ANN-0096
QUESTION
Tryptophan cannot be converted to niacin in: (a) Cats (b) Chickens (c) Ducks (d) Pigs?
OPTIONS
(A) (b) and (c) only
(B) (c) and (d) only
(C) (a) only
(D) (d) only
ANSWER
(C) (a) only
EXPLANATION
Cats cannot convert tryptophan to niacin (vitamin B₃) because they have very limited/absent activity of the enzymes required for the tryptophan → niacin pathway, particularly kynureninase. Therefore, cats have an absolute dietary requirement for preformed niacin. In contrast, chickens, ducks, and pigs can synthesize niacin from tryptophan, although the efficiency of conversion varies among species. Hence, only cats are unable to convert tryptophan to niacin among the options given.