UVB exposure and therefore a stronger UVB bulb, while more temperate, or forest species require a lower UVB exposure and therefore a weaker bulb. These principles would hold true in open‐topped enclosures without a lid or when the bulb is placed inside the enclosure. However as mentioned previously, when the bulb is placed atop a screen, it can block a significant portion of the UVB reaching the animal. Therefore the author recommends selecting a bulb not simply based on the species but rather a combination of the species and the specific enclosure set‐up for the particular animal. There have been some cases in which animals where overexposed to UVB due to manufacturing errors in some UVB bulbs. As a consequence, some people believe that 10.0 bulbs are too strong and harmful for reptiles. This is not the case. In fact, it is difficult to replicate the natural UVB exposure from the sun and most bulbs cannot replace natural sunlight. It is rather the erroneous use of UVB bulbs that can lead to problems. Even a 2.0 bulb could cause problems if the reptile is allowed to come in direct contact with the bulb, as this is not the intended use. Buying a UVB bulb from a reputable manufacturer that provides clear guidance as to how to use the bulbs is the first step in the safe use of UVB bulbs. The second aspect is ensuring that the owners and caretakers are indeed using the bulbs in the safest, most efficient manner for the particular species.
MEASURING UVB
Another challenge in selecting the proper UVB bulb is the fact that bulb strength or percentage UVB emission does not directly translate to its effectiveness in stimulating vitamin D3 synthesis in the body. There are in vitro models to assess the efficiency of UVB light (Burger et al, 2007) but these are impractical in a clinical setting. We must rely on the reputation of the manufacturer to ensure the bulb is of good enough quality. How much UVB a particular reptile species requires is another question, without a clear answer. In general terms, reptiles should have exposure to a minimum of 13–20 μW/cm2 UVB irradiance with tropical species needing as much as 30–40 μW/cm2, and desert species requiring as much as 150 μW/cm2. Much research is needed to confirm this information, but it is a starting reference point. In nature, UVB exposure will vary with time of day, cloud covering, and so on, but in captivity the exposure level will be fairly constant while the bulb is turned on. Providing hiding places and a gradient of UVB light can help to reduce UVB overexposure although in practice overexposure is not as common of an event.
One practical option is to measure the UVB irradiance using a hand‐held radiometer. While expensive (approximately $250.00) these units are available to the general public. Their accuracy has been questioned, but they remain a good tool for the average reptile owner. A radiometer can be used to measure UVB irradiance of a bulb at any distance to determine how much UVB is being emitted and to record the decay of transmission over time. For example a 10.0 linear fluorescent bulb may emit 50 μW/cm2 at 12 inches when first purchased but after 6 months, the irradiance at 12 inches may have decreased to 25 μW/cm2. While this may still be acceptable exposure, it certainly indicates decrease in the bulb’s effectiveness over time. This decay is normal but if one desires to provide a more constant UVB exposure year round, it may be time to purchase a new bulb. They can also be used to evaluate the effect of the screen or mesh cover on the effectiveness of a bulb to help clients select the most appropriate bulb for their set‐up. Some newer radiometers measure ultraviolet index providing scale from minimum to very high while others provide readout based on the Ferguson zones to help determine the UVB exposure. These radiometers are advertised as being able to measure the appropriate UVB dose for vitamin D3 synthesis although that claim has not been verified.
CALCIUM SUPPLEMENTATION
All animals need a source of calcium and a calcium to phosphorus ratio of 1.5 : 2. Carnivorous animals eating adult whole prey items have the advantage of obtaining calcium form the prey’s bones. However herbivorous and omnivorous reptiles often lack an appropriate source of calcium. Young carnivores being fed immature prey items or carnivores not being offered whole prey items should also be supplemented with calcium. Most plant materials and invertebrates have a negative calcium to phosphorus ratio, so animals must find other sources of calcium. In their natural environment, these animals will travel to clay and mineral deposits or select particular feedstuffs to supplement their calcium intake. In captivity, reptiles do not have the opportunity to seek calcium sources but rather rely on it being supplemented in their diet. All herbivorous, omnivorous, and insectivorous reptiles require calcium supplementation.
Various commercial sources of calcium are available, but some are better than others. First off, it is recommended that calcium supplements be purely calcium with no phosphorus or vitamin D3. While many see a benefit of adding a D3 supplement, there are serious and real concerns about over supplementation of vitamin D3. Adding a calcium supplement that also contains phosphorus does not make sense because the reptiles are already in a negative calcium to phosphorus imbalance. Adding more phosphorus would not help solve this imbalance in an effective manner. The author prefers calcium only supplements including calcium powders sold for reptiles, cuttle bones, and crushed oyster shells. Another alternative is the use of fruit‐flavored calcium carbonate antacid tablets. These tables are more palatable than other products. They can be pulverized or fed in small pieces.
Regardless of the type of supplement, calcium is best offered daily to account for variations in intake. The supplement is mixed with the vegetables or by coating prey items. However, it must be noted that when insects are coated with a powdered supplement, the powder will fall off within 10–20 minutes. Insects should therefore be dusted immediately before feeding. There are some products that advertise calcium in a spray or gel cubes. These have not been proven to be effective and should be avoided until research to support their effectiveness is available. There are also some multivitamin products advertised for reptiles, and many of these include calcium as well as D3. Given that we do not know the nutritional requirement of most reptile species, the use of multivitamins is questionable. While it may be beneficial in some species it could be detrimental in others that may be over supplemented by certain minerals or vitamins. Finally, earthworms and hornworms (Manduca sp.) are two excellent sources of nutrition for carnivores and invertebrates because they tend to have a positive calcium to phosphorus ratio. However, this ratio can also vary with the conditions in which they are reared and maintained.
SUMMARY
All this information can be overwhelming to veterinarians and clients alike. It is important to understand the basics of UVB requirements and the factors that affect UVB supplementation. All six factors must be considered when selecting a bulb, as there is no single best bulb for every situation. There are new studies and product available every year, so it is also important to stay current on the literature and technological advances in order to provide better recommendations to clients. Proper calcium supplementation together with UVB light exposure is critical to prevent secondary nutritional hyperparathyroidism. The absence of either or both of these elements from the history of a reptile’s case should prompt veterinarians to include nutritional secondary hyperparathyroidism as a differential diagnosis.
GENERAL RECOMMENDATIONS FOR UVB LIGHTING IN REPTILE ENCLOSURES
For open‐topped enclosures or when there is no material between the bulb and the animal:
1 Use a T8 5–12% bulb at distances up to 15 inches between the bulb and the animal; for distances over 15 inches, a T8 12–14% or T5 10% bulb may be required.
2 Provide a UVB and heat gradient with the UVB bulb covering one‐third to three‐quarters of the cage length/depth.
3 Turn UVB light on for 10–12–hours daily.
For enclosures with a screen/mesh between the bulb and the animal:
1 Use a T8 10–12% bulb at distances up to 15 inches between the bulb and the animal; for distances over 15 inches, a T8 12–14% or T5
