fermentative digestion Flashcards
what is the most renewable source of energy
biomass
what complex in plants is irresistible for breakdown
ligno-cellulose complex
how is cellulose linked
B1-4 linkage - crystalline structure
what is loosely bound to cellulose
hemicellulose
is lignin a carbohydrate
no - but it has a phenyl-propane base
what has the ability to unlock covalent linkages (expose) carbs followed by hydrolysis - fermentation
microbes
what does colonization by microbes in the digestive tract do
essential to exploid the fermentative capacity of mictobes
why do microbes derive energy and nutrients during fermentation
to grow
symbiosis
mutual benefit between herbiborous host and microbes
what are the 6 suitable conditions for fermentatibe digestion
- reservoir to house microbes in the digestive tract
- anaerobic environment
- pH range slighly acid to neutral ((>5.3) 6-7)
- dietary factors
- passage rates
- utilization of by-products and absorption of end products
what is GI modification
a region of GI tract enlarged to store food and allow microbiota to colonize and facilitate fermentation
describe hindgut modification in rabbits
caecum is modified to carry microbes that help in fiber digestion
what kind of feed is required for rabbits
high quality fiber
why do rabbits practice coprophagy
- feces is nutritious and shed at night
- recycle nutrients - microbial protein
describe hindgut ferementation in horses
caecum and colon are modified to carry microbes that help in fiber digestion
where are grains, proteins, and fats digested in horses
SI
what are the major fiber sources that are fermented in the caecum-colon in horses
pasture/hay
horses at ____ can meet their needs from microbial fermentation
maintenance
rumen and hindgut bacteria are strict __
anaerobes
why is the redox potential negative
electrons are better at exchanging when the system is in a reduced state
what does fermentation produce
metabolic hydrogen
what state is the GI in when there is more fiber in the diet
more reduced state
what two things happen when oxygen is introduced in feed and water
- diffuse across rumen and hindgut wall
- used by facultative anaerobes
what is an optimal pH for microbial growth
6 to 7
what is pH regulated by
- absorption of VFA
- buffers (bicarbonate and phosphate in rumen)
what pH of equines and cows cause significant GI and metabolic problems
<6; <5.4
what is the role of saliva in fermentation
ruminants
- 100-150 L/day
- lubrication
- buffering - NaHCO3
- fluid for rumen fermentation
what is the role of saliva in fermentation
equine
- 35-40 L/day
- flow associated with chewing
what are the feed intake patterns of cows
- meal based eaters
- multiple meals per day total eating time 2-3 hours with 7-12 hrs ruminating
- process feed slowly
what are the feed intake patterns of equines
- trickle feeders
- 16-18 hrs a day eating to maintain a full stomach and constant flow through GI tract
- process feed more rapidly - higher passage rates than foregut fermenters
fiber digestibility is higher in ____ fermenters than ____fermenters
foregut; hindgut
where is starch and protein digested in cows and equines
rumen; small intestine
what determines how much of feed is digested
degradation/passage and site of digestion
what is the microbiome comprised of
microbes, their genomes, and interactions with host/environment
what are the 4 types of microbes
- bacteria
- fungi
- archaea
- protozoa
what is the predominant microbe in the rumen
bacteria
what is bacteria present as
a fiber adherent, planktonic and epimural
what does bacteria play a key role in
fiber, starch , oligo- and monosaccharides fermentation, protein and lipid digestion
how is bacteria nomenclature based on
substrate
protozoa are only ____ and what are the two groups
ciliates; holotrichs and oligotrichs
what is the role of rumen protozoa
- strong assco. with bacteria and archaea
- predate on bacteria/methanogens - bateria turnover
- participate in fiber, starch, oligo- and monosaccharide fermentation, protein and lipid digestion
what are rumen anaerobic fungi
- important in ruminants in developing areas
- free swiming flagellated zoospores attach to plant particles and relate to carb digestion
what is the role of rumen archaea
not involved in feed digestion but are hydrogen scavengers and naturally form methane
what are the three pathways that methane is formed
- hydrogenotrophic methanogens
- methylotrophic methanogens
- aceticlastic methanogens
what are the nutritional requirements of microbes
- CO2
- Energy - ATP released during fermentation
- Nitrogen
- minerals
what do passage rates of feed depend on
- quality of feed
- feed intake
- feed characteristics
- digestion rates
- host
what is carb fermentation composed of
- neutral detergent fiber (NDF)
- non fiber carbohydrats
what are slowly fermented carbs
cellulose and hemicellulose
what are rapid fermended carbs
starch and pectin
what do high forage rations have
higher NDF and therefore a controlled rate of fermentation
what is a prerequisite for digestion of NDF
colonization of microbes to feed particles
how much of cellulose digestion occurs in the rumen
90%
what are the two stages of fiber digestion
- microbial attachment (colonization)
- slow process
- specific and non-specific binding - hydrolysis - enzymatic
- endoenzymes
- exoenzymes
- multi-enzyme complexes
more fiber in the diet leads to …..
VFA
more acetate and butyrate
more starch/grain in the diet lead to
VFA
propionate
runaway fermentation can lead to accumulation of
lactate
more hydrogen in the diet leads to
more methane
what are the two ways energy is lost
energy efficiencies
CH4 (16%) and heat of fermentation (6%)
how are VFA absorbed
- rumen papillae
- development senensitive to grain in diet (butryate stimulates development)
- by diffusion
- removes large am. of acid each day
what is acetate important for
precursor for milk fat
what is propionate important for
determinant of milk volume
gluconeogenic
what is butryate important for
stimulates rumen development and papillae length
how are carbs digested in equines
- balance of forage and grain
- forages fermented in caecum and colon
- starch and protein in SI
- if too much grain - colic, diarrhea or laminitis
- VFA provite immediate energy
microbes need protein in what form
nitrogen for growth (true protein and NPN, recycled microbia protein, endogenous N)
microbes prefer to utilize N from ….
ammonia and all N sources are converted to ammonia
what is proteolysis
- rapidly convert N sources to ammonia
- most bacteria are proteolytic
- beneficial to microbes but not to host
what is microbial protein synthesis
- N source from ammonia forms the building block for microbial protein formation
- need fermentable carbs to supply ATP
- beneficial to microbes and host
where does microbial synthesis occur
types of fermenters
foregut and hindgut fermenters
is there a need for dierary supplementation of lipids
no, microbes synthesize their own fatty acids - present as complex lipids
microbes cannot tolerate more than ____ in dietary lipids
3%
lipolysis
complex lipids are hydrolyzed to free fatty acids and glycerol by lipolytic bacteria
what is glycerol is converted to
VFA
what is biohydrogenation
conversion of unsaturated FA to saturated FA resulting in the formation of several isomers - bioactive fats
cis-9, trans 11 CLA
most abundant FA in milk
trans-10, cis-12 CLA
interferes with milk fat synthesis
what do increasing lipid concentrations increase
bacteria that participate in normal BH
what are the predisposing factors of disruptions in fermentative digestion
- excessive fermentation of starch
- low pH in rumen or cecum
- production of amines
- production of endotoxins
- laminitis, rumen parakeratosus, liver abscesses, lung abcesses
- laminitis and colic
what is SARA
- well organized digestive disorder in high producing dairy cows resulting in economic losses to dairy herds
- abrupt chnages in diet, increasing grain, inadequate fiber, fine particle size
what happens to the ruminal pH in SARA
drops to <5.5 and lactic acid accumulates
describe colic in horses
- abdominal pain and is the consequence of all forms of GI disease or problems
- 10-11% of horses suffer
what are the dietary of factors of colic
high grain, low fiber, abrupt feed changes, moldy feeds
- factors known to cause disturbances in hindgut microb pop.
