Chapter 173 Avian Reproductive Tract Disorders
Avian reproductive disorders are a result of complex combinations of hormonal, physiologic, and behavioral actions reacting to photoperiods, food availability, and availability of nest sites. Environmental influences unique to captivity may induce reproductive and hormonal activity in several ways. For instance, artificial lighting may interfere with the normal photoperiod and annual light cycles, resulting in inappropriate cycling. Food is typically available ad libitum in captivity, and it often is high-fat, calorically dense seed or foods high in simple carbohydrates, such as corn and fruit. These foods may actually stimulate reproduction. A lack of an appropriate mate may also cause reproductive problems. Most pet birds are not intended for breeding and do not have mates. As a result, some of these birds select an abnormal mate such as their human cohabitants or cage furniture. Along with all of these common environmental influences, there may be genetic factors that contribute to a lack of normal reproductive hormonal balance.
FEMALE REPRODUCTIVE DISORDERS
See Figure 173-1 for reproductive anatomy of the female bird.
Chronic or Excessive Egg Laying
Etiology
• Chronic egg laying in pet birds occurs when a hen lays repeated clutches or a larger-than-normal number of eggs per clutch without regard to the presence of a mate or accurate breeding season. This process often physically exhausts the reproductive tract and is a serious metabolic drain, particularly on calcium stores. These factors may predispose the hen to egg binding, yolk peritonitis, and osteoporosis.
Diagnosis
Diagnosis of chronic egg laying is based on history and physical examination.
Physical Examination
• Palpate the abdomen. An egg is sometimes palpable in the coelom. The abdomen often has a doughy consistency due to uterine distension.
Treatment
Medical therapy for chronic egg laying focuses on stopping egg production while removing predisposing stimuli and correcting any secondary diseases that may be present. Pharmacologic, behavioral, nutritional, environmental, and surgical options are used alone or in combination, depending on the needs of the individual patient. Pharmacologic options have included medroxyprogesterone acetate, levonorgestrel, human chorionic gonadotropin, testosterone, and leuprolide acetate.
Pharmacologic Therapy (Table 173-1)
Leuprolide Acetate
• Leuprolide acetate (Lupron Depot, TAP Pharmaceuticals) is a long-acting gonadotropin-releasing hormone (GnRH) analogue. Principles for use of Lupron have been extrapolated from use in humans and other species and are often effective in controlling ovulation in birds.
• Administer 150 to 800 μg/kg IM every 14 days. Three doses are usually sufficient to inhibit further egg laying. Repeat treatment may be needed if signs return.
Table 173-1 MEDICAL THERAPY FOR REPRODUCTIVE DISORDERS
| Drug | Dosage | Comments |
|---|---|---|
| Leuprolide acetate | 150–800 mg/kg IM | Administered every 14 days; three doses are usually adequate |
| Human chorionic gonadotropin | 250–500 IU/kg IM on days 1, 3, and 7 | Stable in refrigerator 60 days |
| 500–1000 IU/kg IM | If a second egg is laid, repeat dose on day 3; if a third egg is laid, repeat dose on day 7 | |
| Levonorgestrel | Not recommended | |
| Medroxyprogesterone | Not recommended | |
| Arginine vasotocin | 0.01–1.0 mg/kg IM | Stable in standard freezer |
| Prostaglandin E (Prepidil Gel) | 0.1 ml/100 g | May freeze into aliquots and thaw |
| 0.002–0.1 mg/kg | Applied topically prior to administration; relaxes uterovaginal sphincter while inducing uterine contractions | |
| Prostaglandin F-2-alpha (Lutalyse) | 0.02–0.1 mg/kg IM | May not relax uterovaginal sphincter when inducing uterine contractions |
| Topically applied to prolapsed uterine tissue to stop hemorrhage and shrink tissues |
Human Chorionic Gonadotropin
• Human chorionic gonadotropin (hCG) (Pregnyl, Organon) has been used successful to inhibit egg laying with few side effects; however, it has not been consistently effective and patients may become refractory to treatment.
• Reported dosage regimens vary. Administration of 250 to 500 IU/kg IM on days 1, 3, and 7 has been effective to prevent laying. Alternatively, administer 500 to 1000 IU/kg IM after the first egg is laid. If another egg is laid, repeat the injection on day 3; if a third egg is laid, repeat the injection on day 7.
Other Hormonal Treatments
• Medroxyprogesterone acetate, although often effective, may cause serious side effects such as polyuria and polydipsia, obesity, lethargy, hepatic lipidosis, diabetes mellitus, hepatic cirrhosis, and death. Therefore, it is not recommended.
• Testosterone therapy interrupts the ovulatory cycle, but it has inconsistent results and is contraindicated in patients with liver disease.
Environmental Modification
• Remove from the enclosure nest sites, toys, and other items toward which the bird has a sexual affinity. Prohibit access to the nesting environment or materials such as a box, other dark cavities, or shredded papers.
• If the bird is showing nesting behavior and laying eggs in a designated site, leave the eggs in the “nest” for the duration of the normal incubation period for each species. Removal of the eggs may stimulate the hen to lay more eggs to replace those removed.
• Remove any perceived or actual mate from the cage or room. In some species, such as the cockatiel, both visual and auditory separation from an actual or perceived mate may be necessary.
• A “one-person bird,” which has a single household person who exclusively or primarily handles and cares for it, should potentially be viewed as having a “mate relationship” with that person. This may serve as a trigger for reproductively driven behaviors. Advise this person to avoid stimulatory petting such as rubbing the pelvis, dorsum, and cloacal regions.
• Encourage interactive behaviors that simulate a “flock relationship,” such as the bird being handled by several people in the household.
• Periodically change or rotate the cage location and furniture (toys, perches, food dishes) to discourage territorial behavior and limit reproductive drive in response to a perceived “nest site.”
• Correct any nutritional problems to improve the hen’s overall dietary plane and reduce the severity of metabolic drain. Dietary alteration and reduction of caloric intake appears to anecdotally reduce or stop egg production. This nutritional effect often is achieved by converting the pet bird from a seed-based diet to a formulated one. The exact reason for this effect is unknown, but it is common practice in poultry to reduce feed intake to stop egg production and induce molting.
Polyostotic Hyperostosis
Etiology
• Physiologic osteomyelosclerosis is the deposition of calcium stores in medullary bone for future use in egg production.
• Polyostotic hyperostosis differs from physiologic osteomyelosclerosis in that this condition occurs in non-laying hens and cocks as a result of pathologic conditions.
• The pathogenesis of polyostotic hyperostosis still is unclear. Many affected birds exhibit concurrent reproductive-associated activity or may suffer from reproductive-associated disease conditions.
Diagnosis
• History and physical exam may reveal lethargy, depression, reduced appetite, and reproductively driven behaviors.
• Serum chemistries typically demonstrate hypercalcemia. The bird may be normocalcemic or hypocalcemic if on a calcium-deficient diet.
Egg Binding and Dystocia
Definition
• Egg binding is defined as the failure of an egg to pass through the oviduct within a normal period of time.
• Most companion birds lay eggs at intervals of greater than 24 hours, and individuals may vary further.
• This variability may make it difficult to determine if there is a problem in the early stages of this disease.
• The most common anatomic areas for this obstruction to occur are the distal uterus, vagina, and vaginal-cloacal junction. See Figure 173-2 for other anatomic landmarks associated with egg binding.
Etiology
• Causes of egg binding may include chronic egg laying, oviductal muscle dysfunction secondary to excessive egg laying, disorders of calcium metabolism, vitamin E and selenium deficiencies, malnutrition, obesity, inadequate exercise and muscle strength, malformed eggs, mechanical tears or damage to the oviduct, oviductal infections, systemic disease, genetic predisposition, and environmental stressors.
• Dystocia also may result when a developing egg in the distal oviduct obstructs the cloaca or causes oviductal tissue to prolapse.
Clinical Signs
• Cockatiels, canaries, and finches are most commonly affected and usually present with more severe clinical signs, possibly due to their small size.
• Clinical signs associated with egg binding and dystocia vary according to severity, size of the bird affected, and degree of secondary complications.
• Common signs include acute depression, abdominal straining, persistent tail wagging, a wide stance, pelvic limb paresis or paralysis, failure to perch, abdominal distension, urine or urate retention, dyspnea, and sudden death.
Diagnosis
Physical Examination
• Palpate the abdomen for the presence of an egg. Palpable eggs may be located within the oviduct or ectopically within the coelom. A combination of abdominal palpation, cloacal examination, radiographs, coelomic ultrasound, laparoscopy, and/or laparotomy may be required to determine the egg’s position.
Diagnostic Imaging
• Obtain abdominal radiographs. Shelled eggs are visible radiographically. Eggs are typically located in the distal oviduct, in the region of the uterus.
• Osteomyelosclerosis of the femurs, tibiotarsi, radii, ulnas, and/or spine may be visible. A soft tissue density suggestive of an enlarged ovary in the region of the ovary may be noted, supportive of a reproductively active hen.
• Coelomic ultrasound often will reveal an egg and may identify soft-shelled or non-shelled egg(s) that may not have been identifiable on radiographs. Again, there may be several eggs visible within the coelom. Follicles may be visible on the ovary, indicating the potential for further ovulation and egg formation.
Laboratory Evaluation
• A hematologic analysis and serum chemistries are useful to identify any predisposing and secondary diseases.
• A complete blood count may reveal a leukocytosis with a relative heterophilia if there is a concurrent inflammatory or infectious process.
• Serum chemistries may demonstrate elevated aminotransferase and creatinine phosphokinase due to skeletal muscle enzyme leakage from tissue damage or as a result of reduced food consumption and a hypermetabolic state.
Treatment
Therapy varies with history, severity of clinical signs, and diagnostic test results.
Supportive Care
• Provide supportive care, including a warm and humid environment, parenteral calcium, fluid therapy, and nutritional support.
• Administer broad-spectrum antibiotics if an infectious etiology is suspected or if the integrity of the oviduct may be compromised.
• Administer analgesics if the patient appears to be in pain or if clinical knowledge of the patient’s condition suggests that pain may be a part of the pathologic state.
Pharmacologic Therapy (See Table 173-1)
• Prostaglandin and hormonal therapy may be used to induce oviductal contractions. This may result in expulsion of the egg if the contractility of the oviduct is sufficient to expel the egg, the uterus is intact, the egg is within the oviduct, and there is no obstruction such as a neoplastic mass, granuloma, or egg adhered to the oviduct.
• Prostaglandin and hormonal therapy requires exogenous calcium to be effective. Because many of these patients are severely hypocalcemic due to either malnutrition or chronic egg laying, supplemental calcium may be required prior to administration of these medications.
Prostaglandin E-2
• Apply prostaglandin E-2 (PGE2) (dinoprostone) gel (Prepidil Gel, Upjohn) topically, per cloaca, to the uterovaginal sphincter, at a dose of 0.1 ml per 100-g bird.
• PGE2 causes relaxation of the uterovaginal sphincter while inducing oviductal contractions. These contractions usually expel the egg within 15 minutes.
• After the egg is expelled, flush the cloaca with warm water or saline to remove remaining gel, prevent further discomfort from continued uterine contractions, and minimize systemic side effects.
Prostaglandin F-2-alpha and Other Hormonal Therapy
• Administration of prostaglandin F-2-alpha (PGF2a), oxytocin, or arginine vasotocin (AVT) will also cause powerful uterine contractions.
• These treatments are administered parenterally, rather than topically, and are more likely to cause systemic side effects such as hypertension, bronchoconstriction, and general smooth-muscle stimulation.
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