Animals need a variety of nutrients to meet their basic needs. These nutrients include fats and carbohydrates that provide energy, proteins that furnish amino acids, vitamins that serve as co-factors for enzymes and perform other functions, ions required for water balance and for nerve and muscle function, and selected elements that are incorporated into certain molecules synthesized by cells.

Once food is ingested, it is processed in an alimentary canal that begins at the mouth and ends at the anus. Food processing frequently begins with tearing or chewing action by a beak, teeth, or other mouth parts. Among animal species, there is a strong correlation between the size and shape of mouth parts and their function in capturing and processing food.

Chemical digestion of food also begins in the mouth. A salivary enzyme called alpha-amylase hydrolyzes the bonds linking glucose monomers in starch, glycogen, and other carbohydrates. Once food is swallowed, it passes down the esophagus via peristalsis. Digestion continues in the stomach, where a highly acidic environment denatures proteins and the enzyme pepsin begins the cleavage of peptide bonds linking amino acids.

External links

• The Federation of Animal Science Societies (FASS)
• National Institute of Animal Nutrition and Physiology (NIANP)
• Animal Nutrition Association
• Animal Nutrition Society of India (ANSI)