Veterinary Medicine Extension

University of California, Davis

Tulare, CA 93274

June 25, 1999

A variety of hormones are being used on dairies to treated reproductive disorders and to regulate the estrous cycle for timed breeding. These hormones act directly on the reproductive organs in some cases and in other instances they act on the pituita ry gland to stimulate the release of naturally occurring hormones, which in turn act on the reproductive organs. Prostaglandin (PFG), estrogen and oxytocin act directly on the reproductive organs whereas gonadotrophic releasing hormone (GnRH) acts at the level of the pituitary gland. The purpose of this article is describe the more common hormones and their target organs as well as to focus on their intended action and practical applications on the dairy.

The more common reproductive hormones are PFG, human chroionic gonadotropin (HCG), gondadotropic releasing hormone (GnRH), estrogen, oxytocin, progesterone, lutenizing hormone (LH) and follicular stimulating hormone (FSH). All of these are available o ver the counter or through the veterinarian who works with the dairy reproductive herd health program. All of these hormones are administered by injection to dairy cows.

GnRH causes the pituitary gland to secrete both LH and FSH. These two naturally occurring hormones, in concert with other changing levels of hormones, cause the ovulation of the dominate follicle present on the ovary (Figure 1). GnRH can be use d to treat cows with cystic ovarian disease or cystic ovaries and also is used in some estrous synchronization programs. Injections of GnRH help to synchronize the follicular waves that result in better control over the timing of ovulation (Figure 2). Th is allows for more accurately timed breedings. At least two GnRH drugs are available, Cystorellin and Factrel. Both of these drugs contain 50 ug of GnRH/ml. The usually dosage is 100 ug/cow given by injection.

HCG is collected from the urine of pregnant women. Its action is on the mature follicle which has developed on the ovary. It will cause the mature follicle to rupture as in ovulation. HCG is often used to treat cystic ovaries. Common HCG drugs are HCG, Chorulon and Follutein. They come in a 10 ml vial that contains 10,000 units of HCG. The intramuscular dose (IM) for a cow is 10,000 units or the entire contents of the vial. These drugs can also be given intravenously (IV) at a reduced dose of 2,500 to 5,000 units/cow.

PFG is secreted by the uterus and regulates the lifespan of the corpus luteum (CL) (Figure 3). It moves from the uterus directly to the ovaries without circulating in the venous blood through the heart and back out to the ovaries through the ar terial blood. As PFG causes the regression of the CL, it also causes a decrease in the progesterone levels as progesterone is secreted by the active CL. PFG is used in the treatment of uterine infections, to cause abortions up to 100 days after breeding, expulsion of mummified fetus and for timing of breeding. Two PFG products, Lutaluze and Estrumate, are available. Keep in mind that there must be a CL present on one of the ovaries in order for PFG to work (Figure 4). For instance, when a CL is present at the time PFG is given, the cow will usually come into heat within 2-5 days. If the PFG is given early in the estrous cycle before a CL is formed and functional, no induced heat will occur. There is a system known as Target Breeding in which PFG is use d to synchronize the breeding time. In this system, 25 mg of PFG is given three times at 14 day intervals and then the cow is bred in 72-80 hours after the last PFG injection (Figure 5).

Estrogens have effects on both the ovaries and the uterus. They can correct anestrus in the absence of a follicular cyst. They are also recommended for treatment of a persistent CL, to empty the infected uterus and for the expulsion of a retain ed placenta or mummified fetus. ECP is an estrogen composed of estradiol cypionate. The recommended dose for treating anestrus is 3-5 mg given IM. For treatment of pyometra, retained placenta or mummified fetus, the recommended dosage is 10 mg IM. The do sage for persistent CL is 4 mg IM. Estrogens have been known to cause cystic ovaries and can cause estrus to occur without ovulation.

Oxytocin, often used to cause letdown of milk, also has the uterus as a target reproductive organ. It will cause the smooth muscles in the walls of the uterus to contract thus assisting in the emptying the uterus when the cervix is open. Oxytoc in is much more effective when the uterus is under estrogen control. The dosage is 1 ml IV or somewhat more when given IM.

In some instances, reproductive hormones are given in combination. This is the case with the Ovsynch program (Figure 6). With this program, GnRH is used to synchronize the follicular waves and PFG is used to bring the cow into heat for breeding. The c urrently recommended treatment plan is to give 50-100 ug of GnRH followed in 7 days with 25 mg PFG. After 36-48 hours, another dose of 50-100 ug of GnRH is given followed in 16-20 hours by timed breeding. Some cows may come into standing estrus after the PFG injection, but before or at the time of the second GnRH injection. It is recommended to breed these cows on standing estrus. When using the 50 ug dose, caution should be used to insure that part of the dose is not lost in large syringes or needles o r when drawing up the dose into the syringe from the vial. If less than 50 ug is injected, the plan will probably not work successfully.

With any reproductive synchronization program, it is well to remember that the conception rate will never be any greater than the conception rate following good heat detection. When synchronizing a group of cows, there must be a plan for breeding many cows within a short period of time. No plan will work with cows in poor body conditions or in non-cycling cows. Care should be taken to avoid major management changes such as mixing groups, virus vaccination or long transportations, as they will decreas e the effectiveness of the breeding plan. As always, good written records are needed to allow for an evaluation of the program.

Wise, prudent use of hormones can greatly enhance a dairy reproductive program. Prompt treatment of ovarian and uterine conditions can reduce the days open for their herd. Timed insemination programs will assure that all cows have at least one breedin g at a time determined by the dairymen, i.e. 75 days after calving. Hormones are costly so become familiar with the hormones being used on your dairy. When in doubt about the use of particular hormone consult your herd veterinarian.

Figure 1. Follicle on a bovine ovary. Top - Follicle on intact ovary. Middle - Ultrasound view of same ovary. Bottom - Cross-section of ovary cutting through the follicle.

Figure 2. Illustration of the three follicular waves over the course of a single estrous cycle in the cow. In each wave, a dominate follicle appears and then undergoes regression or atresia. In the final wave, the dominate follicle ruptures in ovulati on.

Figure 3. Ovary with corpus luteum or CL. Top - intact ovary with CL. Middle - ultrasound image of ovary with CL. Bottom - ovary cut through the CL.

Figure 4. Estrous cycle showing when PFG will regress the CL and bring a cow into heat.

Figure 5. Illustration of "Target Breeding" using a series of PFG injections.

Figure 6. Illustration of the "Ovsynch" system of time breeding using a combination of GnRH and PFG.