L28: Forestomach digestion Flashcards
animals that mainly eat grass are ?
grazers
animals that selectively feed on highly digestible material
browsers
can live off grass but aren’t ass efficient as grazers
why might browsers have larger parotid glands than grazers
parotid gland produces proline-rich proteins that bind and neutralize tannin
browser diets have much more tannin than grazers
what is the main difference in the rumen between browsers & grazers
unlike grazers, browsers have no fiber mat or stratification (not layered)
have homogenous rumen content
is this describing a browser or grazer rumen…
high viscosity fluid, separation due to flotation/sedminetation less possible, gas bubbles evenly distributed
browser
is this describing a browser or grazer rumen…
low viscosity fluid, separation due to flotation/sedementation & clear separation of gaseous layer
grazer
rumen papilla growth is stimulated by _______, so [ _______ ] is highest where microbial activity is highest
VFAs
VFA
rumen _____ reflects stratification & location of greatest microbial activity and absorption of VFA
papillation
the time that liquid or a food particle spends in the rumen
mean retention time (MRT)
in general, is rumen MRT longer for water or food particles
food
what is a benefit and disadvantage of a long MRT of food in the rumen
(+) improves utilization of cell wall constituents (fiber)
(-) restricts feed intake b/c intake is limited mostly by the capacity of the forestomach
who has an overall shorter MRT, browsers or grazers
browsers
why is food particle throughput smaller in browsers than grazers
they rely more on plant cell content which is easily fermentable
what is the benefit of higher fluid throughput in grazers
- helps remove waste & make room for new material
- removes microbes
how does removing waste and microbes stimulate bacterial growth
by maintaining appropriate conditions in the rumen which increases microbial yield
this only works if substrate supply is sufficient & balanced N:C ratio
what is quorum sensing
bacteria, through small signal molecules called autoinducers, regulate bacterial population density
involves regulation of gene expression of autoinducers to fluctuations in cell-population density
autoinducers increase in [ ] as a function of cell density
what is the function of the omasum?
- absorb water, electrolytes, VFAs, HCO3
- transport ingesta to abomasum
the _____ of the omasum create a huge increase in SA
laminae
the large volume of water coming from a grazers rumen is reabsorbed by the ?
omasum; grazers have larger omasums than browsers since they have a higher fluid throughput
why does more water flow through a grazer’s forestomach?
helps remove waste and microbial protein and facilitates better fiber fermentation
what are the substrates for microbial production of VFAs
- cellulose (Beta linked glucose polymers, insoluble CHOs)
- starch, glycogen, sugar (hexoses, alpha linked glucose polymers, soluble CHOs)
what are the endproducts of VFA fermentation (VFA –> hexose –> ?)
- acetate
- proprionate
- butyrate
what is the pka of VFAs
4.8
at a pH of 6.8, most VFAs exist in what form?
dissociated form
uses the VFA/HCO3 exchanger for intracellular transport
at pHs closer to the pKa of VFAs, how are VFAs absorbed
via diffusion ( [ ] gradient)
acetate enters the Krebs cycle as ?
Acetyl-CoA
propionate enters the Krebs cycle as?
Succinyl-CoA –> gluconeogenesis
buturate gets converted into _______ and then enters the Krebs cycle as _______
Beta hydroxybuturate (ketone body) in the rumen epithelium
enters Krebs as Acetyl-CoA
the most important gluconeogenic substrate; major source of glucose
propionate
if VFAs accumulate in the rumen, they lower ?
pH; favors microbes producing lactic acid
A high amount of _______ generate large amounts of VFAs quickly
easily digestible CHOs (beets/apples/grain)
how does pH affect microbial growth rate
each bacterial species has a pH range w/in which growth is possible; pH optimums
explain Rumenoacidosis
- carbohydrate overload leads to increases VFAs and decreased pH
- lactate production increases, further decreasing pH
what are the symptoms of rumenoacidosis
unspecific but… variable appetite, decrease in milk production, D+, bloat, reduced rumen motility, increased HR and breathing rate, laminitis
glandular digestion of microbial protein in the cow begins in the ?
abomasum via abomasal enzymes such as lysozymes
it then continues in the duodenum w/ pancreatic enzymes
what do lysozymes do
catalyze the hydrolysis of bacterial cell walls
how does lysozyme production in ruminants compare to most mammals
- ruminants secrete large amounts of lysozymes in the lumen of the abomasum
- most mammals produce moderate-high levels of lysozyme in tears and saliva, WBCs and tissue macros
T/F: lysozymes are most active at low pH
true
a measure for estimating how well a particular protein source is used
biological value
what is the purpose of urea recycling?
ruminants recycle urea via saliva into the rumen for usage by bacteria that turn it into microbial protein
aquaporins & urea transporter B are involved in ______ in ruminants
urea recycling
what is the purpose of urea recycling in hindgut fermenters/nonruminants
it is a salvage mechanism that improves Nitrogen retention during times of protein deficit
what determines the amount of microbial protein that reaches the small intestine
the amount of dietary crude protein & metabolic demand
what determines the amount of plasma urea in a ruminant
the amount of microbial protein that reaches the SI & the presence of excess ammonia
where does ammonia get absorbed, where does it get detoxified
rumen
detox in liver via urea cycle
what causes an accumulation of ruminal ammonia
if the rate of ammonia production or ingestion of ammonia exceeds the microbe’s ability to utilize it to form amino acids
what is urea poisoning / ammonia toxicosis
liver gets overwhelmed by the amount of ammonia, results in elevated blood ammonia levels
accumulation of ruminal ammonia can cause alkaline indigestion if pH exceeds 7.5 –> ruminal contractions inhibited
what anatomical structure diverts the flow of milk into the abomaum of a fetus
esophageal groove
explain rumen drinkers
fast drinking (no-little suckling of milk) can cause spill over into the rumen if the esophageal groove is not fully formed
milk ending up in the rumen gets fermented to lactic acid, decreases the pH, causing inflammation of the lining
lining becomes irritated & thickened; damages ability to contract and absorb nutrients
results in: malnutrition, bloat, acidosis, depression, weakness
