Birds are oviparous, meaning they lay and incubate eggs. Chicks may be precocial (hatched with downy feathers and able to eat on their own soon after hatching) or altricial (featherless and completely dependent on being fed by parent birds until weaned). Passerine and psittacine birds are altricial. Sexual maturity occurs from 6 mo of age in smaller birds to 3–5 yr in larger parrots. Most hens have only a left ovary and oviduct and are heterogametic (the female determines the sex of the chick). The male has two testes located internally cranial to the cranial pole of the kidney.
Most wild birds have a specific breeding season. Captive and pet birds breed at any time based on environment (photoperiod), nutritional status, and absence or presence of a mate (bird) or perceived mate (human) and/or nest box. Females store calcium in their bones (hyperostosis), which is later used in egg shell production. Ovulation occurs in response to increasing levels of estrogen and luteinizing hormone. The oviduct is composed of four segments: the infundibulum, where fertilization occurs; the magnum, where albumen is deposited; the isthmus, where the inner and outer shell membrane is added; and the uterus (shell gland), where calcification of the shell occurs. The entire period of egg formation takes ~24 hr. Most pet birds lay 2 to 4 eggs in a clutch, although indeterminate layers such as cockatiels and budgerigars can produce much larger clutches.
Most pet birds are not sexually dimorphic, so determining the sex requires endoscopic examination or DNA sexing. Common reproductive problems in pet birds include behavioral issues, failure to reproduce, excessive egg production, dystocia (egg binding), impacted oviduct, egg yolk peritonitis, cloacal prolapse, and neoplasia.
Behavioral problems that can be related to reproductive issues include feather picking, mutilation, and excessive screaming. These behaviors can also occur for other reasons, so a full evaluation must be done to determine the cause. Behavioral problems are most common in hand-raised parrots overly bonded to their owners. Psittacines are intelligent, social animals. In the wild, most live in flocks, have a set breeding season (based on temperature, photoperiod, humidity), and raise chicks with their mate. In captivity, most pet birds are kept all year at stable temperatures and are provided adequate food, which is often high in fat. This can promote breeding behavior year round.
Many hand-raised parrots are overly bonded to their owner at sexual maturity, resulting in sexual frustration that may lead to over-grooming behaviors and excessive contact calls (screaming) when the owner leaves the room or house. Some of these over-stimulated (excessively handled and petted) birds begin laying eggs or masturbating early, leading to egg binding or cloacal prolapse (see below) along with feather destructive behavior or screaming.
Significant behavior modifications may need to be implemented (see Feather Destructive Behavior) along with conversion to a pelleted diet. In some cases, a GnRH agonist may be necessary to decrease production of reproductive hormones. This should ideally only be done along with implementing necessary behavioral modifications.
Excessive egg laying is when a bird has repeat clutches, lays more eggs than normal, or produces more eggs than is normal. It is common in small birds, eg, budgerigars, lovebirds, and especially cockatiels. Affected birds typically are on a high-fat and high-calorie diet. Other birds typically are housed either in the same cage or close by, or birds are overly bonded to the owner. They often have an extended photoperiod (>12 hr). In some color mutations, there may be a genetic predisposition.
Clinical signs may not be evident, with only a history of excessive egg laying, or the bird may present nonperching, weak, depressed, and tail bobbing (indicating dyspnea), with decreased defecation or voluminous droppings. Birds often have a wide-based stance, are broody, and may have pathologic fractures from hypocalcemia. Excessive egg laying, if untreated, often leads to more serious reproductive issues such as dystocia, impacted oviduct, egg-yolk peritonitis, or cloacal prolapse.
Diagnosis is based on the history, physical examination findings, high plasma calcium levels, and radiographic findings of hyperostosis and/or evidence of an egg. Reproductively active birds often have high cholesterol, triglyceride, and total protein concentrations.
Treatment involves decreasing day length to 8 hr of daylight, conversion to a pelleted diet, removal of nest boxes and any toys the bird may be overly bonded to, removal of any mate, and discussion with the owner of appropriate handling of their bird. Calcium supplementation and a GnRH agonist may be needed to reduce the production of reproductive hormones. Usually, leuprolide acetate (800 mcg/kg, IM, every 3 wk for three injections, then prn) is administered. If the above changes and medications are unsuccessful, then a salpingohysterectomy may be necessary. This will prevent egg laying but not always ovulation, because it is impossible in birds to remove all ovarian tissue. Prognosis is good with early cases that respond to management, dietary changes, and GnRH agonists.
Dystocia (egg binding) is a common occurrence in captive hens, most notably in cockatiels, budgerigars, and lovebirds. Usually, these birds are chronic egg layers, and calcium deficiency (resulting in misshapen or soft-shelled eggs) is a factor. Other causes include vitamin A deficiency, oviductal disease or neoplasia, abdominal wall herniation, being a first-time layer, and genetic factors. An inappropriate environment and lack of a nest box can be contributing factors for some birds. Egg binding may also be seen in large psittacines, although excessive egg laying is not as commonly associated with the condition in these birds. Obesity, general nutritional inadequacy, behavioral factors, and husbandry conditions may be involved. Egg-bound birds often present as emergencies. These birds should receive supportive care (ie, rehydration, parenteral calcium, increased humidity, and warmth) before attempting extraction of the egg.
Clinical signs include a bird on the bottom of the cage, depression, closed eyes, bobbing tail, and dyspnea. The abdomen may be distended. An egg is not always palpable. Diagnostic tests may need to wait until the bird is stable; they include a CBC, plasma biochemical profile (including ionized and total calcium), and radiographs. These tests may need to be done stepwise in a critical patient.
Medical treatment includes fluid therapy, parenteral calcium supplementation, analgesics, and/or NSAIDs, and continued maintenance in a warm humid incubator. Oxytocin and the avian equivalent arginine vasotocin both cause uterine contractions and induce oviposition, as can prostaglandins F or E. If the egg is adherent to the uterine wall or unable to be passed (often due to swelling, adhesions, or collection of feces and urates), administration of these drugs could theoretically lead to uterine rupture, but this has rarely been reported.
If medical management fails, then sedation, inhalant anesthesia, and manual extraction may be required. With the bird under anesthesia, the cloaca is lubricated with sterile jelly. Barring adherence of the egg to the uterus, steady digital pressure applied between the end of the sternum and the egg will cause the slow descent of the egg. At this point, the uterus will often evert and reveal the white pinhole where the uterine opening is located. This opening will gradually dilate. Very seldom will any additional pressure or manipulation be required. After the egg is delivered, the uterus typically will normally involute. If oviposition does not occur with digital pressure or because of a soft-shelled egg, ovocentesis is indicated. After aspiration, firmer shells are collapsed and carefully removed or allowed to pass. Postoperative care includes antibiotics, NSAIDs, and a GnRH agonist to reduce further egg laying. After egg extraction, the hen may continue to be depressed, with labored breathing, and often will not appear clinically normal for up to 24 hr. A second egg may be produced by the following day, so repeated palpation is indicated.
Surgical intervention (salpingohysterectomy) is warranted if the egg is severely adhered to the oviduct, multiple eggs are present, or the egg is ectopic. Prognosis for egg binding is fair to good if medical treatment or manual extraction of the egg is effective. Husbandry, nutritional, and behavioral issues as discussed under excessive egg laying (see above) need to be addressed.
An impacted oviduct is often a sequela of dystocia or salpingitis. The oviduct becomes impacted with excess mucin, albumen, and soft-shelled or malformed eggs. These materials often become adhered to the oviduct wall and become inspissated. Clinical signs are depression, anorexia, distended abdomen, and possibly dyspnea.
Diagnosis is based on a history of chronic egg laying or dystocia. Imaging (radiographs, CT scan, or ultrasound) may reveal an enlarged oviduct. Hyperostosis may be present. The bird may have a leukocytosis and high total protein, cholesterol, and triglyceride concentrations. Treatment is supportive (fluids, analgesics, NSAIDs, and antibiotics). Surgery is recommended but is high risk.
Birds with cystic ovarian disease often present with a history of previous egg production, but egg laying may not have occurred for several years. Cystic ovarian disease is most commonly seen in budgerigars and canaries.
Clinical signs may include depression, inactivity, abdominal distention, ascites, and often dyspnea. Abdominal palpation often reveals distention with ascitic fluid.
Diagnosis is similar to other reproductive diseases. The fluid is usually a transudate, although it should be examined for evidence of secondary infection or egg-yolk peritonitis. Careful aspiration of fluid from the ventral midline may relieve respiratory distress. Imaging (radiographs or ultrasound) when the bird is stable will often demonstrate hyperostosis of the femurs and other long bones. On the lateral view, the ventriculus will be displaced cranially, and a space-occupying mass will be noted in the renal and gonadal area. Ultrasonography can often detect cystic follicles, in addition to normal follicular development.
Treatment is supportive care, abdominocentesis if ascites is present, antibiotics, and GnRH agonists to reduce reproductive hormone production, stimulate atresia of the follicles, and decrease cyst size and production. Surgery may not be needed if there is no concurrent infection or neoplasia.
Egg yolk coelomitis is another common sequela of chronic reproductive disease. It can occur after salpingohysterectomy because of the inability to completely remove the ovary and the potential for ovulation to occur into the coelomic cavity. Other causes are ectopic ovulation, salpingitis, neoplasia, cystic hyperplasia, or ruptured oviduct. Egg yolk, along with bacteria (eg, Escherichia coli, Staphylococcus) in the coelomic cavity results in infection. Egg yolk coelomitis causes a severe inflammatory reaction and can lead to an egg-related pancreatitis or a yolk emboli (which can resemble a stroke). This occurs most commonly in cockatiels.
Clinical signs are similar to other reproductive disorders, but typically abdominal distention and ascites are present. Birds often present severely compromised and require supportive care before diagnostic testing. A leukocytosis and monocytosis may be present. Imaging (radiographs or ultrasound) may reveal an enlarged oviduct or a fluid-filled abdomen. Endoscopic examination may be diagnostic but should be done only by an experienced clinician in a bird with ascites. Abdominocentesis may need to be performed to relieve dyspnea. Other treatments include fluids, antibiotics, analgesics, anti-inflammatories, a warm incubator, and oxygen as needed. Many birds will improve with supportive care and antibiotics, but some may require salpingohysterectomy. Prognosis is fair with medical management and becomes guarded to grave with surgical intervention.
Cloacal prolapse can occur in any bird that strains frequently. It is seen in egg-bound hens and in adult cockatoos, typically males. The exact cause is not known, but the following characteristics have been associated with most cases: 1) hand-raised birds, 2) delayed weaning or continued begging for food, 3) close attachment to at least one person, 4) signs of either a child/parent or a mate/mate relationship with the owner, who may not be aware of these signs, and 5) a tendency to hold the feces in the vent for prolonged periods (eg, overnight), rather than defecating in the cage or when the bird has been taught to defecate on command. Cockatoos independent of people do not have this medical problem.
If detected and treated early, surgery combined with behavioral modification may correct the problem and prevent secondary infections and other complications. Treatment includes cleaning exposed tissue, carefully debriding any necrotic or infected tissue, using hyperosmotic fluids to reduce swelling, and gently replacing the tissue. Stay or transcutaneous sutures may be required for several days and are more effective if combined with GnRH agonists and changes in management (eg, reduced handling of pet cockatoos by owners). Owners may be unwilling to alter their behavior, because often their attraction to the bird is because the bird is willing to allow stroking and cuddling. If the bird still perceives its owner as either a parent or mate, it will continue to strain and the problem will likely recur. Behaviors that should be avoided include stroking the bird, especially on the back (ie, petting); feeding the bird warm foods or food by hand or mouth; and cuddling the bird close to the body. If an owner is serious about trying to change their bird’s behavioral patterns, consultation with a board-certified veterinary behaviorist who is experienced with psittacines is advisable.
In severe cases, where the vent is flaccid, vent reduction and/or cloacopexy may need to be performed but should only be done with behavior modification. Females may require salpingohysterectomy, because the vent reduction and cloacopexy may not allow passage of an egg.
Most owners do not breed their pet birds, but reproductive failure is an issue for aviculturists who do. When evaluating a pair of birds for reproductive failure, a complete history is important. Is this a bonded pair (do they sit close to each other and allopreen, etc)? How long have they been together? Have they had a successful clutch in the past? What is their diet? Are the cage size, nest box, and perches appropriate for the species of bird? Most pet birds prefer an enclosed nest box and a stable perch for breeding. Is the owner certain of the sex? One of the most common reasons birds do not reproduce is same-sex pairs. Confirming the sex by DNA testing or endoscopic examination (to evaluate health and status of reproductive organs) is important. Common findings during endoscopy include same-sex pairings, immature birds, and reproductive disease. Physical examination, hematologic testing, and biochemical profiles are recommended to determine overall health. Treatment will depend on the examination and diagnostic findings and may include alterations in the environment or medical therapy if indicated.
In many cases of reproductive disease, birds with moderate to severe disease require intensive nursing and supportive care. Often, physical examination and diagnostic tests must be postponed until the bird is stabilized in a warm (85°–90°F) oxygen incubator with supportive care. Procedures may need to be done in a stepwise fashion over time to minimize stress. Treatments may include warm parenteral fluid therapy, nutritional support, analgesics, anti-inflammatories, and antimicrobials (based on results of a Gram stain or culture and sensitivity testing). Some birds may require surgery. Reproductive surgery in birds is complicated by the difficulty in removing the ovary. Because of the position of the ovary cranial to the kidney, near the left adrenal gland and major vasculature, removing the entire ovary is not possible. The standard approach to the avian reproductive tract is a left coeliotomy. Endoscopic orchidectomy and salpingohysterectomy have been described but require specialized training.