Which Of The Following Hormones Are High During Estrus In Horses?

**Which hormones are high during estrus in horses?**

During estrus, also known as the heat cycle, in horses, there are several hormones that play a crucial role in the reproductive process. These hormones are responsible for initiating and regulating the various physiological changes that occur in a mare’s reproductive system. Understanding the hormonal changes that occur during estrus is essential for horse owners, breeders, and veterinarians alike. Let’s take a closer look at the hormones that are elevated during this period.


One of the primary hormones involved in the equine estrus cycle is progesterone. Progesterone is produced by the corpus luteum, which forms on the ovary after ovulation. During estrus, progesterone levels decrease significantly as the corpus luteum regresses and prepares for the next cycle. This drop in progesterone triggers a cascade of hormonal changes that lead to estrus.

Follicle-Stimulating Hormone (FSH)

As progesterone levels decline, the pituitary gland releases follicle-stimulating hormone (FSH). FSH is responsible for stimulating the development and maturation of follicles within the ovaries. These follicles contain the eggs, or oocytes, that will eventually be released during ovulation. The increase in FSH levels during estrus promotes the growth of dominant follicles in preparation for ovulation.


Estrogen is another hormone that is high during estrus in horses. It is primarily produced by the developing follicles within the ovaries. As the follicles mature and increase in size, they release increasing amounts of estrogen into the bloodstream. Estrogen plays a crucial role in preparing the mare’s reproductive tract for breeding. It helps to thin the cervical mucus and increase blood flow to the uterus, making it more conducive to fertilization.

Luteinizing Hormone (LH)

Luteinizing hormone (LH) is a key hormone involved in the final stages of the estrus cycle. Just before ovulation, LH levels surge, triggering the release of the mature oocyte from the dominant follicle. This surge in LH is often referred to as the “LH peak.” It is this peak that signals the optimal time for breeding or artificial insemination in horses.

Prostaglandin F2-alpha (PGF2α)

While not a hormone itself, prostaglandin F2-alpha (PGF2α) is a lipid compound that plays a crucial role in the estrus cycle of horses. PGF2α is responsible for initiating the regression of the corpus luteum, leading to the decline in progesterone levels. This decline is necessary for the cycle to begin again. PGF2α is primarily released from the lining of the uterus during estrus and is involved in the coordination of follicular growth and ovulation.

Gonadotropin-Releasing Hormone (GnRH)

Gonadotropin-releasing hormone (GnRH) is a hormone released by the hypothalamus in the brain. GnRH stimulates the release of both FSH and LH from the pituitary gland. It acts as a “master regulator” of the reproductive system, coordinating the timing and release of other hormones involved in the estrus cycle. GnRH levels fluctuate throughout the cycle, reaching their highest point just before the LH surge and ovulation.

Frequently Asked Questions

Q: How long does estrus last in horses?

The duration of estrus in horses can vary between individuals, but on average, it lasts around 5 to 7 days. However, it’s important to note that the entire estrus cycle, from the beginning of one heat to the beginning of the next, typically lasts around 21 days.

Q: Can I predict when my mare will be in estrus?

Yes, it is often possible to predict when a mare will be in estrus by closely monitoring her behavior and physical signs. Common signs of estrus include frequent urination, winking of the vulva, and a generally more receptive and easy-going attitude. Additionally, veterinarians can perform hormonal assays to measure the levels of specific hormones in the mare’s bloodstream, providing more accurate information about her reproductive status.

Q: Can I improve my chances of successful breeding by timing it with the hormone peaks?

Timing breeding with the hormone peaks, particularly the LH surge, can significantly improve the chances of successful fertilization. By breeding within 24 hours of the LH surge, the mare is more likely to release a mature oocyte, increasing the chances of conception. Working closely with a veterinarian experienced in equine reproduction can help determine the best timing for breeding based on hormone levels and other factors.

Final Thoughts

Understanding the hormonal changes that occur during estrus in horses is vital for successful breeding and reproductive management. By recognizing the role of progesterone, FSH, estrogen, LH, PGF2α, and GnRH, horse owners and breeders can better time breeding, monitor reproductive health, and optimize fertility. Working closely with a veterinarian can provide valuable insights into the mare’s estrus cycle and help ensure the best possible reproductive outcomes.

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