Breeding Iguanas



There are an estimated 7.3 million reptile-owning households in the United States. Compare this, if you will, with the 50 to 55 million households with dogs and cats as pets. It is clear that reptiles are fast becoming a favorite among pet owners. Of interest, and it is of no surprise, that the green iguana (Iguana iguana) is currently one of the most popular reptile pets.

 As with other pets, iguana owners will inevitably want to breed their charges. The problem is, iguanas can be difficult to breed in captivity. Even some zoos, with their highly skilled herpetologists, have a hard time getting these animals to consistently reproduce in captivity. If they do breed, and the eggs are fertile, oviposition (egg laying) and incubation represent yet another obstacle. Many iguanas sold through pet stores advertised as "captive born" are the progeny of gravid females that were caught in the wild, then allowed to oviposit in captivity.


Photo by Cary Bass/Wikimedia

A reddish green iguana.


Why is this a problem for the novice iguana owner? Just as in chickens, female iguanas will still reproductively cycle and ovulate, even without the presence of a male. In chickens, we want them to ovulate because that is what produces the eggs we eat. However, in captive pet iguanas, unless we are trying to breed them, we really don't want them to ovulate.

Ovulation with the subsequent egg laying is often fraught with medical problems. Reproduction in the iguana is complicated, involving the interplay between temperature, light cycles, humidity, season, availability of adequate nesting sites and more. Although iguanas are often sold as a "beginner pet," they are not. Of particular interest at the moment is the subject of whether it is necessary to spay pet iguanas. That is, should we surgically alter these animals like we do dogs and cats in order to prevent them from breeding?

With the increasing popularity of iguanas being kept as pets, there is more demand on the veterinary community to offer the best medical care. In dogs and cats, it is recommended to have them neutered prior to their reaching puberty. Neutering refers to either castrating the male of the species (removing the testicles) or performing a spay in the female (called an ovariohysterectomy, which is the removal of the ovaries and uterus). Note: Iguanas do not have a uterus, rather, they have a shell gland that serves a similar purpose. Either of these procedures renders the pet infertile and incapable of reproduction. In mammals, after successful completion of either of these surgeries, the pet is often more "mellow" compared to intact conspecifics.

There are several other motivating factors that play a significant role in the decision of whether or not to sterilize dogs and cats. Of particular medical significance, it is well known that spaying the female dog prior to her first heat will eliminate the possibility of mammary (breast) cancer. This is quite serious, as mammary cancer is a common disease in the older female dog, and can potentially kill the pet if not caught and treated in time. This, of course, has not been a problem in iguanas.

Of additional importance, in dogs and cats, neutering prevents unwanted pregnancies, thereby cutting down on the overpopulation problems currently plaguing the country. Millions of dogs and cats are killed each year at pounds and shelters because there are simply too many animals and not enough homes. Granted, we do not have the same problems with feral iguanas running rampant through our streets, eating out of trash cans in the alley, begging at the back doors of dimly lit restaurants and being slaughtered on the nation's streets and freeways by automobiles. In fact, with reptiles, doesn't it seem that we usually encourage captive-breeding of the animals to cut down on the importation and exportation of wild-caught animals and decrease the numbers of sick and stressed lizards?

The problem here is one of health care and home management of this wild pet (yes, iguanas are wild animals; they are not domesticated like dogs and cats, and, at best, can only be called "tame"). There is still relatively little that we know about these creatures in the wild, and until we can fully understand their needs and requirements in the great outdoors, it will be impossible to match these demands in captivity.

 The Green Iguana Reproductive Cycle

Adult female iguanas will usually cycle once per year. There are some reports of iguanas ovipositing in both late fall and early spring. Whether that represents two distinct seasons or just a late laying (fall) is a matter of debate. Herpetological veterinarians in northern latitudes state that reproduction occurs in the spring, coincident with warmer days and longer day lengths.

 Pre-Ovulatory Conditions

Female iguanas in good health will experience one of two potential outcomes as a result of having developed follicles (developing eggs). If the female is in good body flesh or good body condition, her ovaries may develop, produce follicles, then resorb them if the conditions are not right for laying, with no further or lingering problems. The cycle will repeat again the following breeding season.
 
In the wild, females display elaborate nesting behavior. They lay their eggs in the sandy soil of riverbanks. If an appropriate beach area is not available, they have been seen swimming miles upstream or downstream to find such a place. If space is at a premium, female iguanas have been seen sharing beach space and even nesting space with other females.

In captivity, these animals may begin to display nest-searching and nest-building behavior. Pet iguanas have been known to dig up planters in the house in an attempt to build a nest. If an appropriate place is not available, some females are capable of resorbing their ova and recycling for the following laying season.

 The problem is that a female will normally become anorectic, or lose her appetite, for about four weeks prior to egg laying. The developing eggs take up so much space within their coelomic cavity, they act like a space occupying mass, and there is no room left for stomach contents. In a healthy animal, this is not a problem, because they can easily go four weeks without a meal. The problem arises in females that have been kept under marginal or poor nutrition, because they do not have the body reserves to last for four weeks of nest finding and digging.

 These animals will often collapse. It is not uncommon, as well, for these animals to show signs of hypocalcemic tetany, as their body tries to maintain the eggs at the expense of their calcium homeostasis. This occurs when a female iguana utilizes all of her body's calcium reserves to form the necessary shells around the developing eggs. In those animals that have no or low calcium reserves, tetany results. The muscles will twitch and tremor, taking on a convulsion-like appearance when the animal is excited or stressed.

Calcium is an extremely critical mineral. We hear about calcium and phosphorus all the time when discussing reptile diets. Calcium is responsible for bone growth and strength, nerve conduction, muscle contraction, blood clotting and more. If the body has a need for more calcium, as in the case of a female producing eggs, it will draw extra calcium from its own bones, the major storage site for calcium. When the storage levels get down about 40 percent of normal, problems start to develop. In adult animals, you see signs of tetany or generalized tremors. These can be quite subtle or, if the animal is stressed, quite dramatic.

Evolution selected those animals that will spare no expense to reproduce. In ecological terms, it is better for one animal to die if its death can ensure continuation of the species (the production of a clutch of eggs). These cases of hypocalcemic tetany are an emergency. They must be medically managed, stabilized and then, if the owners are willing, taken to surgery to have the source of the problem, the reproductive tract, removed.

Post-Ovulatory Conditions

In the second scenario with the healthy female iguana, the ova will eventually ovulate and be transported to the shell gland where they undergo calcification. (Note: Iguana eggs do not harden like a bird's egg; they have a leathery texture.) Once all of this occurs, again, assuming that the female is in appropriate calcium homeostasis, she will ultimately oviposit, or lay her eggs, if the housing in correct (proper nesting sites available).

As mentioned, calcium is extremely important in maintaining normal physiology. This includes the muscle contraction needed for egg laying. Some females that have ample calcium stores to produce the shelled eggs may run out of the necessary mineral when it comes time to start contraction of their shell glands, a necessary step in egg laying.

These iguanas may also experience hypocalcemic tetany. However, these patients are not as critical as those in the pre-ovulatory tetany. They still must be managed medically, but once stabilized it may be possible to induce oviposition and avoid the need for surgery.

The key is to warm the animal to near the middle to high end of its preferred optimum body temperature, which for green iguanas is in the mid-90s. Once at the core temperature, the patient starts on oral or injectable calcium supplements, depending on the severity of the condition. Once stabilized, which may take a few hours to a few days, the animal can be induced to lay, assuming all other medical factors are in check or, if not, taken to surgery for removal of the eggs.

Determining Pre- Versus Post-Ovulatory Conditions

 The most important factor to determine when deciding to manage the iguana medically or surgically is whether it has a pre-ovulatory or post-ovulatory condition.
 
In pre-ovulatory egg retention, the animal develops mature follicles, but due to some physiological intervention, there is follicular stasis prior to actual ovulation. The ova remain on the ovaries and do not resorb. If left in that condition, the follicular membranes will coalesce, forming one large mass of friable yolk. These will readily rupture (which can happen with rough handling), causing severe inflammation of the coelomic cavity, and death of the patient if not treated immediately and aggressively.

In post-ovulatory egg-retention, the ova have actually ovulated and then been picked up by the shell glands. They may or may not acquire a shell at this time, but for whatever reason, oviposition, or egg laying, does not occur.

It is essential that these two conditions be differentiated, because pre-ovulatory egg retention is not responsive to medical therapy. All of the injectable calcium and egg-laying hormones in the world are not going to help the patient. In fact, administering oxytocin, a hormone used to induce egg laying, may possibly do harm from the straining that the drug induces.

You can't always differentiate between the two different conditions. It is sometimes possible to distinguish between pre- and post-ovulatory egg retention by taking an X-ray. The only way you can tell for certain is if you see actual shell membranes around the eggs. If you do not see membranes, it may still be a post-ovulatory condition, it is just in the stage prior to the deposition of the shell. Oxytocin should never be tried unless the individual shell membranes are visible on an X-ray.

Initial Examination of the Patient

 From my perspective, I would have to say that the majority of iguana owners have no idea that their pet is gravid (pregnant). The majority of cases that I see go like this:
 
Mr. John Doe brings in his pet iguana because it's not eating. It may be bloated, it may have difficulty walking, and it may be twitching. Mr. Doe does not even know the sex of his pet (good thing he named it Iggy). Most of the time, I can tell the sex just by looking at the animal from across the room. Mature male iguanas have a very typical appearance: broad heads; large, ornate opercular scales; extensive, fanlike gular flap; impressive dorsal spines; and often, especially in breeding season, brilliant colors.

Females, on the other hand, are usually more defined, having smaller, streamlined heads; small opercular scales, gular flaps and dorsal spines; and often, a pear-shaped abdomen. Gently turning the patient over and examining the femoral pores will usually be the definitive test. Mature males have larger, better-developed femoral pores, many times excreting a wax-like substance. Caution, however, as I have seen many males with fairly small pores, and more than an occasional female with very masculine-sized pores. It is best to take all the factors into consideration when assessing gender.

If you suspect that your pet may be gravid, have it examined by an experienced herpetoculturist or your favorite herp veterinarian. Just as in people, it is important to prepare for the event by ensuring proper nutrition (if your pet is still eating), housing, temperature, humidity and nesting material. Even in those animals that have stopped eating, I recommend balanced pre-natal vitamins, or at least a calcium supplement.

At the time an animal is brought to me for a "pregnancy" evaluation, the first thing I do is try to determine the stage of gestation. Actual gestation (the time it takes from the beginning of egg formation until egg laying) takes about eight weeks. For the first four weeks, the animal does not show many overt changes other than an initial increase in appetite and a slight weight gain. If in good condition, the gravid female will usually stop eating during the last four weeks of gestation. As mentioned, this is because the egg masses essentially fill the coelomic cavity, not leaving room for stomach filling.

Treatment

f the iguana is in a pre-ovulatory stage and is in good condition, I prefer to send her home with husbandry and nutrition instructions. I always send the gravid iguana home with a calcium supplement, specifically, Neocalglucon (calcium glubionate, Sandoz). The recommended dose is 1 cc/kg, orally, twice per day. This is a fruit-flavored liquid, and the patients generally take it voluntarily.

If the patient has stopped eating, I have the owners try to estimate how long this has been going on. Using that information, I can then calculate when the pregnancy will be in its eighth week (remember, four weeks of eating plus four weeks of noneating).

If the animal gets worse before the estimated eight weeks are up, or if it starts eating (a sign that the female has resorbed her ova), I have them come back in for a recheck at that time. If by the eight-week mark there is no change in appetite, and no eggs have been produced, I have them come back for either medical management (necessitates a repeat X-ray to determine if the eggs are now post-ovulatory) or surgery.

If at the eight-week recheck the animal is still pre-ovulatory, or as sometimes is the case, it cannot be determined, I recommend that the owners start to think about having the pet spayed. If the animal is doing well and the owner wants to continue with supportive care, I review with them the importance of proper husbandry, and again send them home with instructions to watch for signs of impending oviposition or signs of trouble.

If at the time of the eight-week recheck the eggs are now post-ovulatory, or if the patient is doing poorly (lethargic, weight loss, tremors), I recommend hospitalization and attempting to induce oviposition with calcium and oxytocin. I will typically set a limit of 24 hours. If I can't induce the iguana to lay its eggs within the first 24 hours of hospitalization I recommend taking the patient to surgery.

A cesarean section (C-section) is a medical process where the surgeon removes the babies (or eggs) but leaves the reproductive tract intact. In a spay procedure, the surgeon removes the entire reproductive tract. When performed properly, a C-section leaves the animal reproductively intact for future reproduction. A spay renders the animal incapable of breeding.

Since iguanas are not ecologically delicate animals, I recommend spaying them rather than trying to salvage their future reproductive potential. It has been my experience that most of the iguanas that have egg-related problems once will have them again.

During the actual surgery, I remove the entire reproductive tract. This includes both shell glands and both ovaries. After removing the organs, I suture the skin on the iguana's abdomen. Reptile skin heals differently than mammalian skin. Rather than suturing the skin cut end to cut end, reptile skin has to be apposed underside to underside. Although this looks strange at first, it offers the best healing potential. Once the sutures have been removed (they must be left in at least four weeks), the skin flattens out, looking like normal belly skin.

It is not uncommon for the post-operative iguana to undergo a shed shortly after the surgery. Remember that these animals have been under severe duress for several weeks, and many have not eaten for over a month. Suddenly, post surgery, they have energy and an appetite to match. Many patients will shed off their belly sutures before they ever get back for a recheck.

Summary

The important thing to remember is this: Not all gravid iguanas are egg-bound! It is a common misconception that all iguanas brought to veterinarians gravid are in life-threatening danger of being unable to pass eggs. All too frequently, I hear about iguanas that have been spayed because their owner was told that "it was egg-bound, and it would die unless it had surgery."

If you remember the normal stages of pregnancy, you will be better prepared to assess your pet's need for surgery. Some veterinarians are advocating spaying all iguanas. As previously mentioned, in mammals early spaying helps prevent many serious health problems such as mammary cancer and pyometra (uterine infections). Although the former is not a problem in iguanas, the shell glands are susceptible to disease. I don't think there is anything wrong with spaying young, healthy iguanas. It sure is a lot easier and safer than doing surgery later on an animal that is depressed, hypocalcemic and near death.

I have many clients who have very healthy pet iguanas that are many years old. Each year their iguanas lay infertile eggs as a matter of routine. The choice should be made on an individual basis. If cost is a factor, it is usually less expensive to have the procedure performed prior to maturity, and much less costly than waiting until the animal is ill, requiring oftentimes substantial additional supportive care.

The bottom line is this: It is important that iguana owners plan ahead. You can prevent most of the anticipated problems by providing proper housing and nutrition, and offering an appropriate nesting substrate during the breeding season.


References

Barten, S.L. 1996. "Lizards," from Reptile Medicine and Surgery. Mader, D.R. (ed), pp. 47-61. Saunders, Philadelphia, PA.

DeNardo, D. 1996. "Dystocias," from Reptile Medicine and Surgery. Mader, D.R. (ed), pp. 370-373. Saunders, Philadelphia, PA.

DeNardo, D. 1996. "Reproductive biology," from Reptile Medicine and Surgery. Mader, D.R. (ed), pp. 212-223. Saunders, Philadelphia, PA.

Dugan, B. 1982. "The mating behavior of the green iguana, Iguana iguana," from Iguanas of the World. Burghardt, G.M. and Rand, A.S. (eds), pp. 320-341. Noyes, Park Ridge, NJ.

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