Egg binding is a common and potentially life-threatening condition in laying hens that occurs when an egg fails to pass through the oviduct at a normal rate.
Egg binding often develops secondary to conditions that cause chronic or excessive straining. It can progress to dystocia, which is a mechanical obstruction during egg laying. A retained egg can place significant pressure on structures within the pelvic canal, potentially obstructing the passage of feces and urates. This may lead to ileus, renal dysfunction, and pressure-induced necrosis of the oviduct wall.
A variety of underlying causes and contributing factors may lead to egg binding, including:
- Hypocalcemia: Inadequate calcium levels can result in thin-shelled or shell-less eggs, which are more difficult to pass. The oviductal muscles may conform to the egg rather than effectively expelling it, increasing the risk of retention. Causes of hypocalcemia include poor or imbalanced nutrition, insufficient dietary calcium, lead toxicity, or diets high in oxalates or phytates.
- Excessive egg production
- Onset of lay: Hens that have just begun laying are at increased risk.
- Oviductal infections: Conditions such as salpingitis can cause inflammation and dysfunction of the oviduct.
- Vitamin E and selenium deficiencies
- Pullets that start laying prematurely
- Environmental stressors:Heat stress, overcrowding, bullying, overmating can all contribute.
- Trauma: Injury to the oviduct or vent.
- Obesity: Excess fat in the abdominal or vent region can reduce oviduct elasticity.
- Malformed or oversized eggs: These can overstretch and weaken uterine muscles.
- Ovarian tumors: Masses may narrow the oviduct and physically obstruct egg passage.
If left untreated, the condition can lead to complications such as chronic egg retention, granuloma formation, uterine impaction, ectopic eggs, egg yolk peritonitis, and death.
Signs and Symptoms of Egg Binding in Chickens
Clinical signs vary depending on severity, the size of the hen, and the presence of complications. Smaller hens are often more severely affected and may be at higher risk of sudden death. Signs typically worsen the longer the egg is retained.
Common clinical signs include:
- Frequent nestbox sitting (note: this can resemble broodiness).
- Changes in roosting behavior, such as sleeping in the nest box or on the ground.
- Abdominal straining without producing an egg.
- Cloacal prolapse
- Depression: The hen may isolate herself from the other birds, act less engaged and social, close their eyes frequently like their resting, and/or eat less or nothing at all.
- Abdominal distension
- Abnormal posture, including a wide stance or upright “penguin-like” position
- Increased respiratory effort (due to pressure on air sacs).
- Cyanosis, with the comb darkening to a deep red, purple, or blue.
- Tail wagging
- Decreased or absent feces and urates
- Lameness progressing to paresis
If the egg is lodged within the pelvic canal, it may compress nearby blood vessels, kidneys, and the sciatic nerve.
Diagnosis
Diagnosis is based on history, clinical signs and physical exam. Radiographs and/or ultrasound can help provide confirmation of the presence and location of the egg, in addition to the size.
- History: Absence of egg and previous egg quality issues such as soft-shelled, thin-shelled, odd-shaped and/or lash eggs.
- Physical examination: Coelomic palpation reveals the presence of a firm egg-like mass. This method will only identify shelled eggs located in the caudal oviduct. Soft-shelled eggs or eggs that are cranial positioned can be missed.
- Radiography: Useful for confirming the presence of shelled eggs and egg sizes.
- Ultrasonography: Is necessary for detecting soft-shelled or shell-less eggs not visible on radiographs.
- Bloodwork: A CBC and chemistry panel may help identify hypocalcemia or underlying disease
Treatment for Egg Binding
Treatment depends on the timeline, cause, severity of signs, and physical state of the hen. In mild, early-stage cases, hens may pass the egg with at-home supportive care, such as placement in a warm, quiet, stress-free environment and calcium supplementation. If the egg is not passed within 24 hours, or if clinical signs worsen, immediate veterinary care is essential.
Medical support typically consists of calcium supplementation, fluid therapy, vent lubrication, pain management, and oxygen therapy if in respiratory distress.
Inducing oviposition through the use of pharmacologic agents is an option but carry risk. These agents include:
- Prostaglandin E2 (PGE2) gel: Helps relax the uterovaginal sphincter and stimulates oviductal contractions. There is a risk of uterine rupture, particularly if the egg is large.
- Prostaglandin F2 alpha (dinoprost): Stimulates smooth muscle contraction in the oviduct and/or expel soft-shelled eggs. It doesn't relax the uterovaginal sphincter like PGE2.
- Oxytocin: Stimulates smooth muscle contraction in the oviduct but has no effect on relaxing the uterovaginal sphincter. It carries the highest risk of uterine rupture and sudden death. Its use in birds is controversial as it is not an avian hormone.
Note: None of the above agents should be used in cases of ectopic eggs, mechanical obstruction of the egg, involvement of large eggs, or oviductal damage (constriction, torsion, or rupture).
If the hen is unable to pass the egg on her own within 24-48 hours, is excessively straining or distressed, more invasive methods for egg removal are necessary and include manual egg manipulation, ovocentesis, and surgery.
Ovocentesis involves aspirating the egg contents to collapse it, facilitating its passage or minimizing adverse effects if it cannot be expelled.
Surgery may be required if medical management fails, in cases of ectopic eggs, cloacal and/or oviductal prolapse, torsion or necrosis, or if the egg is preventing the passage of waste through the vent.
Gonadotropin-releasing hormone (GnRH) agonists such as leuprolide acetate and/or deslorelin (Suprelorin F) are an option to help prevent the hen from continuing to lay eggs. Note that Suprelorin F is only approved for treating adrenal disease in ferrets in the United States. They are used off label with discretion.
