Lecture 12 - Ruminant Microbiology Flashcards
What is the microbiota
Ecological community of commensal, symbiotic, and pathogenic microorganisms that share our body space
Most numerous microbe is
Bacteria, then archaea
How are mammals “superorganisms”
Metabolic capability is a product of our own genetic potential plus that of our inhabitants
There is competition, but also _____________ between bacteria
Cross-feeding
How can we classify bacteria
Traditionally
- morphology (size, shape, gram)
- energy source
- fermentation endproducts
Modern = molecular characterization
What is typically used as a phylogenetic marker in microbes? Why?
Ribosomal rRNA (16S rRNA)
Genetically stable, composition (conserved and variable regions)
Some environments that microbes may live in in the rumen
Particle associated, liquid phase, adherent to rumen wall, omasal laminae, or inside other organisms
Functions of microbes
Provide nutrients
Detoxify the diet
Most GI bacteria are…
Obligate anaerobes
Name the different fermentative capabilities/classes of bacteria (11)
Cellulolytic, xylanolytic, amylolytic, dextrinolytic, pectinolytic, proteolytic, lipolytic, methanogenic, amino acid degrading, glycerol utilizing, lactate utilizing
Growth requirements and end products of cellulolytic and hemicellulolytic bacteria
Needs: pH 6-7, NH3
End products: acetic and butyric acid, CO2, H2
Common amylolytic bacteria
Streptococcus bovis
When does step bovis grow vs not grow
Present in low numbers when on forage or after adaptation to grain diet
Bloom in response to rapid infusion of starch
Strep bovis ferments what to what, causing?
Starch to lactic acid = lactic acidosis
What is lactic acidosis
Lactic acid accumulation in the rumen
What causes lactic acidosis
Overfeeding or quick change to high concentrate diet
Bloom of amylolytic bacteria (S. bovis) which produce lactate (lower pH)
pH drop = acid tolerant bacteria take over (Lactobacillus)
In lactic acidosis, when pH drops and acid tolerant bacteria take over, what happens?
Draws water from circulation into rumen = dehydration
Lysis of gram-negative bacteria = inflammation of rumen wall
How do we cure an animal with lactic acidosis
Rumen transplant from a healthy animal
Ways to prevent acidosis
- introduce concentrate slowly, don’t overfeed (rumen microbes will adapt to concentrate)
- target culprits (S bovis) w antimicrobial
How does the rumen microbial population adapt to high concentrate diets
Other amylolytic bacteria will compete with S bovis if increased slowly and they will make something else (e.g. propionate)
Bacteria and protozoa capable of utilizing lactate will increase
Growth requirements, fermentation end products of amylolytic bacteria
Need: pH 5-6, CO2, NH3, peptides
Endproducts: acetic acid, propionic acid, butyric acid, CO2
Acid-utilizing bacteria use… Creating the fermentation end products…
Use lactic acid, succinic acid, formic acid
End products are acetate, propionate
What do lipolytic bacteria do
Hydrolyze triglycerides and phospholipids with lipases
What do proteolytic bacteria do
Protein as energy source
Two classes of archaea **
- Free living
- Associated with protozoa
Archaea associated with protozoa produce… What negative effects does this have
Produce methane
Energy waste, greenhouse gasses
Where are rumen fungi prevalent? Important for what
On grasses more than legumes
Important in fiber digestion
What is legume bloat
Rapid release of proteins results in rapid production of gas by bacteria leading to froth (alfalfa, red and white clover)
What is bloat? One cause is… How do we reduce gas production
Fluid/foam in cardia prevents eructation
Genetic effect
Use antifoaming agents or ionophores to reduce gas
What causes nitrite toxicity
Excess nitrates accumulate in plants when they are stressed (droughts, hot dry winds)
What do rumen bacteria normally do to nitrate
Reduce it to nitrite then ammonia
What does nitrite do
Nitrite binds to hemoglobin preventing it from carrying oxygen
How to prevent nitrite toxicity
Increase nitrates gradually, rumen bacteria will adapt and remove it
Where is mimosine found? What does it do? Get rid of it by…
In tropical legume
Causes goiters/toxicity in ruminants
Degraded by bacteria Syngergistes jonesii
Two families of rumen protozoae
- Isotrichidae (Holotrichs: cilia over entire body
- Oligotrichs: cilia in mouth region
Characteristics of protozoa (5)*
Larger than bacteria
Slower to replicate than bacteria
Do not readily pass in rumen
Store soluble CHO
Engulf and lyse bacteria
Holotrichs exhibit…
Chemotaxis, move to back of rumen when animals are eating, settle in ventral/cranial sacs
Why do protozoa store CHO as amylopectin-like storage polysaccharides
Maintains constant energy source, stabilizes fermentation (prevents acidosis) in ruminant
Fermentation end products of holotrichs vs oligotrichs
Holo: acetate, propionate, lactate, H2
Oligo: CO2, H2, acetate, butyrate
N requirements of protozoa
Do not use NH3 (non-protein nitrogen)
Actively proteolytic
Advantages and disadvantages of protozoa
Adv: cellulose digestion, slower fermentation of starch, greater VFA production
Dis: reduced efficiency of protein use and increased rumen NH3 due to rumen protein turnover. CH4 production
Effects of defaunation
Increased daily gain, feed efficiency, microbial protein flow to duodenum, production of propionate
Decreased cellulose digestion, pH on high concentrate diets, production of butyrate
What is defaunation
Killing protozoa
How do high forage vs high concentrate diets affect rumen microbe population
High forage = high pH, increase cellulolytic bacteria, methanogens and protozoa
High concentrate = low pH, increase amylolytic bacteria, reduce methanogens and protozoa
Results of feeding ionophores
Increased propionate
Reduced protein degradation, deamination, methane production, lactate production
