Animal Nutrition Notes

Chapter 41: Animal Nutrition

41.1 Dietary Needs

  • Animals need food for energy and essential nutrients for growth and reproduction.
  • An adequate diet must satisfy three nutritional needs:
    • Chemical energy.
    • Organic building blocks.
    • Essential nutrients.
  • Vitamins: Water-soluble vitamins are less likely to result in overdose compared to fat-soluble vitamins because they are not stored in the body.
  • Deficiency Disorders:
    • Beriberi:
      • Symptoms: nerve damage, heart failure.
      • Vitamin Deficient: Thiamin (B1).
    • Scurvy:
      • Symptoms: defective connective tissue.
      • Vitamin Deficient: Ascorbic Acid (Vitamin C).
    • Rickets:
      • Symptoms: bone deformities.
      • Vitamin Deficient: Vitamin D.
  • Mineral Requirements:
    • Calcium:
      • Major Functions/Deficiency Symptoms: Bone and tooth formation, nerve and muscle function / impaired growth, loss of bone mass.
    • Phosphorus:
      • Major Functions/Deficiency Symptoms: Bone and tooth formation, acid-base buffer / weakness, bone loss.
    • Sulfur:
      • Major Functions/Deficiency Symptoms: Component of certain amino acids / impaired growth.
    • Potassium:
      • Major Functions/Deficiency Symptoms: Nerve function, acid-base balance / muscular weakness, paralysis.
    • Chloride:
      • Major Functions/Deficiency Symptoms: Fluid balance, hydrochloric acid production / muscle cramps, reduced appetite.
    • Sodium:
      • Major Functions/Deficiency Symptoms: Fluid balance, nerve function / muscle cramps, reduced appetite.
    • Magnesium:
      • Major Functions/Deficiency Symptoms: Enzyme cofactor / nervous system disturbances.
    • Iron:
      • Major Functions/Deficiency Symptoms: Component of hemoglobin, enzyme cofactor / anemia, weakness.
    • Fluorine:
      • Major Functions/Deficiency Symptoms: Maintenance of tooth structure / higher frequency of tooth decay.
    • Iodine:
      • Major Functions/Deficiency Symptoms: Component of thyroid hormones / goiter (enlarged thyroid).
  • Malnutrition: Results from a long-term absence from the diet of one or more essential nutrients.
  • Undernutrition: Results from the diet not providing enough chemical energy.

41.2 Food Processing

  • Four Stages of Food Processing:
    • Ingestion: Eating or taking in food.
    • Digestion: Breaking down food into smaller molecules.
    • Absorption: Uptake of nutrients by cells.
    • Elimination: Passing of undigested material out of the body.
  • Four Main Feeding Mechanisms:
    • Suspension Feeders: Filter particles from water.
    • Substrate Feeders: Live in or on their food source.
    • Fluid Feeders: Suck nutrient-rich fluid from a living host.
    • Bulk Feeders: Eat relatively large pieces of food.
  • Mechanical Digestion: Physical breakdown of food.
  • Chemical Digestion: Chemical breakdown of food using enzymes.
  • Enzymatic Hydrolysis: Breaking bonds with the addition of water via enzymes.
  • Organic Molecules and Building Blocks:
    • Carbohydrates give rise to Monosaccharides.
    • Proteins give rise to Amino Acids.
    • Nucleic Acids give rise to Nucleotides.
    • Fats(lipids) give rise to Glycerol and Fatty Acids.
  • Nutrients from a recently ingested meal are not technically “inside” the body until they are absorbed across the intestinal lining into the bloodstream or lymphatic system.
  • Intracellular Digestion: Digestion within cells (e.g., food vacuoles in sponges).
  • Extracellular Digestion: Digestion outside of cells, in compartments (e.g., alimentary canal).
  • Alimentary Canal: A complete digestive tract, starting at the mouth and ending at the anus.

41.3 Mammalian Digestive System

  • Digestion begins in the oral cavity with mechanical (teeth) and chemical (saliva) digestion.

    • Mucus: Protects and lubricates.
    • Buffers: Neutralize acid to protect teeth.
    • Antimicrobial Agents: Kill bacteria.
    • Amylase: Breaks down starches and sugars.

  • Food is kept from entering the trachea by the epiglottis which blocks the glottis (the opening to the trachea) when swallowing.

  • Peristalsis: Rhythmic contractions of muscles in the wall of the alimentary canal that pushes food down; it begins in the esophagus.

  • Functions of the Stomach:

    • Stores food.
    • Secretes gastric juice, which mixes with the food.

  • Interior Surface of the Stomach:

    • Gastric Gland: Contains mucus, chief, and parietal cells.
    • Mucus Cells: Secrete mucus to protect the stomach lining.
    • Chief Cells: Secrete pepsinogen (inactive form of pepsin).
    • Parietal Cells: Secrete hydrochloric acid (HCl) which activates pepsinogen to pepsin.

  • Positive Feedback Loop in Gastric Juice Production:

    • Food stimulates the release of gastrin.
    • Gastrin stimulates the secretion of gastric juice.
    • Gastric juice helps digest proteins.
    • Partially digested proteins stimulate more gastrin release.

  • Pepsin functions in the stomach due to its specific tertiary structure, which is adapted to the acidic environment of the stomach. It would not function in the small intestine because the pH is different.

  • Digestive Function of the Liver: Produces bile.

  • Function of Bile: Emulsifies fats for easier digestion and absorption; stored in the gallbladder.

  • Two Digestive Functions of the Small Intestine:

    • Chemical digestion.
    • Nutrient absorption.

  • Enzymes Involved in Digestion:

    • Carbohydrates:
      • Oral Cavity: Salivary amylase (substrate: starch, product: smaller polysaccharides).
      • Lumen of Small Intestine (enzymes from Pancreas): Pancreatic amylases (substrate: polysaccharides, product: disaccharides).
      • Epithelium of Small Intestine: Disaccharidases (substrate: disaccharides, product: monosaccharides).
    • Proteins:
      • Stomach: Pepsin (substrate: proteins, product: small polypeptides).
      • Lumen of Small Intestine (enzymes from Pancreas): Trypsin and chymotrypsin (substrate: polypeptides, product: smaller polypeptides), carboxypeptidase (substrate: polypeptides, product: amino acids).
      • Epithelium of Small Intestine: Aminopeptidase, dipeptidase (substrate: small polypeptides, product: amino acids).
    • Nucleic Acids:
      • Lumen of Small Intestine (enzymes from Pancreas): Pancreatic nucleases (substrate: DNA and RNA, product: nucleotides).
      • Epithelium of Small Intestine: Nucleotidases (substrate: nucleotides, product: nucleosides), phosphatases (substrate: nucleosides, product: nitrogenous bases, sugars, phosphates).
    • Fats:
      • Lumen of Small Intestine (enzymes from Pancreas): Pancreatic lipase (substrate: fats (triglycerides), product: glycerol, fatty acids, monoglycerides).
        Fats are absorbed from the small intestines through these steps:
    1. Bile salts emulsify fat droplets into smaller particles.
    2. Lipase digests the fat droplets to glycerol, fatty acids, and monoglycerides.
    3. Monoglycerides and fatty acids are absorbed and converted back into triglycerides and form chylomicrons.
    4. Chylomicrons are transported into lacteals.
    5. Lacteals transport chylomicrons to larger veins.

41.4 Evolutionary Adaptations and Diet

  • Lacteals: Vessels of the lymphatic system that absorb fats. Found in the villi of the small intestine.
  • Cecum: A blind pouch at the junction of the small and large intestines. In grazing animals, it houses bacteria that help digest cellulose.
  • Appendix: Located near the junction of the small and large intestines in humans. It has a minor role in immunity.
  • Colon: Major function is to recover water from undigested material.
  • Mammalian Dentition and Diet:
    • Carnivores: Have large, pointed incisors and canines to kill prey, and jagged premolars and molars to crush and shred meat.
    • Herbivores: Have incisors and canines modified for biting off vegetation, and premolars and molars with broad, ridged surfaces for grinding plants.
    • Omnivores: Have teeth adapted for both meat and plant consumption.
  • Herbivores have longer alimentary canals than carnivores because plant matter is more difficult to digest than meat.
  • Mutualistic symbiotic bacteria in the colon (microbiome) aid in digestion by:
    • Breaking down materials that the host cannot.
    • Producing essential vitamins.
  • Stress does not directly cause ulcers. Ulcers are often caused by the bacterium Helicobacter pylori. The 2005 Nobel Prize was awarded to the scientists who discovered this.
  • Fecal Microbial Transplantation: Can restore a healthy microbiome by transferring fecal bacteria from a healthy individual to a patient suffering from intestinal infections.
  • Herbivores get energy from plant cellulose through mutualistic relationships with microorganisms that produce cellulose-digesting enzymes.

41.5 Feedback Circuits

  • Regulation of Digestion (Hormonal Feedback):
    • Positive Feedback: Presence of food stimulates release of digestive enzymes; partially digested proteins stimulate gastrin release.
  • Regulation of Energy Storage and Glucose Homeostasis:
    • Insulin: Released by the pancreas when blood glucose levels are high. Promotes the uptake of glucose by cells, lowering blood glucose level.
    • Glucagon: Released by the pancreas when blood glucose levels are low. Promotes the breakdown of glycogen to glucose in the liver, raising blood glucose levels. The synthesis and breakdown of glycogen are central not only to energy storage, but also to maintaining glucose homeostasis.