Digestion and Genetics in Animal Science

DIGESTION

The Gastrointestinal Tract

  • Digestion involves both physical and chemical changes that feed undergo in the gastrointestinal tract and the release of nutrients for absorption.

Classification of Digestive Systems

What They Eat

  1. Omnivore

    • Definition: Animals that eat both animal and vegetable materials.

    • Examples: Chicken, pigs, humans, and dogs.

  2. Carnivore

    • Definition: Flesh-eating animals.

    • Examples: Cats or birds of prey.

  3. Herbivore

    • Definition: Animals that primarily consume vegetable or plant-based feeds, often with the help of cellular leases.

    • Examples: Horses, cows, rabbits, guinea pigs, and elephants.

Cellular Lesions

  • Definition: Enzymes produced by bacteria that live in the gastrointestinal tract.

Bacterial Fermentation

  • Definition: The process of bacteria utilizing plants, breaking down and consuming plant material.

Digestive Tract Types

  1. Monogastric

    • Definition: A simple digestive system, or a complicated digestive tract with a cecum.

    • Examples: Mink, dogs, and cats have simple digestive tracts.

  2. Cecum

    • Definition: The region where bacterial fermentation occurs.

    • Special Note: Horses and rabbits have cecal fermentation, allowing them to consume lots of plant material.

  3. Ruminant

    • Definition: Animals with a complex digestive tract divided into multiple compartments.

    • Ruminant examples: Cattle, sheep, and goats.

  4. Rumen

    • Definition: A four-compartment structure in ruminants that facilitates complicated fermentation, particularly for high fibrous feed consisting of indigestible carbohydrates.

Digestive Facts

  • The type of digestive system dictates what food an animal can consume;

  • Complicated feeds, like forage feed, require more complex digestive tracts.

  • Ruminants, such as sheep, can retain feed for up to 7 days.

Terminology

  1. Enzymes

    • Definition: Organic catalysts that promote biochemical changes and facilitate reactions.

    • Composition: Proteins composed of amino acids.

    • Function: Break down chains to prepare them for absorption into the bloodstream.

  2. Absorption

    • Definition: The process of nutrients released during digestion passing through the intestinal wall into the circulatory system.

  3. Metabolism

    • Definition: The process of utilizing carbohydrates (CHO) and fats for energy; recombining amino acids to form proteins, hormones, and enzymes.

    • Ration utilization requires going through digestion, absorption, circulation, and cellular metabolism.

Steps Involved in Digestion

  1. Prehension (Gathering of food)

    • Mechanism: Involves lips, tongue, and teeth.

    • Note: Ruminants lack upper incisor teeth.

  2. Mastication (Mechanical breakdown)

    • Process: Vertical and lateral movement of jaws and teeth to crush food.

    • Importance: Increases surface area for further digestion.

    • Ruminants engage in rumination (40-50,000 times/day) and form bolus (globs of food).

  3. Saliva Secretion

    • Functions:

      • Lubricates food to ease chewing and swallowing.

      • Enhances taste sensation.

      • Acts as a solvent to dissolve food for taste bud contact.

    • Unique to ruminants: Their saliva contains bicarbonates that buffer acids produced by microorganisms in the rumen, preventing damage and preparing nutrients for the microorganisms.

  4. Deglutition

    • Definition: The act of swallowing, which occurs involuntarily and is controlled by neural responses.

    • Describes the peristaltic waves that move food through the esophagus.

  5. Complex Carbohydrate Fiber Digestion

    • Occurs post-deglutition in ruminants, facilitated by bacterial fermentation in the rumen.

    • Results in beneficial byproducts that the animal can digest and absorb.

  6. Stomach Function

    • Monogastrics: Involves stomach processing similar to birds' proventriculus.

    • Ruminants use the abomasum for physical and chemical breakdown.

      • Notable for producing HCl (denaturing proteins) aiding enzymes' action.

      • Enzymatic breakdown includes pepsin, renin, and lipase.

  7. Chyme Formation

    • Chyme: Acidic mixture formed in the stomach.

    • Mixed with alkaline secretions from the liver (bile) and pancreatic juices that contain various digestive enzymes.

    • Important enzymes: Trypsin, chymotrypsin, carboxy-peptidase, amino-peptidase, intestinal lipase, and amylase.

  8. Small Intestine Digestion

    • Comprises three parts:

      • Duodenum: Main site for food breakdown via bile and pancreatic secretions.

      • Jejunum: Absorption of nutrients.

      • Ileum: Completes absorption with nutrients passing into the lymphatic or circulatory system.

  9. Large Intestine Function

    • Absorption limitations due to lack of villi and enzyme production.

    • Comprising three parts:

      • Colon

      • Cecum: Varies functionality in species (e.g., monogastric herbivores have lower absorption capability).

      • Rectum

Digestive Process in Pigs

  • Pigs are omnivorous and monogastric.

    • Unique: Salivary amylase is secreted, beginning starch breakdown but of little nutritional importance due to the acidic pH in the stomach.

    • Enzymes in gastric juices are as expected for monogastric animals.

    • Protein digestion completes in the intestine; most fat digestion occurs in the small intestine.

Pancreatic Juice Functions

  • Contains various enzymes aiding digestion.

  • Sodium carbonate and sodium bicarbonate neutralize stomach acid.

  • Pancreas produces insulin, essential for carbohydrate metabolism.

Bile Functions

  • Aids in the digestion and absorption of fats and fat-soluble vitamins.

Digestion in Ruminants

  • Involves a complex structure, including an abomasum (stomach) adapted for digesting roughage (fiber/cellulose).

  • Microorganisms in the rumen ferment feed, producing essential nutrients.

  • Ruminants quickly fill the rumen without chewing, resting before chewing cud.

  • Complex rumen comprises four compartments:

    1. Rumen

    2. Reticulum

    3. Omasum

    4. Abomasum

Rumen Functions

  • Acts as an anaerobic bacterial fermentation site, stores food until the animal can chew it.

  • Bacteria digest carbohydrates such as cellulose and starch, producing volatile fatty acids (VFAs) as energy sources, protein, and gas, which is released via eructation.

Reticulum Functions

  • Ensures proper fermentation dynamics as the pacemaker for rumen contractions, facilitating mixing.

Omasum Functions

  • Absorbs water, electrolytes, and VFAs, while reducing particle size of digest food.

Benefits of Microbial Fermentation

  • Microorganisms synthesize protein and even convert non-protein nitrogen into a protein source.

  • They also help in the absorption of vitamins and energy production.

Eructation Mechanism in Ruminants

  • Critical for removing gases produced during fermentation.

  • Gas must be belched out as it enters the lungs and is exhaled.

  • The sound produced can often be muffled.

Volatile Fatty Acids Produced

  • Major fermentation products include:

    • Acetate, propionate, butyrate, isobutyrate, valerate, and isovalerate.

  • VFAs can fulfill about 50-70% of the total energy needs of ruminants.

Digestion in the Avian Species

Gizzard Functions

  • Grinding organ that relies on secretions from the proventriculus.

Avian Digestion Unique Features

  • Structure lacks teeth, and utilizes the crop for storage and food moistening.

Cecal Digestion in Birds

  • Two ceca located near the junction of the small and large intestines, size is influenced by the type of diet.

  • The large intestine is relatively short.

Horse Information

  • Nonruminant herbivore capable of utilizing roughage.

  • Prehension is facilitated by a flexible upper lip, teeth, and tongue.

  • Saliva contains no enzymes but is essential for lubrication.

Equine Digestion

  • Characterized by vertical and lateral jaw movements, producing large amounts of saliva (up to 10 gallons per day).

  • Utilizes one-way peristalsis.

Disadvantages of Horse Digestion

  • Fermentation may decrease the quality of high quality feeds, requiring considerable energy.

  • The presence of a smaller stomach capacity increases susceptibility to disorders.

Digestion in the Horse

  • The large intestine accounts for over 60% of gut capacity, divided into cecum, large colon, small colon, and rectum.

  • Bacterial populations in the cecum enable fermentation, providing energy from volatile fatty acids back to the horse.

Fiber Digestion in Horses

  • Soluble carbohydrates digest and absorb in the small intestine, while fiber is fermented in the large intestine; however, the process is less effective than in ruminants.

Plants in Animal Feed

  1. Cereal Grains (e.g., wheat, rye, sorghum, barley, oats, corn)

    • High in energy.

  2. Silage

    • Preserved plant material; microbial growth occurs post-harvest.

    • Corn silage is commonly used.

  3. Legumes (e.g., soybeans, alfalfa)

    • High protein content.

  4. Grasses (e.g., timothy, rye, fescue)

    • Fresh (pasture) or preserved (hay).

Feedstuff Categories

  1. Dry Forages and Roughages

    • Typically contain at least 18% crude fiber.

  2. Pasture, Range Plants, and Green Forages

    • Variability in moisture content affects nutritional quality.

  3. Silages

    • A common storage method produced via anaerobic fermentation.

  4. Energy Feeds

    • Contains less than 18% crude fiber and under 20% protein.

  5. Protein Supplements

    • Inclusion of plant or animal origin or non-protein nitrogen sources.

  6. Mineral and Vitamin Supplements

    • Needed for balancing rations; specific examples include calcium carbonate or salt.

  7. Nonnutritive Additives

    • Various ingredients added for purposes beyond nutrition, such as antibiotics and growth stimulants.

Genetics and Breeding

Definitions

  • Genetics: The study of heredity and transmission of traits from parents to offspring.

  • Genotype: The genetic makeup; expressed phenotype is observable traits.

Chromosome Structure

  • Composed of DNA and is found in pairs.

  • Genes: Sequences along chromosomes that define traits.

DNA Characteristics

  • Comprised of nucleotides; vital for encoding genetic information.

  • DNA Replication: Process of DNA duplicating itself before cell division.

Inheritance Principles

  • Mitosis: Somatic cell division producing two identical diploid cells.

  • Meiosis: Gametogenic process producing haploid gametes, involves reduction division.

Female Reproductive Physiology

  1. Ovaries: Site of oocyte storage and hormone production.

  2. Oviduct: Transport medium where fertilization occurs.

  3. Uterus: Passage for sperm; supports fetal development.

  4. Cervix: Acts as a barrier and storage for sperm.

  5. Vagina: Expels fetus and serves as the copulatory organ.

Regulation of Reproductive Hormones

  • Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) signal ovum development and ovulation.

  • Corpus luteum (CL) forms post-ovulation, secreting progesterone to maintain pregnancy.

Parturition

  • Hormonal initiation of birthing process, resulting in the expulsion of the fetus and membranes.

Environmental Factors Affecting Reproduction

  • Nutritional status, energy availability, and other stress factors have marked impacts on reproductive mechanisms and efficiency.

Conclusion

  • Understanding digestion and genetics, along with how these systems function in various animal species, is essential for effective animal nutrition and breeding practices. This knowledge is crucial for improving animal health and productivity in agricultural practices.