Digestion in Ruminants

1. Digestion in Ruminants

2. Ruminants • 2.8 billion domesticated ruminants • ungulates • Pregastric fermentation • 4 compartment stomach • reticulum • rumen • omasum • abomasum

4. Reticulum • Honeycomb lining • Formation of food bolus • Regurgitation initiated here • Collects hardware (nails, wire)

5. Rumen • Digestion and fermentation vat • Contains anaerobic microbes • Papillae lining • Absorption of VFA

6. Omasum • Laminae/manyply lining • muscular folds • Reduces particle size • Absorption of water • Absorption of VFA

7. Abomasum • True gastric stomach • Proteolytic enzymes • Gastric digestion • Decreased pH from 6 to 2.5 • Denatures proteins • Kills bacteria and pathogens • Dissolves minerals (e.g., Ca3(PO4)2)

8. Omasum and Abomasum

9. Rumen Fermentation • World’s largest commercial fermentation • 100 billion liters in domestic animals • 1010 to 1012 cells/mL • 200 liters (50 gallons) in cows

10. Ruminants • Continuous culture fermenters • input and output • Lignocellulosic substrates used • 8 x 1015 mouths to feed

11. Rumen Environment • pH 6.0 – 7.0 • Highly reduced • 10 – 15% dry matter • 39°C • 260 – 280 mOsm

12. Rumen Microbes • Bacteria • >200 species with many subspecies • 25 species at concentrations >107/mL • 1010 to 1012 cells/mL • 99.5% obligate anaerobes

13. Rumen Microbes • Protozoa • Large (20-200 microns) unicellular organisms • Prey on bacteria • Numbers affected by diet

14. Rumen Microbes • Fungi • Known only for about 20 years • Numbers usually low • Digest recalcitrant fiber

15. Symbiotic Relationship • Microbes provide to the ruminant • Digestion of cellulose and hemicellulose • Provision of high quality protein • Provision of B vitamins • Detoxification of toxic compounds

16. Microbes to Ruminants • Digestion of cellulose and hemicellulose • Cellulases are all of microbial origin • Without microbes, ruminants would not be able to use forage crops such as pasture, hay or silage

17. Microbes to Ruminants • Provision of high quality protein • 50-80% of absorbed N is from microbes • Improved microbial efficiency will provide more microbial protein • Can get over 3 kg of microbial protein per day • High biological value protein source • Amino acid pattern is very similar to that required by the ruminant animal

18. Microbes to Ruminants • Provision of B vitamins • Meets the ruminant’s requirements under most conditions • Niacin may be beneficial in early lactation dairy cows

19. Microbes to Ruminants • Detoxification of toxic compounds • Example • Mimosine in Leucaena causes problems • poor growth, reproduction and hair loss • Hawaiian ruminants, but not those from Australia, have microbes that degrade mimosine so Leucaena could be fed • Transferred rumen fluid to Australia • Inoculated rumen • Fed Leucaena

20. Symbiotic Relationship • Ruminants provide to microbes • Housing • Garbage removal • Nutrients • Neutral environment

21. Ruminants to Microbes • Housing • Reliable heat • 39 ± 2°C • Guaranteed for 18 to 96 hours depending on diet and type of animal • Straw-fed water buffalo – longest rumen residence time • Small selective browsers (mouse deer or duiker) – shortest time

22. Ruminants to Microbes • Garbage removal • Absorption of VFA • Energy to ruminant • Eructation • CO2 and CH4 • Passage of indigestible residue and microbes to lower GI tract

23. Ruminants to Microbes • Nutrients • Animal eats • Saliva provides urea (N source for bacteria)

24. Ruminants to Microbes • Neutral environment • pH 6.5 to 7.0 • Saliva contains bicarbonate and phosphate buffers • Cows produce up to 46 gallons of saliva daily • Added during eating and rumination • Cow ruminates 10-12 hours/day

25. Ruminants to Microbes • Neutral environment • If pH 5.7 rather than 6.5 • 50% less microbial synthesis • Rate of carbohydrate use is decreased • More lactate and less acetate is produced • Further downward pH spiral • In concentrate selectors (like deer), parotid salivary glands are 0.3% of body weight

26. Rumination • 10 – 12 hours/day • Reduces particle size • only small particles leave reticulorumen • Increases surface area for microbial fermentation • Breaks down impervious plant coatings

27. Bacterial Digestion of Protein • Microbes utilize N, amino acids and peptides for their protein synthesis • Microbes convert dietary proteins into their own proteins • some amino acid conversion occurs so dietary amino acids does not equal amino acids leaving the rumen

28. Bacterial Digestion of Lipid • Microbial lipases act on triglycerides • Biohydrogenation • Addition of H across double bond to saturate unsaturated fatty acids

29. Lipolysis + 3H20 + Lipases Esterified Plant Lipid Free Fatty Acids

30. Biohydrogenation Sheep fed alfalfa hay

31. Biohydrogenation • Reduction of double bonds • Result: fatty acids that are more saturated with hydrogen Unsaturated Saturated

32. Biohydrogenation 18:2 converted (%) Time (h) • (adapted from Harfoot et al., 1973)

33. Biohydrogenation of Linoleic Acid Linoleic acid cis-9, trans-11 CLA trans-11 18:1 18:0 isomerase reductase reductase

34. Factors that Reduce Microbial Growth • Rapid, dramatic ration changes • Takes 3-4 weeks for microbes to stabilize • Feed restricted amounts of diet • Feed lots of unsaturated fat • Bacteria do not use fat for energy • Inhibit fiber digestion and microbial growth • Different types of fat have different effects

35. Factors that Reduce Microbial Growth • Feed lots of non-structural carbohydrate to lower rumen pH (rumen acidosis) • Slug feeding • Feed barley or wheat • To prevent acidosis, must balance lactate users and producers

36. Bacteria and pH Tolerance

37. Factors that Maximize Microbial Growth • Maximum dry matter intake • Balanced carbohydrate and protein fractions • Bacteria need both energy and N for amino acid synthesis • Gradual ration changes • Maintain rumen pH • Keep feed available at all times

38. Why Worry about Rumen Microbes? • Microbes make ruminants less efficient • Aerobic fermentation • Anaerobic fermentation Glucose + O2 ATP + CO2 + H2O Glucose acetic acid + propionic acid + butyric acid + CO2 + H2O + CH4 + Heat