Digestive System of Animals Animal Science Frameworks

Presentation Unit 3.1

Mr. Sullivan

Digestion

Purpose: reduce feed particles to molecules that can be absorbed into the blood

• Mechanical breakdown of food– chewing

• Chemical breakdown of food– HCl in the stomach– enzymes

• Contractions of digestive tract

Animals are classified by the types of food they ingest

• Carnivore - animal products– Dogs, Cats

• Herbivore - plant products– Cattle, Sheep, Goats, Horses

• Omnivore - combination of plant and animal products– humans, pigs

Animals are also classified by the type of stomach they have

• Monogastrics or non-ruminants

• Ruminants

Monogastric Animals

Monogastric – one or simple stomach structure

• mostly carnivores and omnivores» Very simple: mink and dog» Cecal digestion: horse, rabbit or rat» Sacculated stomach : kangaroo

Ruminant Animals

Ruminant - 4 compartment stomach with the compartments before the “true” stomach

• herbivores» cattle, sheep, goats and pseudoruminants (llamas)

Digestion

• Prehension– Bringing the food to the mouth

• Upper limbs, head, beak, claws, mouth, teeth and lips

• Mastication or chewing– To crush the food, increase surface area and

allow enzymes to act on molecules• Carnivores need only to reduce the size of the particle• Herbivores must chew continuously (40-50,000 times

a day)

Monogastric Animal Digestive Tract

Basic anatomymouth

stomach

small intestine

large intestine or colon

Monogastric Animal Digestive Tract

• Feed passes from the mouth to the stomach through the esophagus

• To reduce the size of the feed particles

• From the stomach it passes through the– duodenum (first part of the small intestine)

• Bile and pancreatic secretions enter here

– jejunum (second part of the small intestine)• Absorption of nutrients

– ileum (third part of the small intestine)• To split food molecules and absorb nutrients

Monogastric Animal Digestive Tract

• Large Intestine• water absorption• feces formation

• Rectum

Human and Pig Similarities

• Both are omnivores

• Cannot synthesize B complex vitamins

• Cannot synthesize amino acids

• Can become obese with increased food intake

Monogastric Animal Digestive Tract

• Exceptions– herbivores

• horses have a cecum (blind anterior end of the colon) where feed is fermented

– Cecum is posterior to optimum feed absorption area, thus advantages of the ruminant animal is lost

Enzymes of the Digestive Tract

Enzyme names often end in -ase

and

begin with a description of the substrate they act upon

Enzymes of the Digestive Tract

Enzyme Substrate Product

Amylase Starch Dextrin, Disaccharides

Chymotrypsin Peptides Amino Acid

Peptides

Lactase Lactose Glucose

galactose

Enzymes of the Digestive Tract

Enzyme Substrate Product

Lipase Lipids Fatty acids glycerides

Pepsin Protein polypeptide

Peptidase Peptides amino acid

Sucrase Sucrose glucose

Trypsin Protein polypeptide

Monogastric Digestion

• Enzymes help breakdown large molecules– Mouth

• amylase in saliva of humans and pigs breaks down starch to disaccharides and dextrin

– Stomach• HCl - creates acidic environment• pepsin - breaks proteins down polypeptides

Monogastric Digestion

• Enzymes help breakdown large molecules– duodenum

• Cells release hormones that act on pancreas and gall bladder

– secretin– pancreozymin– cholecystokinin

Monogastric Digestion

• pancreas– lipase

• lipids to fatty acids and glycerides

– trypsin• proteins to polypeptides

– chymotrypsin• peptides to amino acids and peptides

– amylase• starch to disaccharides and dextrin

Monogastric Digestion

• gall bladder– bile

• produced in the liver• emulsifies fats• alkaline to neutralize stomach contents that are

acidic

• small intestine– amino acids, fatty acids and monosaccharides

are available for absorption

Ruminant Digestion

• mouth

• esophagus

• rumen

• reticulum

• omasum

• abomasum

• small intestine

• large intestine

Ruminant Digestion

• rumen - 40 gallons in a cow– large fermentation vat– covered with papillae to increase the surface

area– microorganisms digest cellulose – microorganisms synthesize amino acids from

nonprotein nitrogen – microorganisms synthesize B-complex

vitamins

Ruminant Digestion

• reticulum - 2 gallons in a cow– lining looks like a honeycomb– interacts with rumen to mix contents

Ruminant Digestion

• omasum - 4 gallons in a cow– many folds, perhaps to grind feed

Ruminant Digestion

• abomasum - 4 gallons in a cow– true stomach

Ruminant Digestion

• Ruminants eat forage rapidly– they regurgitate food (cud) – and chew it again and swallowed

• Rumination - continuous reguritation, chewing and swallowing

• Eructation - elimination of gases (methane and carbon dioxide) in the rumen from fermentation

Rumen Microorganisms

• Bacteria and Protozoa– rumen environment is moist, warm, and

provides a constant supply of nutrients– entire population of organisms depending on

the kind and quality of the feed– when they are washed out of the omasum into

the abomasum the acidic environment kills the microorganisms

– provide amino acids and some energy

Ruminant Digestion

• Ruminants to not secrete amylase in their saliva

• bacteria and protozoa in the rumen and reticulum utilize starches and sugars- no glucose available for the ruminant– microorganisms do produce volatile fatty acids

(VFA) that are absorbed and converted to energy

• acetic, propionic and butyric acids

• major source of energy

Energy Pathways in the Ruminant

From Rumen to Abomasum

Injestion materials

Cellulose Starch Fat

Complex Sugars

Glucose

VFAs

Energy Pathways in the Ruminant

Liver

VFAs

Glucose

Ruminant and Monogastric Absorption in the small intestine• passive transport

– diffusion by concentration

• active transport– villi engulf molecules

• to bloodstream or lymph system

Rumen Microorganisms

• Bacteria and Protozoa– rumen environment is moist, warm, and

provides a constant supply of nutrients– entire population of organisms depending on

the kind and quality of the feed– when they are washed out of the omasum into

the abomasum the acidic environment kills the microorganisms

– provide amino acids and some energy