Reference Library

"Going Cystic"
The Vet's Bag
By Stuart J. Burns, D.V.M.

It is obvious that the function of a brood cow is to produce calves, but sometimes we overlook the obvious for invalid reasons such as pedigree, show record, horn growth or color. The old time cattlemen probably had it right when they insisted that a cow bring a calf to the pen every year or she was off the ranch. Such rigid rules are sometimes difficult for the small breeder with few animals to follow, but history suggests that all of us should. The development of "cystic ovaries" is a condition that will illustrate this point rather well. Treatment is possible, reasonably effective, inexpensive, but is it in the best interest of the breed to treat it or remove the animal from the gene pool?

Cystic ovaries are most frequently detected in the higher producing cows i.e., those that tend to milk the most and produce the big high weaning weight calves. It is most common in mature cows, most commonly seen fairly soon after calving, and more common in fall and winter months. The exact cause of a cow "going cystic" remains unclear, but all the clinical evidence points to an inadequate release of luteinizing hormone (LH) from the pituitary gland located at the base of her brain. The function of LH is to cause a mature follicle to ovulate so the cow can become pregnant. A follicle is a fluid filled structure that contains an ovum (egg) and produces estrogen.

There are two types of "cysts" that can result from an inadequate LII surge, both producing similar clinical signs in the cow and both respond to the same treatment. A follicular cyst results when the cow formed a follicle but the LH surge was not great enough to cause ovulation. The follicle attempts to produce progesterone, but it does so only in small amounts. The second type of a cyst is a luteal cyst. A normal corpus luteum (a solid mass of tissue that replaces the follicle) is formed after ovulation and this is the source of progesterone that will maintain the pregnancy if one is present. Again, if the LII surge is insufficient, the cow may make it through ovulation but falter with a poor quality corpus luteum. The end result, for a simple way to think of it, is that the cow becomes stuck in "reproductive neutral" and cannot shift gears from one normal cycle to the next until she becomes pregnant. Treatment can be approached from several different directions, all being aimed at stimulating a normal progesterone response that hopefully will be followed by a normal cycle
and pregnancy.

The cow may do one of two things that will indicate a problem exists. She may simply not return to heat and otherwise be normal. The herdsman will assume she is pregnant and this cow will escape detection unless examined for pregnancy. This is one of many reasons that cows should be confirmed pregnant after 60 days or longer after the bulls are taken out. Cows found open and cystic that show no other signs except failure to return to estrus can then be treated or culled. The second behavior that some cows will display, and few herdsmen will overlook, is persistent nymphomania. This cow appears to be in heat all the time and may prove to be a disrupting influence in the herd. With either behavior, after a variable period of time, the affected cow may develop some changes in her body type that make her begin to appear masculine. Treatment, if elected, is most rewarding if initiated before these changes are observed.

The normal sequence of events leading to ovulation requires gonadotropin releasing hormone (GmRH) to be released from the brain which stimulates the pituitary gland to release LH. This hormone causes ovulation followed by progesterone secretion from the ovary. As previously identified, a "cystic" cow is probably the result of an inadequate LH surge with an end result of failure to ovulate followed by low progesterone production. The treatment can be approached from several points in this chain of events, all having the same goal of producing a normal corpus luteum to provide a normal progesterone level. We should be aware that 40 to 50 percent of affected cows will correct with no treatment.

The cow can be given progesterone for 14 to 21 days. Signs of nymphomania will cease in 36 to 72 hours after onset of treatment. This causes the cow's pituitary to store up LHI which is released when treatment stops. The resulting LII surge causes ovulation and normal fertile cycle. Attempt to breed the cow on this cycle.

A second means of treatment is to inject 10,000 u human chorionic gonadotropin (HCG), which provides a strong LH surge that hopefully will cause an ovulation followed by normal cycles.

A third, more recent approach uses an injection of 100 micrograms GnRH. This injection causes a pituitary release of LII of 2-4 hour duration which equals the normal event and usually causes an ovulation. These treatments all have the same goal and appear to be very similar in effectiveness. About 2/3 of treated cows will have a normal fertile estrus within 20-30 days of treatment and they should be bred on that estrus.

Texas Longhorns cows do not seem to become 'cystic" as frequently as some other breeds, but factual data is not available to support this clinical impression. The purebred breeder should give some thought to the merits of treating a "cystic" cow compared to culling her. There does appear to be a hereditary influence on the frequency of cystic ovaries. From breeds with greater numbers and more complete records than Texas Longhorns. it appears that 27% of daughters of affected cows will become 'cystic". while only 9% of daughters from normal cows will be so affected, a threefold difference. Further evidence of a genetic influence is supported by the observation that the incidence of ovarian cysts decrease from 10% to 3% when only bulls produced from "non-cystic families" of cows were used for breeding. This is a situation where a good argument for not treating the cow can be made, even though inexpensive and reasonably satisfactory treatment protocols are available.