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 Reduces particle size
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
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 Eructation
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 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. Esterified Plant Lipid
Lipolysis
+ 3H20 +
Lipases
Esterified Plant Lipid
Free Fatty Acids

30. Weight percent of fatty acids
Biohydrogenation
Weight percent of fatty acids
Fatty acid
Diet
Abomasal digesta
16:0 (palmitic)
18:0 (stearic)
18:2 (linoleic)
18:3 (linolenic) 26 6 17 31 29 45 4
Sheep fed alfalfa hay

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

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

33. Biohydrogenation of 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
Species
Type pH
Ruminococcus flavefaciens
Fibrobacter succinogenes
Megasphaera elsdenii
Streptococcus bovis
fiber
lactate user
lactate producer
6.15 6
4.9
4.55

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