<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (March 2018) (Learn how and when to remove this template message) </Td> </Tr> <P> Animal nutrition focuses on the dietary needs of animals, primarily those in agriculture and food production, but also in zoos, aquariums, and wildlife management . </P> <P> There are seven major classes of nutrients: carbohydrates, fats, fibre, minerals, proteins, vitamins, and water . </P> <P> Macronutrients (excluding fiber and water) provide structural material (amino acids from which proteins are built, and lipids from which cell membranes and some signaling molecules are built) and energy . Some of the structural material can be used to generate energy internally, though the net energy depends on such factors as absorption and digestive effort, which vary substantially from instance to instance . Vitamins, minerals, fiber, and water do not provide energy, but are required for other reasons . A third class dietary material, fiber (i.e., non-digestible material such as cellulose), seems also to be required, for both mechanical and biochemical reasons, though the exact reasons remain unclear . </P>

Which of the following is the only animal category that contains significant amounts of carbohydrate