Digestion in ruminants
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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.

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Ruminants l.jpg
Ruminants

  • 2.8 billion domesticated ruminants

  • ungulates

  • Pregastric fermentation

  • 4 compartment stomach

    • reticulum

    • rumen

    • omasum

    • abomasum


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Reticulum

  • Honeycomb lining

  • Formation of food bolus

  • Regurgitation initiated here

  • Collects hardware (nails, wire)


Rumen l.jpg
Rumen

  • Digestion and fermentation vat

  • Contains anaerobic microbes

  • Papillae lining

  • Absorption of VFA


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Omasum

  • Laminae/manyply lining

    • muscular folds

  • Reduces particle size

  • Absorption of water

  • Absorption of VFA


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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)



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Rumen Fermentation

  • World’s largest commercial fermentation

    • 100 billion liters in domestic animals

    • 1010 to 1012 cells/mL

    • 200 liters (50 gallons) in cows


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Ruminants

  • Continuous culture fermenters

    • input and output

  • Lignocellulosic substrates used

  • 8 x 1015 mouths to feed


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Rumen Environment

  • pH 6.0 – 7.0

  • Highly reduced

  • 10 – 15% dry matter

  • 39°C

  • 260 – 280 mOsm


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Rumen Microbes

  • Bacteria

    • >200 species with many subspecies

      • 25 species at concentrations >107/mL

    • 1010 to 1012 cells/mL

    • 99.5% obligate anaerobes


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Rumen Microbes

  • Protozoa

    • Large (20-200 microns) unicellular organisms

    • Prey on bacteria

    • Numbers affected by diet


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Rumen Microbes

  • Fungi

    • Known only for about 20 years

    • Numbers usually low

    • Digest recalcitrant fiber


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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


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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


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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


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Microbes to Ruminants

  • Provision of B vitamins

    • Meets the ruminant’s requirements under most conditions

      • Niacin may be beneficial in early lactation dairy cows


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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


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Symbiotic Relationship

  • Ruminants provide to microbes

    • Housing

    • Garbage removal

    • Nutrients

    • Neutral environment


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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


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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


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Ruminants to Microbes

  • Nutrients

    • Animal eats

    • Saliva provides urea (N source for bacteria)


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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


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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


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Rumination

  • 10 – 12 hours/day

  • Reduces particle size

    • only small particles leave reticulorumen

  • Increases surface area for microbial fermentation

  • Breaks down impervious plant coatings


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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


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Bacterial Digestion of Lipid

  • Microbial lipases act on triglycerides

  • Biohydrogenation

    • Addition of H across double bond to saturate unsaturated fatty acids


Lipolysis l.jpg
Lipolysis

+ 3H20

+

Lipases

Esterified Plant Lipid

Free Fatty Acids


Biohydrogenation l.jpg
Biohydrogenation

Sheep fed alfalfa hay


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Biohydrogenation

  • Reduction of double bonds

  • Result: fatty acids that are more saturated with hydrogen

Unsaturated

Saturated


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Biohydrogenation

18:2 converted (%)

Time (h)

  • (adapted from Harfoot et al., 1973)


Biohydrogenation of linoleic acid l.jpg
Biohydrogenation of Linoleic Acid

Linoleic acid

cis-9, trans-11 CLA

trans-11 18:1

18:0

isomerase

reductase

reductase


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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


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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



Factors that maximize microbial growth l.jpg
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


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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


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