The pursuit of diversity in our pets diet may be doing more harm than good!
I decided to write about this topic of diverse (or varied) diets for reptiles – primarily snakes – because of the increasing number of posts I was reading from keepers concerned that their herp pets were not getting a sufficiently diverse diet. Many were trying to diversify their pet’s diet by adding things like chicken hearts and necks, tilapia or salmon fillets, whole (eviscerated) fish, frog legs and more. Some were actually collecting road kill!
I suspected, and then confirmed, that the impetus for this new trend came from some popular care sheet sights, and popular Facebook groups that are known to promote the highest possible care for our reptile and amphibian pets. They have a deserved reputation for good advice, so they deserve the respect they get. The problems come from well intentioned keepers who misinterpret the advice, or dont have the experience to keep it in perspective.
These newbies often adopt an almost religious zeal for their new faith in proper animal care. They can become quite fanatical about it! Before long the sound advice offered by the more experienced practitioners is warped into Holy Commandments that separate the devout from the heretics. And thats not helpful.
First, let me emphasize that there is nothing wrong with feeding a variety of prey items that reflect the species natural diet. In fact, this is the ideal. Unfortunately its also nearly impossible. Unless we feed wild prey collected from the same range and habitat that the species evolved in, we are not duplicating the nutrient mix it has evolved to utilize. Feeding frozen frog meat raised in crowded tanks and fed an artificial diet half a world away to a snake that would normally be feeding on whole, live leopard frogs in a US swamp with its belly full of June bugs is not the same thing. Yes they are both frogs, no the nutrition they offer is not even similar.
So the problem isnt that we want to feed a diverse diet to our animals. The problem is that trying to do so we can mess up in a way that is harmful to our animals. And importantly – it is often simply not necessary to pursue this goal of dietary diversity – at least not for most species, most of the time. Providing whole prey that is our domestic corollary to the animals natural wild prey, providing supplemental nutrients were necessary (dusting crickets, for example) is what our goal should be. Not diversity for diversities sake.
We human beings are frequently advised to eat a varied diet. We are told to eat a variety of grains and vegetables every day, etc. And I think we sort of internalize that advice and then extrapolate it to our animals. This is probably part of the motivation for the boom in diverse dog and cat foods. These too promised better nutrition and higher care but many turned out to be harmful, and the “grain-free” craze even led to a number of dogs’ deaths.
So what is important is that we not let the “idea” of feeding a diverse diet get in the way of understanding and providing good nutrition. And this is exactly whats happening. In pursuit of diversity some of us are providing lower quality diets that may not meet our animal’s nutritional needs, or may be exposing them to unnecessary risks.
I’ll try to explain with some examples. If you are raising a young garter snake on a diet of chopped worms and pink mice it is getting a “complete” and balanced diet. But lets say in the pursuit of a more varied diet you start offering bits of tilapia or salmon. Of course the garter (or hognose, or king snake, etc) may well eat the salmon, since all these species are eager feeders. But what you have done is replaced a nutritionally balanced meal with a nutritional deficient meal. You have increased variety but decreased nutrition.
This wont be a big deal if it happens a couple times per month. But feeding fish fillets is also easier, cheaper and less messy than feeding chopped worms and thawed pinks. And so it can easily become more than once a month. It can become the norm. And consider that the vast majority of wild garter snakes, let alone hog nose snakes, king snakes and rat snakes, will never eat a fish, why are we feeding fish to our captive snakes? Because it provides diversity?
The addition of these artificial food items also introduce risk. Almost all are treated with preservatives including carbon monoxide (illegal in most countries other than the US), and many are brined in salt water. Chickens are vaccinated and medicated. Why introduce those potential risks to our pets?
This is an important point: We know that well raised domestic mice *provide all the nutrition a snake needs to be perfectly healthy*. We know that from research that has examined the nutritional profile of domestic mice, and we know that because we have a few million captive snakes that have been raised on a diet of domestic mice and that displayed no disorders or diseases attributable to their diet. Note that the nutritional completeness depends on what the animal is fed. (1) So always source your herps’ food from the highest quality producers, not your neighbor kid feeding his mice collection cat or dog food.
“Although whole prey, including their organs, should be a *complete nutrient sufficient feed*, it is advised to add a small amount of a balanced vitamin and mineral supplement, especially when the birds are under stress.” (1) (More about supplements below)
“Mice and rats raised in captivity are usually considered to be a good quality food source. .. Feeding reptiles young lean mice that have been fed a high-quality, plant-based rodent chow provides a healthier diet…multivitamin and mineral supplementation for rodent feeders is usually not considered necessary, because properly fed rodents represent a complete diet (entire rodent ingested). In fact, one study showed no significant difference in size, weight, or bone density in two groups of hatchling corn snakes fed supplemented and nonsupplemented mice (Backner B, personal communication, 1991). “
Mader’s REPTILE AND AMPHIBIAN Medicine and Surgery P 174
Another quick example. People will often offer their snakes fish in various forms – again something the snakes would not be eating in nature. For no nutritional reason, they will, for example, feed their indigo snake trout from the fresh fish market, or feed their garter snake frozen silversides. In the interest of a diverse diet of course. These un-natural prey items cause gastro-intestinal problems that result in smelly, watery feces that we often hear keepers complain about. Why are we doing that? Well if you ask keepers, they will often tell you its because variety in the snakes diet is “important”. But variety, for it’s own sake, is not important and may in fact be harmful.
I want to touch on another issue that often comes up around this topic. And that is the claim that mice are “fatty” and therefore cause obesity in snakes. There are two important points to understand about this concern. The first is that adult mice are not significantly different than other often fed prey. Adult mice are 23% fat content, adult rats are 32% fat and adult quail are 32%. Day old chicks are 22% fat but add fat quickly and reach 38% by adulthood. Any animal that feeds on whole prey is going to be adapted to a high fat diet, so the fat content of these prey items should not be a problem for rodent eating snakes. For others, like garter snakes or water snakes, the rodents offered should be part of a diet that includes those species natural prey: whole fish, whole frogs and for garter snakes, worms. If you are feeding pieces of fish or frog legs simply because the whole animals are not available, then the keeper should carefully consider the addition of supplements.
No snakes should be allowed to become fat in our care. Fat snakes are overfed snakes. The easiest way to correct the problem is simply to reduce the amount of food that is fed. Some species are very enthusiastic feeders and will always seem to be hungry. That doesnt mean we need to feed it.
It is instructive to take a quick look at the natural diets of snakes. Reptiles and amphibians in general, and snakes in particular have a relatively limited range of foods they consume in nature. Even generalist species that may at times take a wider variety of prey tend to derive the majority of their nutrition from a relatively small number of prey species. Gopher snakes may eat almost exclusively small mammals for example. Hognose snakes may eat frogs and toads and small mammals. Garter snakes in the east of the US will live out their lives eating mostly frogs, toads and worms. This is of course a fraction of the number of species that a mammalian omnivore would consume. So our understanding of what diverse means should be relative to the animals natural diet, and not the diet of a mammalian omnivore.
Some species of snake have extremely restricted diets. How do snail eating snakes survive on just snails? Or even more remarkable, egg-eating snakes on just eggs? These snake species are able to derive sufficient nutrition to meet all their own physiological needs and produce young, yet consume only a single type of food their entire lives. Of course this isnt evidence for limiting our pet’s diet. Different species have the ability to extract different nutrients from their food. But this ability is something that has evolved over time and depends on the animal’s natural prey. (3) It is important to keep this in mind when we hear claims that a diverse diet is so important to our snakes!
Supplements are a consideration too. Its possible to do damage with supplements. Some natural prey has very high concentrations of vitamins – adult mice may have over 500,000 IU/kg of vitamin A, for example. And there is an upper safe limit to the amount of vitamin A we should be offering our animals. Not to mention that many of us are guilty of not being all that careful when using supplements. I know many of us couldn’t say how much we are adding or even why. We assume – wrongly – that the supplements are safe and effective regardless of dosage.
That said, the diets we feed our animals certainly are not what they have evolved to consume. The stomach contents of wild animals provide nutrients in quantities our captive prey items won’t – some more, some less. And of course in some cases – like to balance the unbalanced nutrients in crickets – we need supplements to just make sure the diet sufficient for normal bodily functions. So while its true that our animals generally dont need supplements, its also true that there may be benefits in some cases. The careful use of calcium, vitamin D, other vitamins and minerals from a high quality source is not something I would argue against.
The subject of diet in relation to enrichment has come up a few times. My initial reaction was that it was not a serious consideration. But I realized that that may be true more for snakes than for other herp species. Some lizard and tortoise species may be more stimulated by different foods than most snakes are, for example. So Ive decided to leave this area to the reader to experiment with and work out for themselves with their own animals. Keeping in mind of course the one big caveat I hope to communicate here: Nutritional needs should drive our animal’s diet, not the pursuit of some fictional good called diversity.
1. https://www.merckvetmanual.com/management-and-nutrition/nutrition-exotic-and-zoo-animals/nutrition-in-raptors#:~:text=Commonly%20fed%20items%20include%20mice,bred%20prey%20should%20be%20fed.
2. http://www.nal.usda.gov/awic/zoo/WholePreyFinal02May29.pdf
3. https://sora.unm.edu/sites/default/files/journals/jrr/v031n03/p00267-p00272.pdf
Spilotes pullatus Tiger Rat Snakes 