Healthful Herd: Basic Hormones

Using biology to your benefit

Healthful Herd: Basic Hormones

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Hormones are biology’s “chemical messengers” that signal and initiate certain functions. They work in minimal concentrations and are powerful enough to regulate everything from kidding to mating behaviors to the “fight or flight” reflex.

These chemicals are at play in our goats all the time. And, depending on the situation, people can also provide them artificially for the desired response. And while endocrinology is a field of study that encompasses far more details than what the backyard goatherd needs to know, understanding the basics of how hormones function helps understand life processes.

What are hormones, anyway?

Each hormone in a body can act at a certain time to signal the body’s desired response. These can be delivered naturally (from the brain, glands, bloodstream, or organs depending on the type) or artificially via injection.

For example, giving oxytocin to stimulate milk letdown and contractions or different reproductive hormones is common to induce or halt a heat cycle.

There are many hormone types and compositions classified into three major groups: peptides, steroids, or amines. Some target multiple organs or cells at different sites throughout the body by reaching them at a “receptor” point to trigger the needed response. How many and where these receptors are on certain target cells can change upon certain conditions.

Estrogen levels, for instance, will increase in bodily circulation shortly before a doe kids. This circumstance helps stimulate the increase of oxytocin (another hormone) receptors on the cells that make up the uterus.  As these receptors reach their respective cells, oxytocin is released and telling them to contract for the kidding process involuntarily.

Hormones at work

Anyone who has worked with heat synchronization or timed-A.I. on their does already has a basic understanding of artificial hormone treatment to receive the desired response. Often, a series of shots deliver the same reproductive hormones — Gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH).

In an ordinary circumstance, the brain’s hypothalamus secretes GnRH, which then acts on the pituitary gland that releases both FSH and LH. FSH then stimulates increased estrogen production to promote the growth of a follicle on the ovary. (In a growing doe, estrogen triggers mammary gland development and other secondary sexual characteristics.) While this is happening, the estrogen is at work to start the external signs of estrus behavior.

Outside factors and environments can also influence hormones. One of the lesser-common ways to induce heat is light exposure.

LH is responsible for ovulation and the development of the corpus luteum, an ovarian structure after ovulation that secrets the hormones needed to sustain a pregnancy after conception.

When a pregnancy doesn’t occur after the window opens, the uterus naturally secretes the hormone prostaglandin 2-alpha (PGF2α) to kill off the CL and ultimately restart the cycle.

As you can see from this process, it’s relatively simple to manipulate the cycle with injections artificially. There are several methodologies and products to do this, depending on the program used. They can induce heat at the time desired by the breeder.

Outside factors and environments can also influence hormones. One of the lesser-common ways to induce heat is light exposure. Both the hypothalamus and pituitary gland (known as the hypothalamic-pituitary-gonadal axis) naturally respond to the shortening of daylight to trigger estrous.

In this sense, they function as a single endocrine gland since they are working together to form the response. Research has shown that limiting artificial lighting hours to the same amount that an animal will experience in the goat breeding season can trigger their heat cycles. You can use this in tandem with shot protocols as well.

The other common hormone treatment is when it comes to milk production or even helping with smooth muscle contractions in the uterus. Providing oxytocin as recommended by a vet can assist with uterine contractions around kidding and then with milk let down. Some herds successfully treat difficult milkers with milk down issues by injecting a tiny amount of oxytocin directly into the milk vein at milking time.

This is one example of how understanding how hormones naturally work can empower goatherders to better work with their vets and handle issues from a biological standpoint.

SOURCES

  • Goats. (2019, August 14). Reproductive Biology Goat Reproductive Physiology. Goats. Retrieved October 11, 2021, from goats.extension.org/reproductive-biology-goat-reproductive-physiology/. 
  • Romano, J. E. (2021, April). Hormonal control of estrus in goats and sheep – management and Nutrition. Merck Veterinary Manual. Retrieved October 11, 2021, from merckvetmanual.com/management-and-nutrition/hormonal-control-of-estrus/hormonal-control-of-estrus-in-goats-and-sheep. 
  • drugs.com/vet/oxytocin-injection.html
  • Frandson, R. D., Wilke, W. L., & Fails, A. D. (2009). Endocrinology. In Anatomy and physiology of Farm Animals (pp. 207–222). essay, Wiley Blackwell.

Originally published in the January/February 2022 issue of Goat Journal and regularly vetted for accuracy.

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