cycle when she is receptive to mating and able to conceive.
Understanding Estrus
Estrus, or being "in heat," is a recurring phase in the reproductive cycle of most female mammals. It's characterized by specific physiological and behavioral changes that signal readiness for mating.
Key Characteristics of Estrus:
- Receptivity to Mating: The female actively seeks out or accepts advances from males.
- Ovulation: The release of an egg (or eggs) from the ovaries, making fertilization possible.
- Hormonal Changes: Increased levels of estrogen trigger behavioral changes and prepare the reproductive tract for pregnancy.
- Physical Signs: Depending on the species, there may be visible signs like swelling or discharge in the vulvar area, or changes in scent.
Estrus vs. Menstrual Cycle
It's important to distinguish estrus from the menstrual cycle, which is characteristic of humans and other higher primates. In the menstrual cycle, the uterine lining is shed if fertilization does not occur, whereas in estrus, the uterine lining is reabsorbed.
Estrus Cycle Variation
The frequency and duration of estrus cycles vary greatly among species. Some animals are polyestrous (having multiple estrus cycles during a breeding season), while others are seasonally monoestrous (having only one estrus cycle per breeding season). Examples include:
- Dogs: Typically have one or two estrus cycles per year.
- Cats: Are seasonally polyestrous and cycle repeatedly during the breeding season.
- Cows: Cycle approximately every 21 days.
Conclusion
Essentially, a female mammal (excluding higher primates) is "in heat" when she's in the estrus stage of her reproductive cycle, making her receptive to mating and capable of becoming pregnant.
