User:Samsmith428/Estrous cycle

Lead
[my edits in bold]

The oestrous cycle or estrous cycle (derived from Latin oestrus "frenzy", originally from Greek οἶστρος oîstros "gadfly") is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous phases, otherwise known as 'rest' phases, or by pregnancies. Typically, estrous cycles repeat until death. These cycles are widely variable in duration and frequency depending on the species. Some animals may display bloody vaginal discharge, often mistaken for menstruation. Many mammals used in commercial agriculture, such as cattle and sheep, may have their estrous cycles artificially controlled with hormonal medications for optimum productivity. Naturally, estrous cycles are complimented by a rutting period of male counterparts within a species.

Cattle
Female cattle, also referred to as "heifers" in agriculture, will gradually enter standing estrus, or "standing heat," starting at puberty between 9 to 15 months of age. The cow estrous cycle typically lasts 21 days. Standing estrus is a visual cue which signifies sexual receptivity for mounting by male cattle. This behavior lasts anywhere between 8 to 30 hours at a time. Other behaviors of the female during standing estrus may change, including, but not limited to: nervousness, swollen vulva, or attempting to mount other animals. While visual and behavioral cues are helpful to the male cattle, estrous stages cannot be determined visually by the human eye. Rather, the stage can be estimated from the appearance of the corpora lutea or follicle composition.

Estrous Control
[see estrous synchronization]

Due to the widespread use of bovine animals in agriculture, cattle estrous cycles have been widely studied, and manipulated, in an effort to maximize profitability through reproductive management. Much estrous control in cattle is for the purpose of synchronization, a practice or set of practices most often used by cattle farmers to control the timing and duration of estrus in large herds.

There is variation between the available methods of cattle estrous synchronization. Treatment depends on herd size, specific goals for control, and budget. Some of the FDA-approved drugs and devices used to mimic natural hormones of the estrous cycle include, but are not limited to, the following classes:

There is variation between the available methods of cattle estrous synchronization. Treatment depends on herd size, specific goals for control, and budget.
 * Gonadorelin: There are currently five available gonadorelin products that are FDA-Approved. Usually, gonadorelin is used in conjunction with another estrous control drug (typically, prostaglandin). This drug is used to mimic gonadotropin releasing hormone (GnRH) and may also be used to treat ovarian cysts.
 * Prostaglandin: Mimics the prostaglandin F2-alpha hormone released when no pregnancy has occurred and regresses the corpus luteum. This drug is used to achieve more consistent results in artificial insemination. Typ
 * Progestin: Used to suppress estrus and/or block ovulation . Most commonly, it is administered via an intravaginal insert comparable to an IUD, which used in controlling menstrual periods. It is also available as a medicated feed, but this method is not yet approved for cattle crop synchronization.

While estrous management is deemed safe by the FDA and may provide added monetary gain, repeated cycles of gestation and constant lactation causes dairy cattle to exhaust their bodies leaving them with a shortened lifespan of approximately 4 years. In comparison, the average captive lifespan ranges from 15-20 years. Bovine estrous cycles may also be impacted by other bodily functions such as oxytocin levels. Additionally, heat stress has been linked to impairment of follicular development, especially impactful to the first-wave dominant follicle. Future synchronization programs are planning to focus on the impact of heat stress on fertilization and embryonic death rates after artificial insemination.

Additionally, work has been done regarding other mammalian females, such as in dogs, for estrous control; However, there are yet to be any approved medications outside of those commercially available.