Digestive Systems Chris Ellason

Digestion and Absorption: 4 The process of digestion includes: –The prehension of food or feed –The mechanical chewing and grinding –Mixing with digestive acids and enzymes to chemically break down feedstuffs 4 The process of absorption includes: –Transport of the digested foods across the intestinal mucosa to the blood or lymph system

General Terms 4 Prehension: to take into the mouth 4 Mastication: chewing 4 Deglutition: swallowing 4 Regurgitation: the backward flow of food through the esophagus

Three Major Categories 4 Carnivore: consume flesh of other animals, examples are dogs and cats 4 Omnivore: consume both plants and flesh, examples are primates 4 Herbivore: consume plant material, examples are horses and cattle

Carnivore 4 Very Well developed stomach 4 Uncomplicated intestine 4 Limited fiber digestion

Omnivore 4 Combination of carnivores/herbivores 4 More complicated GIT than carnivores 4 Colonic digesters –Pigs, humans 4 Cecal digesters –rat

Herbivore 4 Cow, horse, rabbit –Each has a different type of GIT 4 Cow- ruminant 4 Horse- simple stomach, large cecum, large sacculated LI 4 Rabbit- larger stomach, very large sacculated cecum, unsacculated LI

Salivary Glands 4 3 pair –Parotid –Mandibular –Sublingual 4 Water - moistens food aids in swallowing 4 Mucin - lubrication for swallowing 4 Bicarbonate salts 4 Enzymes

Salivary Glands

Salivary glands

Different Digestive Tracts 4 Farm animals have a variety of digestive systems –Ruminants: have 4 different compartments to the stomach Examples include cattle, sheep, goats –Nonruminants (also known as monogastrics) Hogs, dogs, and cats have a single, simple stomach Poultry have a two part stomach Horses have a large, functional cecum

Pregastric vs Postgastric 4 Pregastric: Fermentation that occurs in the rumen of ruminant animals. It occurs before food passes into the portion of the digestive tract in which digestion actually occurs. 4 Postgastric: The fermentation of feed occurs in the cecum, behind the area where digestion has occurred.

Pregastric vs Postgastric 4 Ruminants –More efficient –Less intake 4 Non- ruminant herbivores –Only postgastric –Less efficient –Greater intake

Monogastric Systems 4 Mouth: prehension and chewing of food; some carbohydrate enzyme activity 4 Esophagus 4 Stomach –Storage –Muscular movements (break down food) –Secretes Digestive Juices (hydrochloric acid) pH about 2

Monogastric Systems

Small Intestine 4 Duodenum –Active Digestion Site –Produce enzymes Pancreas –Helps to neutralize ingesta entering the SI Liver –Produces bile; breaks down fats Intestinal Walls

Small Intestine 4 Jejunum –Active in nutrient absorption 4 Ileum –Active in nutrient absorption 4 Villi 4 pH 6 to 7

Large Intestine 4 3 Sections –cecum –colon –rectum 4 Active in water resorption 4 Secretion of some minerals 4 *Bacterial Fermentation*

Horses are Different 4 Saliva –contains no enzymes –may secrete up to 10 gallons/day –stimulated by scratching 4 Esophagus –only one way peristaltic movement Impossible for regurgitation

Horses are Different 4 Stomach –much smaller in comparison to other species –not very extensive muscular contraction –So how should we feed differently? 4 Small Intestine –same as pig but no gall bladder Can’t handle a high fat diet

Horses are Different 4 Large Intestine –over 60% of GIT –4 parts cecum large colon small colon rectum

Cecum and Large Colon 4 Similar to Rumen –bacterial cellulose breakdown –bacterial protein breakdown –VFA production –Water Soluble Vitamin production

Small Colon and Rectum 4 Primary site for water resorption 4 Can become impacted with feed

Horse GI Tract

Avian Species 4 Beak –no teeth –can be used to reduce particle size 4 Esophagus –ingesta holding and moistening –Salivary Amylase –Fermentation in some species

Avian Species 4 Proventriculus –Gastric juice production –pH 4 –Rapid pass through of food

Avian Species 4 Gizzard (ventriculus) –thick muscular wall –particle size reduction (similar to mastication) –nonglandular –normally contains grit –no enzymatic secretion

Avian Small Intestine 4 Functions in digestion and absorption of feed and nutrients just as in other monogastrics 4 pH is slightly acidic 4 Most enzymes found in mammals except?

Avian Large Intestine 4 Contains 2 blind pouches instead of ? 4 Mostly water absorption 4 Some bacterial activity but less than in most mammals 4 very short in comparison

Avian Species

Ruminant Digestive System 4 Mouth –what is unique about the teeth? –Can only chew on one side of mouth at a time 4 Saliva production is continuous 4 Production about 12 gallons/d

Rumen Stomach 4 4 PARTS –reticulum –rumen –omasum –abomasum

Reticulum 4 Honeycomb 4 most cranial 4 not truly separated from rumen 4 no enzymatic secretion 4 walls are tough, tend to catch heavy objects

Rumen 4 Large compartment extends from diaphragm to pelvis 4 papillae 4 Fermentation chamber 4 Majority of absorption of byproducts and conversion to volatile fatty acids

Rumen Digestion 4 Reticulorumen provides a favorable environment for bacterial fermentation 4 Continuous turnover of digesta and removal of fermented digesta 4 Anaerobic fermentation

Omasum 4 Manyplies (Stockmans Bible) 4 short blunt papillae 4 very muscular 4 no enzymatic secretion 4 reduction of particle size 4 water resorption

Abomasum 4 True Stomach 4 First Glandular portion of the tract 4 Very similar in structure and function to nonruminant stomach

Other Unique Points 4 Esophageal Groove –cardia to omasum –milk bypass 4 Rumination: The process where rumen contents are regurgitated, remasticated, and reswallowed for further digestion 4 Eructation: expulsion of accumulated fermentation gases from rumen via esophagus

Ruminant GI Tract

Rumination 4 Regurgitation of ingesta with mastication –reticular contraction that concentrates ingesta at the cardia –increased inhalation of air at same time –contraction of diaphragm –ballooning of esophageal walls –ingesta sucked into esophagus –returned to mouth by reverse peristalsis

Rumination 4 Excess liquids are swallowed 4 Mastication commences 4 More time spent masticating here than initial intake 4 Amount of time ruminating is a function of diet composition

Rumen Contents and Motility 4 Rumen contents are not uniform 4 Occur in stratified layers 4 Change from ventral to dorsal 4 Rumen mat –high concentrate diets eliminate mat –more viscous fluid in high grain diets –lowest dry matter in high forage diets

Rumen Contents and Motility 4 Motility of rumen mixes contents 4 Divided into –primary contractions –secondary contractions 4 Contractions require up to 50 seconds to complete

Rumen Contents and Motility 4 Contractions begin with reticulum 4 Progress dorsally 4 Finish with ventral blind sac and ventral pillars

Rumen and Acute Acidosis 4 Optimal rumen pH is Variation in pH is normally +/ Introduction of high grains result in –breakdown of rumen mat –proliferation of facultative anaerobes –these produce high levels of lactic acid

Rumen and Acute Acidosis 4 Lactate is a much stronger acid that other VFAs 4 In severe cases lactate can make-up well over 50% of total rumen acids 4 Succinate and Formate can also appear in high quantities

Rumen and Acute Acidosis 4 Increased acids can reduce pH as far as Severe rumenitis occurs at these pH levels 4 Absorption of lactic acid results in systemic acidosis 4 All chronic acidosis results in rumen parakeratosis

Factors Affecting Digestibility 4 Rate of passage: increased rate of passage of digesta through the tract reduces digestibility –Factors increasing rate of passage include: Increased level of feeding/intake (ruminants) Finer processing (such as grinding) of feed Note: grinding grain usually increases digestibility but grinding hay decreases digestibility