Ovarian cysts reduce reproductive efficiency on almost every dairy farm in the United States. It has been estimated that the incidence of ovarian cysts ranges from 5 to 20 percent in most herds. A recent Wisconsin field study of dairy herds reported that the incidence of ovarian cysts ranged from a low of 16.2 to a high of 47.4 percent. Mature cows have a higher incidence (39 percent) of ovarian cysts than do first-calf heifers (11 percent). Breeding age heifers have a lower incidence of ovarian cysts (3-6 percent). It is interesting to note that beef cows have a relatively low incidence of cystic ovarian disease. Because ovarian cysts reduce reproductive efficiency, they are a source of severe economic loss in most dairy herds.
Ovarian cysts (Figure 1) are follicular structures having a diameter of at least 2.5 centimeters (about 1 inch) that are present for 10 or more days on the ovaries in the absence of a functional corpus luteum (CL). The only practical method to detect cystic ovarian disease is by rectal palpation of the cow's reproductive tract. This fact emphasizes the importance of regularly scheduled herd health examinations of postpartum cows by a veterinarian skilled in rectal palpation. Ovarian cysts can be classified as either follicular cysts or luteinized follicular cysts. Table 1 lists the characteristics of follicular and luteinized follicular cysts. Cystic corpora lutea (CL with a fluid filled cavity) should not be confused with ovarian cysts because the former are not pathological and function normally both during the estrous cycle and pregnancy.
Cows with ovarian cysts have an abnormal pattern of estrous behavior (see Table 1), and, in many cases, the absence of estrus (anestrus) is a common symptom of a cow with cystic ovarian disease. The physical appearance of cows with ovarian cysts is usually not different from that of other cows. However, the following are general symptoms that cows with ovarian cysts may have: 1) thick, cresty neck, 2) little or no muscle tone in the vulva, vagina and uterus, 3) relaxation of the sacroiliac and sacrosciatic ligaments, resulting in the appearance of an elevated tailhead and 4) abrupt changes in milk production. It should be noted that these general symptoms are useful only in a preliminary diagnosis of cystic ovarian disease and that rectal palpation is required for a definitive diagnosis.
Parameter Follicular Cysts Luteinized Follicular Cysts ---------------------------------------------------------------------- Structure thin-walled, with thick-walled, with luteal thickened theca layer tissue lining inside of and variable amount follicle of granulosa cells Number of cysts and single or multiple on usually single on one ovary distribution on ovaries one or both ovaries Occurrence of cyst approximately 70% of approximately 30% of the type cases cases Serum and milk pro - usually low usually high gesterone concentra- tions Behavior of cows anestrus (majority) or usually anestrus erratic estrus or nym- phomania Chance of recovery 30-70 % if occurrence same without treatment is before first post- partum ovulation 20-30 % if occurrence same is after first post- partum ovulation Recommended treat- 100 ug GnRH (may same ment be followed 9 days later by one dose of a prostaglandin [PG] product) Days to estrus after 21 days without PG same treatment (range 9-30 days) approximately 12 same days with a PG product Response to treat - 60-70% 70-80% ment Conception rate at 45-60% same first estrus after treat - ment -----------------------------------------------------------------------
The exact factors that are responsible for cyst formation are unknown. However, most researchers believe that a malfunction in the preovulatory release of luteinizing hormone (LH) is responsible. When cysts develop, follicles enlarge to an abnormal size instead of ovulating and releasing an egg (Figure 2). The presence of cysts prevents the cow from having normal 21 day estrous cycles. Therefore, the cow cannot be bred, and pregnancy will be delayed until the cyst(s) regresses spontaneously or responds to treatment.
In a Swedish study, Al sires were culled if their daughters had ovarian cysts. Over a 20-year period (1954-1974) the national incidence of cysts in Sweden declined from 10 to 3 percent. This decline in the incidence of ovarian cysts implicates genetics as having a major role in the transmission of cystic ovarian disease from one generation to the next. Therefore, culling cows and heifers with ovarian cysts would appear to be one method of permanently decreasing the occurrence of ovarian cysts in dairy herds. Unfortunately, many cystic cows are also the high producers, making effective culling difficult to implement in many cases.
To date, comprehensive studies have not demonstrated a link between nutrition and ovarian cysts in dairy cattle when experiments were conducted with properly balanced rations. In other words, if the ration meets all of the nutrient requirements of the cow, additional amounts of selected nutrients (i.e., Beta-carotene and selenium) will not revent ovarian cysts. However, it is of utmost importance that rations be properly balanced and provided in adequate amounts to meet the requirements of milking cows.
Although it is a common belief that high producers may be more prone to develop ovarian cysts, no experimental data supports this contention. Increased milk production may be a result of the altered hormone environment that occurs with ovarian cysts rather than a cause of ovarian cysts.
In the early part of this century, manual rupture (via rectal palpation) was used as a treatment for ovarian cysts. Recovery rates were approximately 45 percent. However, because of possible hemorrhaging, formation of adhesions around the ovary and the advent of hormonal treatments, manual rupture is used less frequently than in the past. More recently, hormones having high LH - like activity have been successfully used as a treatment for ovarian cysts. Initially, pregnant mare's serum gonadotropin (PMSG) and human chronic gonadotropin (hCG) were utilized, but, due to their large molecular weight, some cows developed antibodies against these products and retreatments were not always successful. However, hCG is still a commonly used treatment for ovarian cysts.
Currently, gonadotropin releasing hormone (GnRH) is the most frequently recommended treatment for cows with ovarian cysts because it causes the pituitary to release LH and does not result in antibody formation. Table 1 lists the treatments for follicular and luteinized follicular cysts and describes the expected outcome after treatment. Because a high proportion of cysts spontaneously regress during the early postpar tum period, treatments are usually not administered until after 30 days postpartum. The GnRH treatment causes luteinization of the cyst, and the subsequent prostaglandin treatment of the luteinized cyst causes regression of that structure.
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