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OK, Merlin said it best!
If you care for the "science" behind it I would refer you to Dr. Bernard's (et.al) study on Iguanas and D3 metabolism.
Idiosyncrasies of Vitamin D Metabolism in the Green Iguana (Iguana iguana)
JB Bernard[1], OT Oftedal[2], DE Ullrey[3]. Proceedings, Comparative Nutrition Society Symposium, pp. 11-14
In the study they injected D3 and fed D3 to iguanas while depriving them of UVB exposure. The results showed that the iguanas were unable to maintain proper 25-hydroxyvitamin D level in their blood.
So, the short answer is no, D3 drops cannot be used as a substitute for UVB exposure.
A portion of the study follows:
"The iguanas on Project 1 demonstrated a serum response in 25-hydroxyvitamin D to both forms of injectable cholecalciferol. It appeared that the injection in the emulsified base produced a higher response in serum 25-hydroxyvitamin D concentrations and sustained elevated serum concentrations of this vitamin D metabolite for a longer period. Each injected dose was roughly equivalent to the total amount of cholecalciferol an iguana would consume in a diet containing 2,000 IU/kg in a 5-month period. Yet, serum concentrations were still significantly lower than those attained by exposure to UV light. The percentage of 2096 phosphor was a significant factor in producing elevated levels of 25-hydroxyvitamin D in animals exposed to experimental lamps, with higher concentrations of this vitamin D metabolite associated with higher percentages of the phosphor. Serum concentrations of 25-hydroxyvitamin D in all animals exposed to the 2096 phosphor were maintained consistently in excess of 200 ng/ml, and ranged as high as 1,200 ng/ml.
In Project 2, all dosed animals exhibited a serum response to the oral cholecalciferol. The peak response in the absorption curve to this oral dose may have been missed due to the intervals between blood collections. However, by day 21 serum concentrations of 25-hydroxyvitamin D in the orally dosed iguanas already were on the decline. The amount of cholecalciferol administered to each animal (8.5 IU/g BW) was an extremely high dose, yet, serum concentrations of 25-hydroxyvitamin D were significantly lower than those attained by exposure to UV radiation. Serum concentrations of 25-hydroxyvitamin D in all animals exposed to the Experimental Reptile Light rose relatively rapidly, and were maintained after day 21 in excess of 330 ng/ml, ranging as high as 575 ng/mI.Serum concentrations of 25-hydroxyvitamin D of the magnitude seen in these projects have not been reported in other species, but concentrations previously reported in captive green iguanas housed outdoors were > 400 ng/ml (Allen et al., 1994). There may be several potential problems associated with highly elevated serum concentrations of vitamin D metabolites. In those species which have been studied, concentrations such as those seen here, might be associated with pathology. However, no clinical signs or radiographic evidence of vitamin D toxicity were seen in these iguanas."
So, there you have it in a nutshell! If D3 drops worked, lighting manufacturer's would not continue to spend so much money on reptile lighting development.
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Regards,
Dominick
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"Do you watch too much television? Did you do so as a toddler? Evidence tonight that it could be the cause of learning disorders, like attention deficit and hyperact-Ooooh, a kitty!" - Keith Olbermann
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