or wire mesh top to keep the animals from escaping. Some of these screens may reduce the UVB light exposure to the animal by as much as 50%. To put this in perspective, if a reptile had a 5% linear fluorescent bulb, the effectiveness of that bulb might be reduced to that of a 2.5% by the time the light passes the screen and reaches the animal. This is why knowing the type of screen material is critical when selecting a bulb. A general recommendation is to select a screen with the largest aperture possible and with a mat or painted finish that will reflect less light.
SELECTING BULBS BASED ON SPECIES
There is a common trend toward make recommendations of bulbs based on the species with which it will be used. The principle behind this makes sense but in practice it is flawed. The thought is that certain species require higher UVB exposure and therefore a stronger UVB bulb while others require a lower UVB exposure and therefore a weaker bulb according to their biology and behavior. 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. The author therefore recommends selecting a bulb not simply based on the species but rather a combination of the species and the specific enclosure setup of the particular animal. Buying a UVB bulb from a reputable manufacturer that provides clear guidance as to how to use the bulbs is the first step in 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 that the bulb is of good enough quality. How much UVB a particular amphibian species requires is unknown at this time. 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 for amphibians. An additional consideration is to only turn the UVB lights on for 2–4 hours of daily or every other day exposure.
Radiometers
UVB irradiance cab be measured 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. 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 5% linear fluorescent bulb may emit 25 μW/cm2 at 12 inches when first purchased but, after 6 months, the irradiance at 12 inches may have decreased to 12 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 setup. 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. Most amphibians should be exposed to a Ferguson zone of 1 or 2 maximum and no higher.
CALCIUM SUPPLEMENTATION
All animals need a source of calcium and a calcium to phosphorus ratio of 1.5 : 2. Most invertebrates have a negative calcium to phosphorus ratio, so animals must find other sources of calcium. In their natural environment, these animals will seek out mineral deposits or particular feedstuffs to supplement their calcium intake. In captivity, amphibians do not have the opportunity to seek calcium sources but rather rely on it being supplemented in their diet. Various commercial sources of calcium are available, but some are better than others. First, 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 oversupplementation of vitamin D3. Adding a calcium supplement that also contains phosphorus does not make sense because the amphibians 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 can be provided by coating prey items. However, it must be noted that when insects are coated with a powdered supplement, it 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 reptile and many of these include calcium as well as D3. Given that we do not know the nutritional requirement of most amphibian 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 spp.) are two excellent sources of nutrition 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 up to date with the literature and technological advances 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 an amphibian case should prompt veterinarians to include secondary nutritional hyperparathyroidism as a differential diagnosis.
GENERAL RECOMMENDATIONS FOR UVB LIGHTING IN AMPHIBIAN ENCLOSURES
A. For open top enclosures or when there is no material between the bulb and the animal:
1 Use a T8 2–6% bulb at distances up to 15 inches between the bulb and the animal; for distances over 15 inches, a T8 10–12% or T5 6% bulb may be required.
2 Provide a UVB and heat gradient so animals are not constantly exposed to UVB light.
3 Turn UVB light on for 2–4 hours daily to every other day, especially for cryptic or fossorial species that are naturally exposed to low levels of UVB.
For enclosures with a screen/mesh between the bulb and the animal:
1 Use a T8 6–12% bulb at distances up to 15 inches between the bulb and the animal; for distances over 15 inches, a T8 12% or T5 6% bulb may be required.
2 Provide a UVB and heat gradient so animals are not constantly exposed to UVB light.
3 Turn
