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

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 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

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

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

Lipolysis

+ 3H+ 3H2200

++

Esterified Plant Lipid

Lipases

Free 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)

2661731

294546

Sheep fed alfalfa hay

Biohydrogenation Reduction of double bonds Result: fatty acids that are more

saturated with hydrogen

Saturated

Unsaturated

0

20

40

60

80

100

0 1 2 3 4 5 6

18:2 con. 18:2 t11 18:1 18:0

Biohydrogenation

Time (h)

18:2

co

nve

rted

(%

)

(adapted from Harfoot et al., 1973)

Biohydrogenation of Linoleic Acid

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 flavefaciensFibrobacter succinogenesMegasphaera elsdeniiStreptococcus bovis

fiberfiber

lactate userlactate

producer

6.156

4.94.55

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