What is the Difference Between Estrous and Menstrual Cycle?
🆚 Go to Comparative Table 🆚The estrous and menstrual cycles are two types of reproductive cycles that occur in female mammals. They exhibit cyclic ovarian functions and are driven by reproductive hormones. The main differences between the estrous and menstrual cycles are:
- Occurrence: Estrous cycles occur in non-primate mammals (e.g., cows, sheep, horses, rabbits, and pigs), while menstrual cycles occur in primates (e.g., humans, apes, and monkeys).
- Endometrium: During the estrous cycle, the endometrium is reabsorbed if conception does not occur, while in the menstrual cycle, the endometrium is shed through menstruation.
- Sexual Activity: Females of species with estrous cycles are generally only sexually active during the estrus phase of their cycle, also referred to as being "in heat". In contrast, females of primates are sexually active at any time of the menstrual cycle.
- Cycle Variability: Estrous cycle variability differs among species, and cycles are typically more frequent in smaller animals. Menstrual cycles, on the other hand, tend to have a more consistent frequency and duration within a species.
In summary, the estrous cycle is characteristic of non-primate mammals, reabsorbs the endometrium, and is associated with sexual activity only during the estrus phase. In contrast, the menstrual cycle occurs in primates, sheds the endometrium, and allows for sexual activity throughout the cycle.
Comparative Table: Estrous vs Menstrual Cycle
The estrous and menstrual cycles are both reproductive phases in mammals, but they have some differences. Here is a comparison between the two:
| Feature | Estrous Cycle | Menstrual Cycle |
|---|---|---|
| Occurs in | Non-primate mammalian females (e.g., dogs, cows, sheep, deer, horses, tigers) | Primate females (monkeys, apes, and humans) |
| Sexual activity | Females are sexually active during the estrus phase of the cycle or termed as "in heat" | Females are sexually active throughout the cycle |
| Endometrium | Endometrium is reabsorbed | Endometrium is shed in each cycle |
| Hormonal control | Controlled by hormones such as follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogens, and progesterone | Controlled by hormones such as FSH, LH, estrogens, and progesterone |
| Cycle length | Varies among species, ranging from 18 to 24 days in some examples | Varies among individuals, typically lasting between 21 and 35 days |
| Ovulation | Ovulation occurs 1-2 days before the end of estrus in some species (e.g., cows, sheep, goats) | Ovulation typically occurs in the middle of the menstrual cycle |
| Fertility | Fertility is determined by the presence of a suitable follicle in some species (e.g., alpacas) | Fertility is determined by the timing of ovulation and the lifespan of sperm |
In summary, the estrous cycle occurs in non-primate mammals and is characterized by a reabsorbed endometrium, sexual activity limited to the estrus phase, and varying cycle lengths based on species. The menstrual cycle occurs in primates and is characterized by a shed endometrium, sexual activity throughout the cycle, and slightly shorter cycle lengths. Both cycles are controlled by hormones and involve ovulation.
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