Estrous cycle in domestic animals

An estrous cycle is a period of time in a female, between two subsequent heats or estrus. They occur during her reproductive cyclicity, after reaching puberty. Females are receptive to copulation with males and are able to facilitate the transport of spermatozoa through the uterus only during heat. At this moment, their reproductive system is in optimal environmental conditions, close to ovulation and able to become pregnant. Estrous cycles vary between species; there are some differences according to the moment in which non pregnant females present heats or anestrus (period of time of reproductive quiescence during which femalesdo not display estrus). In relation to this, females are classified as:
 * Polyestrous continuous, such as cows and sows, present heats between regular periods of time during all the year. They can become pregnant without regard to the season of the year.


 * Seasonally polyestrous, including mares, queens, ewes and nanny-goats, present several heats during their reproductive season and remain in anestrus during their non-reproductive season. They are classified as “short day breeders” when they present estrous cycles during autumn when day length is decreasing (goats and ewes) and “long day breeders” (mares and queens) when they show estrous mainly during spring, when day length increases.


 * Monoestrus, such as bitches, show one or at the most two heats per year. If they do not become pregnant after the heat, they present a long luteal phase and then remain in anestrous until the following year.

The length of the estrous cycle and the duration of the heat also vary between species (Table 1). Ovulations occur in most domestic species during the last third part of the heat. Exceptions are cows, which ovulate around 12 hours after finishing sexual receptivity, and queens, which are induced ovulators.

quiz
{An estrous cycle is a period of time in a female, between two subsequent ________ or estrus. - heats - pregnancies - ovulations - menses
 * type="[]"}
 * Correct! The estrous cycle is the period between two subsequent heats.
 * Incorrect. The estrous cycle is not defined by pregnancies.
 * Incorrect. The estrous cycle is defined by heats, not ovulations.
 * Incorrect. Menses is related to the menstrual cycle in primates, not the estrous cycle in other animals.

{Females are receptive to copulation with males and are able to facilitate the transport of spermatozoa through the uterus only during ________. - pregnancy - ovulation + heat - menstruation
 * type="[]"}
 * Incorrect. Females are receptive during heat, not pregnancy.
 * Incorrect. While ovulation is a part of the cycle, the correct term is heat.
 * Correct! Females are receptive to copulation during heat.
 * Incorrect. Menstruation is related to the menstrual cycle in primates, not the estrous cycle in other animals.

{Polyestrous continuous animals, such as cows and sows, can become pregnant ________. - only during a specific season + without regard to the season of the year - only during heat - only after ovulation
 * type="[]"}
 * Incorrect. Polyestrous continuous animals can become pregnant throughout the year.
 * Correct! They can become pregnant at any time of the year.
 * Incorrect. While they are most receptive during heat, the defining characteristic of polyestrous continuous animals is that they can become pregnant throughout the year.
 * Incorrect. While ovulation is necessary for pregnancy, the defining characteristic is their ability to become pregnant any time of the year.

{Seasonally polyestrous animals, like mares and queens, are classified as “long day breeders” when they show estrous mainly during ________. - winter - autumn + spring - summer
 * type="[]"}
 * Incorrect. Long day breeders show estrous during increasing day lengths.
 * Incorrect. This is when short day breeders show estrous.
 * Correct! Long day breeders like mares and queens show estrous mainly during spring.
 * Incorrect. The defining characteristic of long day breeders is that they show estrous during spring when day length increases.

{Monoestrus animals, such as bitches, show ________ heats per year. - multiple + one or at the most two - three to four - continuous
 * type="[]"}
 * Incorrect. Monoestrus animals have a limited number of heats per year.
 * Correct! Bitches, which are monoestrus, show one or at most two heats per year.
 * Incorrect. This is more than the typical number for monoestrus animals.
 * Incorrect. Monoestrus animals do not have continuous heats.