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Endocrine Abnormalities


Endocrine Abnormalities

Cross section of a beef heifer's udder.

Cystic Ovaries

Cystic ovaries are found in cattle and other species whereby ovarian follicles develop but do not ovulate at the correct time. Ovarian follicular cysts, also called cystic ovarian degeneration, are of particular concern in the dairy cattle industry because it is considered one of the most important causes for reproductive failure. There are several relationships between lactation and cystic ovaries. Obviously, if an animal fails to ovulate, then it cannot become pregnant, therefore limiting the opportunity to initiate a new lactation cycle. In contrast, dairy cows with the cystic ovary condition often appear to produce more milk in the current lactation, than those that do not have the condition.  

Incidence of cystic ovaries in dairy cattle is about 12% (citations in the literature range from 3 to nearly 30%). This compares to about 6% for dystocia (difficulties in calving), over 3% for twinning, 4% for stillbirths, over 9% for retained placenta, 5.5% for anovulation (delayed interval to first postpartum ovulation is longer than 4 weeks), over 17% for reproductive tract infections, 21% for metritis (inflammation of the uterus), and 37% for cows that have one or more of the above disorders combined with metabolic diseases (milk fever, ketosis, displaced abomasums, etc).

An anovulatory follicle may persist, or undergo luteinization. In the former case, the cows with cystic follicles may exhibit clinical signs of nymphomania, resulting from the persistently elevated secretion of estrogen. In the case of luteal cysts, the cysts secrete excess progesterone and the cows tend to be anestus. The mechanisms by which ovarian cysts may occur all point to some abnormality of the hypothalamic-hypophyseal-ovarian axis (pituitary-hypothalamus-ovarian axis). This may occur in response to exogenous factors that change the normal endocrine interrelationships or endogenous factors. Treatment of ovarian cysts in cattle usually employs administration of some hormone preparation that intervenes in the disrupted endogenous feedback mechanisms and jump-starts the normal system. The hypophyseal releasing hormone, GnRH, is often used to elicit a surge in luteinizing hormone (LH) to force ovulation of the follicular cysts. Alternatively, human chroionic gonadotropin (hCG), which has LH-like activity, can cause ovulation of the cystic follicles. For luteal cysts, a luteolytic agent such as prostaglandin F2alpha may be used to lyse the luteal cyst.

Typically, follicular cysts maintain elevated estrogen concentrations in the blood. Estradiol concentrations are usually sustained in the range of 4 to 10 picogram/milliliter for an extended period. This compares with about 10 to 50 pg/ml estradiol for the few days prior to ovulation and 1 to 5 pg/ml during the luteal phase of the cycle. Estradiol concentrations in blood of pregnant cows can increase up to 450 pg/ml. However, other estrogens also are secreted by the placenta and can increase the effective estrogen concentration substantially during pregnancy. Luteal cysts secrete progesterone, but only slightly elevate blood progesterone concentrations, averaging less than 1 ng/ml. Normal progesterone concentrations in the cycling cow range from as low as about 0.1 nanogram/ml during the proestrus and estrus phases of the cycle to 8 to 10 ng/ml during the luteal phase.

Ovarian tumors and tumors that result in elevated estrogen

Ovarian tumors are not common in cattle. When ovarian tumors are identified in cattle the most common type is the granulose cell tumor, however, a variety of other tumor types also have been identified in bovine ovaries. Some ovarian tumors can secrete excessive amounts of estrogen, while others may secrete more progesterone. Blood concentrations of hundreds of pg/ml to over 1 ng/ml of estrogen have been noted in heifers with ovarian tumors. Chronic nymphomania, mammary development, and relaxation of pelvic ligaments such as seen near calving (raising of the tailhead) are some of the symptoms of ovarian tumors in cattle. The contralateral ovary often is nonfunctional and atrophied. Removal of the ovary containing the tumor is a potential solution, although it seems that sometimes the other ovary is sufficiently compromised by the condition that it does not then become functionally active.


Pituitary tumors and galactorrhea

The literature on pituitary tumors and the mammary gland mostly come from he human health arena. Prolactinomas are the most frequent pituitary tumor. They are observed mostly in females between 20 and 50 years of age and are even less common in children and adolescents. Elevated blood prolactin concentrations in patients with prolactinomas are a primary indicator of the condition and can range form less than 100 micrograms/ml to 3500 µg/ml. Normal concentrations of prolactin in

Treatment of prolactinomas typically includes some type of dopamine agonist, such as bomocriptine (a synthetic ergot alkaloid) or quinagolide (a nonergot dopamine agonist). These reduce serum prolactin concentrations in about 90% of the cases and shrink about 60% of the tumors. Cabergoline (a synthetic ergoline) has also been used successfully on those tumors resistant to the other dopamine agonists.

Hyperprolacinemia also has been reported associated with treatment of protease inhibitors as part of antiviral therapy in relation to treatment for HIV-1 infection. Those patients with hyperprolacinemia also reported galactorrhea (inappropriate lactation). However, some of these patients also were taking other drugs associated with galactorrhea (fluoxetine or metoclopramide), so it is difficult to determine the role of the protease inhibitors in the induction of lactation.

 
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