Estrus (also spelled œstrus) or heat in female placental mammals eutherians is the period of greatest female sexual responsiveness usually coinciding with ovulation. Most female placental mammals will only seek sex during their heat.

Human females may seek sex throughout their heat cycles but do experience periods of greater sexual responsiveness (as well as other emotional and behavioral changes at the peak of heat cycles).

The period of estrus in the female is preceded by an increase in estrogen (also spelled œstrogen). Evidence of the animal being in heat is signalled by leakage of blood from the vagina, or other changes in secretions and urinary habits. A signal trait of estrus is the lordosis reflex in which the animal spontaneously elevates their hindquarters.

A similar term, estrous, refers to the entire fertility cycle.

The phases of the estrous cycle are proestrus, estrous, metestrus, and diestrus. Anestrus refers to a state where the normal cycle stops.

The receptive behavior of the estrus female is the basis of husbandry and the breeding of placental mammals such as cows, sheep, dogs, cats, etc..

Frequency of female estrous cycles in several mammals:

• Cow - 21 days
• Elephant - 16 weeks
• Goat - 21 days
• Rodents - 4–6 days
• Human - 28 days

Etymology

The Latin oestrus, meaning frenzy, or gadfly. This in turn comes from the Greek oistros, which has the same meaning.

This etymology reflects the intense drive, by the female in heat, for coitus.

See also

• mating system
• endometrium
• fertility
• reproductive cycle

External links

• Information on the estrous cycle