Metabolic Bone Disease Prevention | Husbandry Errors

Authored by: Christina Miller CAHT/RVT, RLAT, BSc

Preventing Husbandry Errors

Diet

Determining what aspect of an affected pet’s husbandry went wrong may be painfully obvious to the knowledgeable herpetoculturist, or more subtle and requiring a trained eye. Recall that we need to consider aspects of our husbandry that involve nutrition and lighting. Dietary obtainment of calcium and phosphorus, and acquisition of vitamin D3 versus the animal producing its own D3 depends greatly on the animal’s habits. We will first take an approach based on dietary preferences to explore the common husbandry errors that lead to MBD.

1. 

   “Whitethroatedmonitor” by Calibas – Own work. Licensed under Public domain via Wikimedia Commons.

   Carnivores: This dietary category includes all predators whose diet is made up of other animals, such as mammals, birds, fish, invertebrates, or other reptiles and amphibians. Herps being fed whole vertebrate prey generally do not suffer from nutritional problems as long as the prey animals are healthy and suited to the predator (Stahl and Donoghue 2010).With regards to metabolic bone diseases, the most common problems occur when prey is sectioned into pieces. Muscle meat, for example, is very calcium-poor and phosphorus-rich, a simple but important dietary imbalance (Girling 2003, Stahl and Donoghue 2010), and an improper calcium-to-phosphorus ratio (Ca:P) alone may cause a metabolic bone disease (Frye 1984). Animals being fed ground meat, which is almost exclusively muscle meat in many cases, will suffer calcium deficiency without supplementation or a change to a more suitable diet (there are other vitamins and minerals that are gravely deficient in muscle meat). Feeding neonatal rodents (“pinky” mice and rats) has been linked to the development of calcium imbalances as their calcium content is poorer than older individuals (Douglas et al. 1994).It has been observed that carnivores absorb vitamin D3 that was formed and/or stored by their prey. Several carnivorous species (such as the Corn snake, Pantherophis guttatus (Acierno et al. 2008) have been demonstrated to produce their own vitamin D3 when exposed to UV-B lighting, even nocturnal species such as the Ball Python (Python regius) (Hedley and Eatwell 2013). While there are countless references stating that these whole-prey eating species (and many others) do not require exposure to ultraviolet light in captivity (as we assume that they are obtaining adequate amounts of vitamin D3 from their prey), it should be questioned whether provision of UV-B could be beneficial. More on this topic later.

2. Insectivores: Insectivores are a “subset” of carnivores that eat predominantly insects and perhaps other invertebrates. The term “invertivore” has been tossed about in herpetoculture to better describe animals that eat a range of invertebrates including earthworms, spiders which are arachnids, crustaceans like sow bugs, and other non-insect invertebrate species.Insectivores are mentioned here because their typical preys in captivity are normally calcium-poor. Many commercially-raised insects possess an inverted Ca:P (Allen and Oftedal 2003) as well as other deficiencies (Finke 2002) that must be corrected through appropriate gut-loading and supplementation (Finke 2003). Failure to appropriately gut-load and/or supplement, as well as improper feeding technique may result in MBD.
3. Herbivores: Completely herbivorous reptiles have what can be argued as the most complex nutritional needs of any captive herps. Most vegetables and fruits that are commonly found in grocery stores for human consumption are calcium-poor, phosphorus-rich, and/or contain calcium antinutrients (such as oxalates and phytates) in significant quantities. We can provide nutritionally-sound diets in captivity, but it takes a bit of work to get it right.Folivores, or foliage-eating animals, like the Green Iguana (Iguana iguana), do best on a diet that is composed mostly of calcium-rich, antinutrient-poor leafy greens, with other “compatible” vegetables and fruits added to round out the salad (Hatfield 1996, Kaplan 2002). Many commercially-available fruits and vegetables have an inverted Ca:P (Allen and Oftedal 2003), so supplementation with calcium is often necessary.Of great importance with Green Iguanas in particular is that oral vitamin D3 does not appear to be absorbed effectively, and UV-B light is required to prevent metabolic bone diseases (Allen and Oftedal 2003). It is unclear whether this idiosyncrasy is unique to Green Iguanas, or if it is a commonality in folivorous or perhaps all herbivorous reptiles.Graminivores, or grass-eating species, that hail from grasslands, savannah, and other similar habitats, graze almost exclusively on grasses and some other low-growing plants. Tortoises from these arid habitats such as the Horsfield or Russian Tortoise (Testudo horsfieldii), the Leopard Tortoise (Geochelone pardalis), African Spur-thighed or Sulcata Tortoise (Geochelone sulcata), and the Desert Tortoise (Gopherus agassizii) have similar dietary requirements with some species-specific needs. They thrive on calcium-rich, low-protein foliage and grasses. Hays and grasses as well as select grocery store greens should make up the bulk of these species’ diets (Highfield 2000, 2002). Generalizations should always be made with caution in the herp world: Always investigate species-specific husbandry information. Note that some species may be opportunistic omnivores in the wild, occasionally ingesting carrion or other animal matter. However, this is not necessary to maintain healthy captives and has a great potential to be harmful (McArthur and Barrows 2004).
4. 

   Bearded Dragon (Pogona vitticeps) enjoying a salad composed of calcium-rich leafy vegetables.

   Omnivores: A catch-all dietary classification of species that prey on more than one ecological trophic level (e.g. “plants and animals”) in varying proportions. For example, Chinese Water Dragons (Physignathus cocincinus) (Stahl and Donoghue 2010) and Veiled Chameleons (Chamaeleo calyptratus) (Gamble 2001) appear to be predominantly insectivorous or perhaps carnivorous, and ingest plant matter opportunistically which classifies them as omnivores. Other commonly kept pet species, the Inland Bearded Dragon (Pogona vitticeps) (Pianka and Vitt 2006) and Red-eared Slider (Trachemys scripta elegans) (Bouchard and Bjorndal 2006) start out life predominantly carnivorous with an ontogenetic shift to a predominantly herbivorous diet. Careful attention must be paid to the requirements of both dietary categories to ensure the provision of appropriate nutrition in captivity.

Supplements

While supplements are useful to help correct nutritional shortcomings in diet ingredients or available prey, they should not be relied on alone for provision of adequate nutrition. In herbivore salads, for example, it is impractical and probably near-impossible to accurately measure how much supplement is ingested (Allen and Oftedal 2003), due to varied adhesion to different salad components, selection of specific salad components, and loss to the environment. Similarly, with animal prey is it difficult to assess how much powdered supplement is sticking to invertebrate prey, and how much is lost to the environment.

Dusting insect prey with calcium powder helps to compensate for their poor Ca:P, ideally fed during the animal’s preferred activity period to avoid loss of powder to the environment.

Unsurprisingly, recommendations for supplementation vary greatly among veterinarians, herpetoculturists, and the makers of said supplements (Lennox 2002). There is no single perfect formula for supplementing any captive herp diet, and the need for supplementation will vary according to the ingredients or prey in the given diet. There is also little data available on the digestibility of many of these supplement mixes (which likely varies in different species), leaving the bioavailability of the provided nutrients in question.

Relying solely on vitamin D3 supplementation to make up for a nutritional deficiency is a potentially hazardous practice. When the body is producing its own D3 through interactions with UV-B light, there are molecular “failsafe” mechanisms in place that stop the body from producing an excess of this vitamin to prevent toxicity (Holick 2004). No such mechanism exists for dietary D3, and toxicities are common. There exists guidelines as to how much D3 can produce toxicities, for example, 4000 IU of D3 per kilogram of food can produce toxicity in some species (NRC 1987). Most commercially-available supplements unfortunately do not list their vitamin D3 content which makes for more supplementation guesswork. Nutrient toxicities, and not just vitamin D3, can occur with supplementation (Stahl and Donoghue 2010). Hypervitaminosis D from chronic over supplementation leads to soft tissue calcification (Donoghue 2006), which will eventually lead to the death of the animal due to complications (pseudogout, renal failure, etc.).

Lighting 

As discussed in Part I, broad spectrum lighting that includes ultraviolet B (UV-B) wavelengths is critical for the good health of many species. Natural sunlight includes UV-B wavelengths (range from 315-280 nm) which react with the animal’s skin to eventually synthesize the active form of vitamin D3 (see Part I for a review of this process) (Gehrmann 2006). There exist artificial light sources that emulate portions of the sun’s spectrum to provide the same health benefits.

This UVB radiometer is measuring local irradiance of UV-B wavelengths. On the left, a mercury vapour bulb that has been in use for about a year in a Green Iguana’s enclosure. On the right, natural sunlight on a slightly overcast day in temperate Nova Scotia, Canada.

Natural and unfiltered sunlight should ideally be provided to every captive herp, but this is unfeasible in many climates. When access to the sun is limited or impossible, ultraviolet-B lighting must be provided to any species where there is sufficient evidence that it is necessary for proper bone development and maintenance (Gehrmann 2006). We should be constantly reevaluating the value of broad spectrum lighting in species that traditionally have been maintained in captivity without it as there may be benefits to these animals. As indicated above, even species that are traditionally kept and bred rather successfully (Cornsnakes (Acierno et al. 2008) and Ball Pythons (Hedley and Eatwell 2013)) without UV-B lighting in captivity show a capacity to use UV-B lighting for vitamin D3 production. Further investigation is needed to determine if providing UV-B to these and other species offers tangible health benefits. In the meantime, it can be argued that it is beneficial to provide UV-B to any captive herp in some capacity. (Please note that lighting for captive herps is not as simple as UV-B or no UV-B. Ultraviolet A, the colour rendering index of a light source, as well as the photoperiod or number of daylight hours is also important. Lighting for herps is quite a complex topic!)

Providing UV-B lighting is not as simple as setting up a light and hoping for the best. These devices must be used appropriately, and the following guidelines are a good starting point:

1. Never allow a glass or plastic barrier to occlude your broad spectrum light. Most glass and plastic filter 99-100% of UV radiation, even if visible light may pass through. The exception is quartz glass (what UV-B producing bulbs are made of) and acrylic glass made without UV-blocking additives (Baines et al. 2009).
2. Ultraviolet irradiance decreases with distance from the source. Most bulbs are effective at a distance of less than 30 cm (12″) from the basking spot, but always read the manufacturer’s recommendations for the product you are using. However, because bulbs may also produce small amounts of harmful UV-C radiation near the bulb’s surface, a minimum distance of 10 cm (4″) has been suggested (Baines et al. 2009).
3. Screen or mesh enclosures or lids will physically block some UV from reaching the animal (Baines et al. 2009). If you have mesh or screen between your broad spectrum bulb and the animal, ensure that the herp can get relatively close to the bulb, or add a reflector to increase local UV irradiance at the basking spot.
4. Herps are never in direct sunlight for the entire day. Always ensure that the herp can choose a location as a refuge from UV light exposure (Gehrmann 2006). While UV-B is essential for good health, excessive exposure absolutely has risks such as tissue damage to the skin and eyes (Gardiner et al. 2009, Remenyek et al. 1999, Tang et al. 1994, Webb et al. 1989, Zuclich 1989). This may be most relevant in amphibians, whose delicate skin appears to be very sensitive to damage from ultraviolet radiation (Blaustein et al. 1995, Blaustein et al. 1996, Reavill 2001).There is evidence that different species have interesting adaptations to cope with exposure to varying amounts of ultraviolet radiation in nature. A nocturnal species of house gecko, Hemidactylus turcicus, has been demonstrated to be able to utilize relatively low levels of UV-B light. This suggests that perhaps their crepuscular basking habits allow them to obtain UV-B light during dawn and dusk hours (Carman et al. 2000). This has also been demonstrated in a species of anole, Anolis lineotopus which is diurnal but prefers shade to sun (Ferguson et al. 2005). Perhaps even more interesting is evidence suggesting that some species may select to bask in UV-B light to regulate vitamin D3 production (Ferguson et al. 2005).There is plenty of ongoing research in this area, and researchers are slowly working out more accurate requirements for UV provision in captivity (Acierno et al. 2006, Acierno et al. 2008, AZA Snake TAG 2011, Ferguson et al. 2010, Hedley and Eatwell 2013, MacCargar 2009, Oonincx et al. 2010, Rossi 2003).
5. Select a bulb according to the animal you have, and the type of enclosure you are using.
   1. Linear fluorescents are suitable for enclosures with a lot of floor space, as well as for long animals that have a large body area that needs UV exposure.
   2. Compact fluorescents are limited in their “spread” (orient them horizontally towards the basking area, to increase surface area exposed) but have a greater relative irradiance closer to the bulb, so they are more suitable for small enclosures.
   3. Mercury vapour lamps (flood or spot bulbs) are only suitable for very large enclosures. They produce a fair amount of heat as well as visible light, UVA and UVB (Baines et al. 2009).
6. The UV output of a bulb decreases over time, even if it is still producing visible light (Klaphake et al. 2003). If you have access to a UV-B radiometer (e.g. Solarmeter), regularly check the output of the bulb. It has been recommended that once the bulb drops to 70% of its original output, to replace it (Solartech Inc. 2014). If you do not have access to a radiometer (which is a completely reasonable assumption considering their cost), replace the bulb every 6-12 months, or according to the manufacturer’s recommendations.
7. Even though the UVB output on the package is relative, consider using “high output” bulbs (with an 8.0 or 10.0 rating) with species that would be exposed to a lot of UV light or in large enclosures, and mid-range output bulbs (5.0) with other species or in smaller enclosures. Low output bulbs (2.0) are probably not very useful in terms of UVB output.
8. 

   Would you have noticed the subtle early signs of NSHP in this Leopard Gecko (Eublepharis macularius)? The owners certainly didn’t.

   It never hurts to do some research on the species that you are keeping to see what has worked for other hobbyists. Books, journals, the Internet, herpetological societies, and your exotic veterinarian are all valuable resources. Always keep in mind that what has worked in one situation may not work in yours, and that sometimes hobbyists will divulge selective information about their successes and not their failures (which is arguably more valuable information). Learning more about your companion animal’s physiology will help you to better decide on which information is the most useful, and how to weed out less useful or just plain bad advice.

*Next Christina Discusses Metabolic Bone Disease in Reptiles | Treatment

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