Ferrets (Mustela putoius furo) Inefficiently Convert β-Carotene to Vitamin A

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Abstract
The ferret has recently been used as a model to evaluate the absorption and metabolism of several carotenoids; however, little is known about the vitamin A (VA) requirements of this species or the ability of ferrets to convert dietary β-carotene (βC) to VA. Three studies were conducted to estimate the daily utilization of VA in ferrets and to determine the effect of prior VA status on the ability of ferrets to utilize βC as a source of VA. Weanling male ferrets were fed a pelleted, low carotenoid, semipurified diet either with (+VA) or without VA (−VA) for 21- to 35-d prefeeding periods. Upon initiation of the experiments, several ferrets were killed to determine base-line VA status. The remaining ferrets were fed VA, βC, or VA and βC in pelleted feed (Studies 1–3) or liquid carrier (Study 3) for 16–21 additional days. Hepatic VA and βC concentrations were used as the primary indicators of VA status, although serum and adrenal VA and βC also were measured. The results showed the following: 1) provision of βC at up to a 15:1 weight ratio of βC to VA in pelleted feed or liquid carrier was not sufficient to maintain hepatic VA stores after a −VA prefeeding period; 2) the daily utilization rate of VA by ferrets ranged from 80 to 171 μg in the three studies; 3) the ferret was confirmed to be a species that has the majority of its serum VA in ester form; and 4) feeding −VA diets significantly reduced serum retinyl esters but had less effect on serum retinol. We conclude that although ferrets can convert βC to VA, the process is inefficient. The ferret model can be most appropriately used when studying the biological effect of tissue βC stores on VA status and is less appropriate for the evaluation of dietary βC conversion to VA.