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Anatomy of the Ruminant Digestive Tract

Anatomy of the Ruminant Digestive Tract. Taxonomy of Ruminants. Subclass – Ungulata Order – Artiodactyla Suborders Ruminantia Families Tragulidae Chevrotain, mouse deer Giraffidae Giraffes Cervidae Deer, moose Bovidae Largest family (120 species)

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Anatomy of the Ruminant Digestive Tract

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  1. Anatomy of the Ruminant Digestive Tract

  2. Taxonomy of Ruminants • Subclass – Ungulata • Order – Artiodactyla • Suborders • Ruminantia • Families • Tragulidae • Chevrotain, mouse deer • Giraffidae • Giraffes • Cervidae • Deer, moose • Bovidae • Largest family (120 species) • Pronghorn, african antelope, bison, buffalo, cattle, goats, sheep • Tylopoda • Family • Camelidae • Camels, Llamas

  3. Domesticated ruminant species • 3.5 billion animals • 95% are cattle, sheep, or goats • Major domesticated ruminant species • Cattle • Sheep • Goats • Buffalo • Reindeer • Yak • 75 million wild ruminants

  4. Classification of ruminants by feeding preference • Classes of ruminants • Concentrate selectors • Intermediate feeders • Roughage grazers

  5. Concentrate selecting species • Properties • Evolved early • Small rumens • Poorly developed omasums • Large livers • Limited ability to digest fiber • Classes • Fruit and forage selectors • Very selective feeders • Duikers, sunis • Tree and shrub browsers • Eat highly lignified plant tissues to extract cell solubles • Deer, giraffes, kudus

  6. Chevrotain Common Duiker Suni Kudu

  7. Intermediate feeding species • Properties • Seasonally adaptive • Feeding preference • Prefer browsing • Moose, goats, elands • Prefer grazing • Sheep, impalas

  8. Roughage grazing species • Properties • Late evolved • Generally larger rumens • Slows retention times • Less selective • Digests fermentable cell wall carbohydrates • Classes • Fresh grass grazers • Buffalo, cattle, gnus • Roughage grazers • Hartebeests, topis • Dry region grazers • Camels, antelope, oryxes

  9. Advantages of pregastric fermentation • Make better use of alternative nutrients • Cellulose • Nonprotein nitrogen • Ability to detoxify some poisonous compounds • Oxalates, cyanide, alkaloids • More effective use of fermentation end-products including: • Volatile fatty acids, microbial protein, B vitamins • Decrease in handling undigested residues • In wild animals, it allows animals to eat and run

  10. Disadvantages of pregastric fermentation • Fermentation is inefficient • Energy • Loss Amount (% of total caloric value) Methane 5-8 Heat of fermentation 5-6 • Relative efficiency is dependent on the diet NDF. • Protein • Protein • Some ammonia resulting from microbial degradation will be absorbed and excreted • 20% of the nitrogen in microbes is in the form of nucleic acids • Ruminants are susceptible to ketosis • Ruminants are susceptible to toxins produced by rumen microbes • Nitrates Nitrites • Urea Ammonia • Nonstructural carbohydrates Lactic acid • Tryptophan 3-methyl indole • Isoflavonoid estrogens estrogen Coumestans

  11. The ruminant digestive tract • Lips • Range from short, relatively immobile in nonselective grazing species to very mobile (prehensile) in selective grazing or concentrate selecting species

  12. Ruminant teeth • Dental formula for cattle and sheep Jaw Upper Lower Incisor 0 4 Canine 0 0 Premolar 3 3 Molar 3 3 • Outstanding characteristic • Upper jaw is wider than lower jaw • Ruminants animals chew in a lateral(grinding) motion on one side of mouth at a time • Needed to increase surface area of feed particles • Chewing primarily done during rumination in grazing species • Results in premolar and molar teeth becoming concave and beveled • Upper jaw fits lower jaw.

  13. Tongue • Structure • Muscle covered with a mucus membrane • Shape varies from being short and piston-like to long and slender • Uses • Aid in chewing and forming boluses • Aid in drinking • Prehension of feed • Covered with rough, hook-like papillae that assist in grasping feed • Important in nonselective grazing species • Taste • Taste buds located on: • Fungiform papillae distributed across tongue • Vallate papillae found on the back of the tongue • More numerous than monogastric species • More numerous on nonselective grazing species

  14. Taste in ruminants Calves Sucrose, xylose Select Fructose, glucose Select Lactose, maltose Indifferent Saccharin Indifferent Acid Intolerant Alkali Tolerant Salt Tolerant Mature cattle Sweet Strong preference Sour Mild preference Salt Preference (?) Bitter (alkaloids) Strong rejection • Believed that taste is primarily used for food avoidance by grazing species while concentrate selecting species select on the basis of smell.

  15. Pharynx • Structure similar to monogastrics • Involved in rumination and eructation

  16. Esophagus • Involved in rumination • Differences from monogastric esophagus • Circular and longitudinal muscles are striated muscle along the entire length • Provides greater strength • Allows some voluntary control • Funnel shaped • Positioned between lungs • Mucous membrane is comprised of stratified squamous epithelial tissue • Contains 3 sphincters • Pharyngo-esophageal • Diaphragmatic • Cardiac • Slit-like • 1” long • Sphincters active in rumination and eructation

  17. Regions of the ruminant stomach % of mature ___Volume, l___ __volume__CattleSheep Rumen 80 60-100 9-18 Reticulum 5 Omasum 5-8 6-10 1-2 Abomasum 5-8 5-8 2 • Full capacity of the reticulorumen is only used in animals fed low quality roughages. Only 60 to 70% of the total capacity is used in animals fed high quality roughages.

  18. The ruminant stomach

  19. Structures within the reticulorumen • Folds • Areas of tissue dividing the reticulum and rumen into different compartments • Functions • Mixing and particle sorting • Prevent fluid from reaching the cardia during eructation • Pillars • Highly muscled areas of the rumen that form grooves on the outside of the rumen • Contains blood vessels, lymph, and nerves • Functions • Contractions

  20. Structures within the reticulorumen • Papillae • Finger-like structures (10mm x 2 mm) covering the rumen wall • Particularly well-developed in ventral portion of the rumen • Few present on pillars in roughage-selecting species, but more evenly distributed across rumen in concentrate-selecting species • Function • Increase absorptive surface for VFAs.

  21. Structure of the rumen wall • Non-secretory stratified epithelium covers was of reticulum, rumen, and omasum • Layers • Stratum basale • Columnar epithelium with .5 um between cells • Hemidesmosomes connect to basement membrane • Nuclei • Numerous mitochondria • Stratum spinosum • Oval-shaped • Desmosomes connect cells with tonofibrils for nutrient transport • Nuclei • Fewer mitochondria • Stratum granulosum • Flat cells • Connected by tight junctions • Nuclei and mitochondria degenerate • Stratum corneum • No nuclei or mitochondria • Tough layer of horny mucopolysaccharide • .1 um between cells • Sloughs into digesta

  22. Parakeratosis (Incomplete keratinization of the rumen wall) • Occurs in ruminants fed high grain diets for relatively long periods • Symptoms • Thickening of the horny layer (Hyperkeratosis) • Incomplete keratinization • Absence of the stratum granulosum • Retained nuclei in keratinized cells • Particularly bad on papillae • Papillae shorten and thicken • Increased number of branched papillae • Debris collects in interpapillary spaces causing lesions • Bacteria (Sphaeromonas necrophorus and Cornybacterium pyrogenes) enter blood stream and form liver abscesses • Cause • High concentrations on VFAs, particularly butyrate

  23. Low concentrations Metabolized to ketones in the epithelium causing anoxia Stimulates blood flow May be a detoxifying mechanism against n-butyrate Increases insulin and IGF-1 concentrations Stimulate cell proliferation Increases normal epithelial growth High concentrations Levels overcome capacity for metabolism to ketones N-butyrate inhibits DNA synthesis Mitosis inhibited Increases insulin and IGF-1 concentrations Stimulate cell proliferation Incomplete maturation of epithelium Effects of butyrate concentration on structure of rumen epithelium

  24. Blood circulation to and from the ruminant stomach • Supply • Abdominal aorta • Celiac-mesenteric trunk • Arteries • Common hepatic • Right ruminal • Left ruminal • Left gastric • Drainage • Veins • Reticular • Right ruminal • Left ruminal • Omasal-abomasal • Portal vein • Liver

  25. Factors increasing blood flow to the rumen • Carbon dioxide in epithelium • Volatile fatty acids • Feeding • Sight or smell of feed (slight)

  26. Innervation of the rumen stomach • Vagus nerve • Involved in both sensory and motor pathways • Controls contractions of reticulum and rumen, rumination, and reflex of the reticular groove • Sphlanchic nerve • Minor role in contractions • Intrinsic nerve • A rich ganglionic plexus is present in the subepithelial region of all compartments of the stomach ranging in cells 18 to 40 um in diameter • Small cells innervate reticular groove, reticulum and pillars of the rumen • Larger cells innervate abomasum • Functions • Vasodilatory • Some control on muscle contractions

  27. Tension receptors Most common Found in muscle layers in reticulum, reticuloruminal fold, cranial sac, and lips of reticular groove Excited by low thresholds of distension or contractions Slow acting response Action Increase contractions and salivation Epithelial receptors Found near basement membrane in reticulum, cranial sac, and longitudinal pillars Stimuli High threshold distension Liquid movement Volatile fatty acids Rapid acting (mechanoreceptors) or Slow acting (chemoreceptors) Action Inhibit contractions Sensory receptors of the reticulorumen • Simple nerve endings • All afferent vagal fibers • Few receptors in the sacs of the rumen

  28. Omasum • Lies to right of rumen • Entrance is the reticulo-omasal orifice • 1 inch slit in cattle • Lined with small papillae • Controls particle of digesta leaving reticulorumen • Round organ containing 100-150 flat parallel sheets (laminae) covered with conical papilae • Because of sheets, omasum has 1/3 of the surface area of the stomach in cattle and 10% of the stomach surface area in sheep • Sulcus omasi • Direct route for digesta from the reticulo-omasal orifice and omaso-abomasal opening • Fills by reticular contractions and aspiration

  29. Functions of omasum • Filter large particles Diameter of particles, mm >5 3-5 2-3 1-2 <1 % Rumen 2.5 9.6 20.1 35.1 32.7 Reticulum 2.4 8.5 17.9 34.0 37.3 Omasum .1 .8 5.9 25.4 68.0 Abomasum .7 2.5 7.4 24.6 64.7 • VFA absorption • 43 to 77% of VFAs entering or 10% of total produced • 85% of VFAs produced are absorbed before abomasum • Exchanged for Cl- • Improves efficiency of absorption • Prevents buffering of the abomasum • VFAs are strong buffers with a pK of 4.6 • Abomasum functions at pH 2 • Water absorption • 30 to 60% of water entering • Magnesium absorption

  30. Regions of the abomasum Cardiac Epithelial Fundic Pyloric

  31. Lining of the different regions of the abomasum • Fundic region • Contains gastric glands lined with secretory columnar epithelium • Chief cells • Secrete pepsinogen • Continuous • Parietal cells • Secrete hydrochloric acid • Variable • Pyloric region • Stratified squamous epithelium • Secrete mucus

  32. Surface of the abomasum • Arranged in 10 to 17 folds • Functions • Increase surface area • Increase approximately 7 times • Allows greater acid and pepsin secretion • Prevents stratification of feeds • Allows for mixing of digesta and enzymes • Regulate flow

  33. Secretion of the fundic region • Composition • pH 1.05 to 1.32 • Ionic (mEq/l) H+ Variable, up to 124 Na+ Variable, 21 to 167 Cl- 138 to 172 • Enzymes • Pepsinogen • Converted to pepsin by HCl • Lysozyme • Lyses bacteria • Secretion • 30 to 35 l/day in cattle • Amount of HCL secreted to keep pH < 3 • Pepsinogen secretion is constant • Factors that increase fundic secretion • Presence of digesta • Factors that stimulate rumen motility stimulate gastric secretion • Peak secretion of occurs 45 to 90 minutes after feeding • Presence of volatile fatty acids or lactic acid • Acts through the hormone, gastrin, secreted by the fundic and pyloric mucosa • Inhibition of secretion • Abomasal pH < 2 • Distension or presence of HCL in duodenum • Acts through the hormone, secretin

  34. Motility and digesta flow in the abomasum • Filled by contractions of the reticulorumen • Empties by contractions confined to the pyloric region • Flow from the abomasum • Greatest prior to and during feeding • Lowest flow occurs immediately after feeding • Ingesta remains in abomasum for 1 to 2 hours • As much as 10% backflows into abomasum • Factors affecting abomasal motility • Isotonic HCO3- in duodenum increases flow, while hypertonic HCO3- in duodenum decreases flow • Duodenal distension decreases flow • Long chain fatty acids inhibit abomasal motility • Acts through duodenal hormone, cholecystokinin • Lactic acid in duodenum inhibits ruminal motility and, therefore, abomasal filling • Acts through duodenal hormone, secretin • Increased dietary fiber decrease abomasal flow • Hyperglycemia decreases abomasal flow • May contribute to left abomasal displacement

  35. Regions of the small intestine Length, ft CattleSheepDigesta pHFunctions Total 90-150 60-110 Duodenum 3-4 2-3 2.7-4 Enzymes pH change Flow reg. Jejunum 60-100 - 4-7 Enzymes Absorption Ileum 30-50 - 7-8 Absorption Variable Fermentation • Rate of pH increase slower than monogastrics • Better for peptic activity • May limit pancreatic protease and amylolytic activity

  36. Pancreatic secretion • Secreted with bile in the common bile duct of sheep • 1 ft from pylorus • Secreted in the pancreatic duct of cattle • 3 ft from pylorus • Amounts secreted • 2.2 – 4.8 l/day (Cattle) • .3 to .4 l/day (Sheep) • Composition pH 7.2-7.8 Ionic (mEq/l) Na+ 135-165 K+ 4-5 Cl- 110-126 HCO3- 15-30 • Enzymes • Amylase • Lipase • Proteases • Trypsinogen converted to Trypsin • Chymotrypsinogen converted to Chymotrypsin • Procarboxypeptidase converted to Carboxypeptidase • Nucleases

  37. Activity of pancreatic enzymes • Concentration of enzymes in pancreatic juice comparable to monogastrics • Activity may be limited by: • Less juice secreted/kg BW • Low digesta pH • High rate of passage • Limited activity particularly a problem for intestinal digestion of starch escaping ruminal digestion. • On high grain diets, intestinal starch digestion may be as low as 48% (1kg).

  38. Factors affecting pancreatic secretion • H+ in duodenal digesta (HCL or Lactic acid) • Increases volume and HCO3- concentration • No effect on enzyme secretion • Acts through duodenal hormone, secretin • Fat in duodenal digesta • Slight increase in volume • Large increase in enzyme activity • No effect on HCO3- concentration • Acts through duodenal hormone, cholecystokinin

  39. Bile • Secreted with pancreatic juice in the common bile duct of sheep • Secreted in the bile duct of cattle about 2 ft from pylorus • Amount • 500-1500 ml/day in sheep • Composition • Ionic mEq/l Na+ 154 K+ 7 Cl- 122 HCO3- 23 • Lipid • Bile salts (Sodium taurocholate) • Phospholipids (Phosphotidylcholine) • Factors increasing secretion • Bile salts in the duodenum • HCl in the duodenum • Through secretin • Fat in the duodentum • Through cholecystokinin

  40. Small intestinal secretions • Duodenum • Secretion from the Brunner’s glands • pH 6.7 • Contains small amounts of amylase and ribonuclease • Jejunum and Ileum • Composition • Ionic (mEq/l) Upper jejunumLower Ileum Na+ 136 135 K+ 8 9 Cl- 134 105 HCO3- 12 42 • pH 7.1 8 • Enzymes • Enzymes • Lactase (in young) • Maltase • Isomaltase • Dipeptidases • Highest activity in upper to mid-jejunum • Activity may be breed-related.

  41. Digesta flow in the small intestine • Controlled by: • Duodenal hormones • Enteric nervous system in sub-mucosal and muscle layers • Flow by peristaltic contractions • Go both directions • May result in more rapid passage of large particles than small particles and liquids

  42. Large intestine structure • Size Rumen volume:LI volume Roughage selectors 15-30:1 Concentrate selectors 6-10:1 • Structure • Cecum • Blind sac • 25-25 cm long x 5-7 cm diameter (Sheep) • Colon and Rectum • Large tube with longitudinal folds • No villi

  43. Large intestine functions • Fermentative digestion • Bacteria similar to rumen, but no protozoa • LI digestion may account for as much as: • 27% of cellulose digestion • 40% of hemicellulose digestion • 10% of starch digestion • Only important in conditions that increase the amount of fermentative carbohydrate entering the LI • Increased rate of passage of forages • High grain diets • May account for as much as 17% of total VFA absorption • VFAs are efficiently absorbed, but primarily used as energy source for mucosa cells

  44. Large intestine functions (Cont.) • Absorption of ammonia-N • May account for as much as 30 to 40% of the net transport of N into body fluid • Absorbed N may be used for: • Synthesis of nonessential amino acids • Recycling of N to the rumen • Important on low protein diets • Regulated by: • Increased by increasing N concentration of diet • Decreased by increasing the amount of carbohydrate fermented in the large intestine. • Mineral absorption • Na, K, Ca, P, Co, Mn, Mg, Cu, Zn, Cl • Water absorption • 90% of water entering the LI

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