Retained Eggs - Dystocia
Dystocia is a relatively common malady in reptiles, occurring in lizards, snakes and chelonians.. There are many different causes, and in most cases, the cause goes undetected. DeNardo (1995) states that in his experience, dystocia occurs most often in first-time breeding females, females who have previously retained eggs, and female bearing infertile clutches. Dystocia can occur in live-bearing and ovoviviparous species; these are less common perhaps only because at this time there are fewer such species being bred in comparison with oviparous (egg-laying) species.
One general cause of dystocia may be due to the inability of the eggs to pass through the oviduct and cloaca. There may be an obstruction, the eggs may be too large or mal-positioned, the pelvis may be misshapen, or there may be obstructive masses such as abscesses or cystic calculi. Two or more eggs may be bound together, or a single egg may be exceptionally large or misshapen.
Dystocias can occur in the absence of obstructions or malformations. It is theorized that such retentions may be the result of one or more factors including poor husbandry, improper nesting site, improper temperatures, poor or inadequate diet (malnutrition), dehydration, and poor physical condition of the female. This latter is easily caused in, and remedied, in captivity.
Captive reptiles lead a very sedentary lifestyle compared to their wild counterparts, thus lack the muscle strength or tone to get all the eggs into position for laying and expelling them in a timely matter (from first egg to last). It is not uncommon, for example, for the last egg or two to be retained despite the successful and apparent ease with which the rest of the clutch was expelled by oviparous snakes.
In smaller snakes, recent oviposition (the repositioning of the eggs prior to laying) and the visible appearance of the swelling caused by the mass of eggs is a clue to the presence of eggs. In larger species such as pythons, eggs, especially retained eggs, are more difficult to see. It is more difficult to determine the retention of foetuses especially since entire clutches may be retained rather than just a few. Prolonged laying or birthing efforts and cloacal or oviductal prolapse (eversion of cloacal or oviductal tissue through the vent) are other signs of dystocia. Recently, improved ultrasonography techniques have been successfully used to determine the viability of foetuses in viviparous snakes, enabling the veterinarian to take the steps necessary to alleviate the situation by removing the nonviable tissue.
One common way to induce laying is to gently but firmly massaging the eggs out, one by one, by running the finger down the abdomen. This method is risky, however, in that it may rupture or cause a prolapse in the oviduct, could rupture the egg, and thus possibly cause death. If the egg can actually be seen at the vent extreme care may be taken to try to remove the egg, but such attempts may result in a broken egg with disastrous results for the female.
Posterior pituitary hormones have been used to start oviductal contractions. It is not effective, and may be dangerous, in females who are suffering from malformation of the pelvis or oviduct or who are carrying malformed, misshapen, enlarged eggs or foetus or who are suffering from an obstruction of the oviduct. Use of oxytocin (or the new experimental arginine vasotocin or aminosuberic arginine vasotocin) in such cases may cause egg or oviductal rupture or haemorrhage--and death. The overall efficacy of oxytocin, the most commonly administered hormone, varies between species, and can be hampered the longer the retention; it is most effective when administered within the first 48 hours. Oxytocin is administered by intramuscular or intracoelomic injection (5-30 IU/kg, but reports of efficacy in doses as low as 1 IU/kg have been reported in turtles). A second dose is often given 20-60 minutes after the first injection. Oxytocin's effectiveness is increased by the provision of the proper temperatures, so the female should be kept at the preferred body temperature for the species. Oxytocin is most effective in chelonians, less effective in lizards, and not as effective in snakes, with DeNardo attaining less than 50% success rate in snakes, more than 90% in chelonians.
Arginine vasotocin, and aminosuberic arginine vasotocin, a less effective but more stable form of arginine vasotocin, is the natural reptilian oxytocin. It is thus more effective than oxytocin, but arginine vasotocin is available only as a research drug and is quite expensive than oxytocin.
Other hormone treatments have been tried to increase the efficacy of oxytocin including the administration of progesterone and estrogen; there have been no studies to verify their usefulness. One recent study did show that pre-treatment with proprandol may increase the efficacy of labour-inducing drugs.
A common treatment for dystocia involves inserting a needle into the egg and aspirating the contents. The result is a far smaller egg which may be more easily passed through the oviduct and cloaca; oxytocin may be used to start contractions if they do not start on their own within a few hours or even a couple of days. Caution must be taken to not allow any of the egg contents to escape into the coelomic cavity. Aspiration must be done within the 48 hour period after cessation of natural laying attempts. After than short time, the contents of the eggs themselves begin to harden, making aspiration impossible. If the eggs are not expelled within 48 hours of aspiration, they must be surgically remove
If other attempts at inducing laying have failed, the reptile must be anaesthetized for surgical removal. Before cutting, a final attempt at manually manipulating the eggs may be tried owning to the reduced risk to the female due to the relaxation of the oviductal sphincter from the anaesthesia. As before, care must be taken to not push hard enough to cause a prolapse or rupture.
Depending upon what is found when the vet goes inside, the eggs only may be removed, or some or all the reproductive tissues may be removed. If there is no intention of breeding the female, the owner may wish to have an ovariosalingectomy done at the same time to prevent future incidents of binding.
Viability of Removed Eggs/Foetuses
Fertile eggs removed with oxytocin from non-dystocic females have been successfully incubated; eggs from females suffering from dystocia have generally not been successful. Foetuses removed through salpingotomy have also been successful.
Down the line...
The biggest factors determining female post-retention survival is her overall physical state. Most are severely weakened as the result of the dystocia. Those who started out healthy, in good nutritional, hydration and physical states are more likely to recover. Reptiles who have had only one of their reproductive tracts removed may often successfully reproduce in the future.
Personally speaking, if you are concerned about dystocia, if you are not sure if your female is gravid or not, if you are not sure if she is in distress or not, don't guess and try to wait it out: get her to a reptile vet and find out exactly (or as much as possible!) what you are dealing with.
DeNardo, D. (1995) Dystocias.
In Mader, D. (Ed.), Reptile Medicine and Surgery (pp. 370-374). Philadelphia, PA: W.B. Saunders Company.