Axenic animals have lower requirements for Vitamin A; which statement reflects this?

• A. It is required in lower amounts.
• B. It is not required at all.
• C. It must be supplemented daily.
• D. It is harmful if given.

Answer: (A)

Axenic animals lack the gut microbes that normally interact with the host’s metabolism and immune system, which can influence how much of certain nutrients the body needs. For Vitamin A, the presence of gut microbes and the immune activity they drive can increase the host’s baseline use and requirement of this nutrient to maintain mucosal surfaces and support immune function. Without those microbial influences, the animal’s need for Vitamin A is reduced, so a statement describing the requirement as lower best fits. Vitamin A remains an essential nutrient, so it is not accurate to say it’s not required at all or that it must be supplemented on a fixed daily schedule regardless of status. It’s not inherently harmful to give Vitamin A, but the point of the question is about the relative level of requirement, which is reduced in axenic conditions.