Digestion in Ruminants

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

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

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

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

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)

Omasum and Abomasum

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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