I am not advocating the elimination of beta-carotene from a gut-load diet. Regarding its value as a vitamin A precursor ..... well, you can decide when the "proof" threshold has been satisfied, if ever.
In 2002-2003, we included generous amounts of ground carrots in our gutloads. We still do. In 2003 we had accumulated a statistically significant number of visual observations suspected to be hypovitaminosis (insufficient) A. We considered other causitive agents as well. Our continued diagnosis and treatment eliminated all other causitive agents that we could think of, and the addition of real Vitamin A into the diet caused the symptoms to disappear in over 90% of the specimens. We have since accumulated data on over 100 chameleons where beta-carotene was generous in the gut-load, hypovitaminosos A was observed, and then the symptoms remedied by the addition of real Vitamin A (pre-formed Vitamin A, such as retinal palmitate) to the diet, given orally directly to the chameleon. Our numerous attempts to administer vitamin A via gut-load have all been assessed as inadequate.
Absolute "proof" is a matter of opinion in all things supplemental. "Proof beyond a reasonable doubt" is a lower threshold. My opinion would be solidly that beta-carotene is an inadequate precursor for Vitamin A in the chameleon species that I have worked with, and would swear it with regard to pardalis. That beta-carotene as a gutload is an inadequate source of Vitamin A for chameleons is an opinion that has been independently arrived at by some of the biggest names in chameleon medicine and husbandry, beginning in the latter '90's, to include Abate, Stahl, Alfonso, and Ferguson. Hope that helps.
