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Anatomy of the Ruminant Stomach

Anatomy of the Ruminant Stomach. Extensive pre-gastric microbial fermentation 4 compartments. Cow rumen. Cow reticulum. The interior surface of the rumen. Reticular epithelium. The inside of the omasum. Lining or epethelia of the reticulo-rumen. cattle (left), sheep (right).

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Anatomy of the Ruminant Stomach

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  1. Anatomy of the Ruminant Stomach • Extensive pre-gastric microbial fermentation • 4 compartments

  2. Cow rumen

  3. Cow reticulum

  4. The interior surface of the rumen Reticular epithelium The inside of the omasum

  5. Lining or epethelia of the reticulo-rumen cattle (left), sheep (right)

  6. Papillae most dense in the ventral sac • where most absorption occurs

  7. Papillae development Fermentation/absorption driving factor

  8. Reticular groove (pinned in an open position) cardia reticulo-omasal orifice

  9. Reticular groove (in a closed position) esophagus reticular groove

  10. Omasum tightly packed with digesta (left) leaves or folds

  11. Cow omasum

  12. Function of the Omasum • acts as a filter to sort out liquid and particles for passage to the abomasum • selective retention of the coarse particles • absortive site for water, VFA, Na, K, etc • reduction of the net volume entering the abomasum

  13. Abomasum duodenum pylorus fundic fundic folds (unique)

  14. Cow abomasum

  15. Function of the Abomasum • digesta to abomasum continuous • thus, continuous secretion of gastric juice (pepsin. HCl) • stimulated by VFA and lactic acid • short retention time (< 3 h) • digesta entering: pH 6.0 • digesta leaving: pH 2-3

  16. Motility • Mixing of digesta • passage of digesta through the reticular-omasal orifice

  17. Rumen motility • Contraction/relaxation of reticulo-rumen • moves and mixes digesta • passage of digesta through the reticular-omasal orifice • initial contraction of the reticulum • 2nd powerful contraction of reticulum • wave of contractions passing over rumen • about 60 secs

  18. Contraction sequence of RR

  19. Movement of Digesta

  20. Rumination - “cud-chewing” - regurgitation of digesta - re-swallowing of liquid and fine particles - mastication/ensalivation of bolus (40 - 70 sec) - pause (2 - 6 sec)

  21. Eating and ruminating • increases saliva secretion • helps reduce particle size of feed • promotes passage of digesta from the RR which alleviates gut fill

  22. GAS GAS GAS Eructation • Rumen contraction forces gas to the back and then forward • Gas forced up esophagus to the trachea

  23. Esophageal Fistulae

  24. Rumination boluses (liquid) down up

  25. Rumination boluses (dry) up down

  26. Role of rumination • saliva secretion • 2-4 x higher than during resting • particle size reduction

  27. alfalfa hay alfalfa hay orchardgrass corn silage Chewing activity of dairy cows Eating Ruminating 10 8 6 h/d 4 2 0 10 15 20 25 30 35 40 10 15 20 25 30 35 40 NDF-f (% DMI)

  28. Rumination by feedlot cattle Medium fine 75 Coarse 86 Medium 81 Fine 69 8.1 13.6 Diets contained 10% silage (DM basis) 9.3 15.8 6.8 13.3 Ruminating, h/d Total chewing, h/d Diets contained 5% forage (DM basis) Ruminating, h/d 4.4 5.5 Total chewing, h/d 7.3 7.9 9.4 16.1 Silage Straw

  29. Salivation • lubrication of feed for swallowing • passage of feed through the GI tract • buffers (bicarbonate, phosphate) acids produced during digestion • enzymic activity • no amylase in ruminants • pregastric esterase or lipase (preruminant) • nutrients for microbes: mucin, P Mg, Cl • anti-frothing properties (bloat)

  30. Salivary glands Parotid saliva: ~ 50 % of total saliva

  31. Amount of Saliva • parotid cannulation • total collection of saliva • only one duct • re-entrant parotid cannulation • collection at the cardia using a bag • requires partial rumen emptying

  32. Sheep Do animals that eat more slowly produce more saliva ?

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