Animal Nutrition Overview

Animal Nutrition Overview

• Animals are multicellular eukaryotic heterotrophs that ingest their food (organic matter from the environment).

• Nutrition is the process of acquiring and breaking down food.

Dietary Categories

• Animals are broadly categorized as herbivores, carnivores, or omnivores based on their food sources.
  • Herbivores primarily eat plants and algae.
  • Carnivores consume other animals.
  • Omnivores eat both plants/algae and animals.

Nutritional Needs

• A diet must supply chemical energy (ATP) for cellular processes, organic building blocks for macromolecules (e.g., carbohydrates, proteins, lipids), and essential nutrients (materials animals cannot synthesize and must obtain from their diet; include essential amino acids, essential fatty acids, vitamins, and minerals).

Food Processing: Ingestion

• Ingestion is the act of eating/feeding.
• Strategies vary greatly among animal species:
  • Suspension feeding: filter small food particles from water.
  • Substrate/deposit feeding: live in or on their food.
  • Fluid feeding: suck nutrient-rich fluids.
  • Bulk feeding: eat relatively large pieces of food; Most animals.

Food Processing: Digestion

• This is the process of breaking down food.
• Mechanical digestion physically breaks food into smaller pieces.
• Chemical digestion uses enzymes to break down complex food molecules into absorbable forms.
  • Intracellular digestion: occurs within the cells of single-celled organisms or simple animals; food enclosed in vacuoles, digested, and dissolved.
  • Extracellular digestion: occurs outside the cells of complex animals; takes place in compartments which allow for more efficient digestion.
    • Gastrovascular cavity: simple sac-like cavity in some simple animals; food is digested in the cavity, and nutrients are distributed throughout the body.
    • Alimentary canal (digestive tract): has two openings (mouth & anus). Food moves through several compartments undergoing digestion and absorption. Animals with more complex body plans typically have digestive systems organized in this way. This allows for compartmentalization with digestive processes taking place in distinct locations.
    • Examples:
      • Birds: lack teeth, but have a crop to store and soften food; and two stomachs (chemical and mechanical digestion in the gizzard).
      • Mammals: chewing aids digestion, saliva coats food; have dedicated digestive glands (salivary glands, pancreas, liver, gallbladder).
      • Adaptations among different animal types include specific stomachs(for example, ruminants, 4-chambered stomachs, rumen used in fermentation and storage) and specific adaptations of the intestine and teeth (various tooth types according to diet).
      • Bearded vultures: have extreme stomach acidity to allow digestion of bones.

Food Processing: Absorption

• Absorption is the uptake of digested nutrients from the digestive compartments to the body cells.
• Most absorption occurs in the small intestine which has increased surface area due to folds and villi.

Food Processing: Elimination

• Elimination is the release of undigested food waste (feces) from the body

Adaptations for Digestion

• Different animals have adaptations specialized for their diets (herbivores, carnivores, omnivores).
• Adaptations include: varied dental structures, modifications of stomach and intestinal structures, and mutualistic relationships (digestive processes involving other organisms, e.g. bacteria, often found in intestinal systems).