L28: Forestomach digestion

Question 1

animals that mainly eat grass are ?

Answer 1

grazers

Question 2

animals that selectively feed on highly digestible material

Answer 2

browsers
can live off grass but aren’t ass efficient as grazers

Question 3

why might browsers have larger parotid glands than grazers

Answer 3

parotid gland produces proline-rich proteins that bind and neutralize tannin

browser diets have much more tannin than grazers

Question 4

what is the main difference in the rumen between browsers & grazers

Answer 4

unlike grazers, browsers have no fiber mat or stratification (not layered)

have homogenous rumen content

Question 5

is this describing a browser or grazer rumen…

high viscosity fluid, separation due to flotation/sedminetation less possible, gas bubbles evenly distributed

Answer 5

browser

Question 6

is this describing a browser or grazer rumen…

low viscosity fluid, separation due to flotation/sedementation & clear separation of gaseous layer

Answer 6

grazer

Question 7

rumen papilla growth is stimulated by _______, so [ _______ ] is highest where microbial activity is highest

Answer 7

VFAs
VFA

Question 8

rumen _____ reflects stratification & location of greatest microbial activity and absorption of VFA

Answer 8

papillation

Question 9

the time that liquid or a food particle spends in the rumen

Answer 9

mean retention time (MRT)

Question 10

in general, is rumen MRT longer for water or food particles

Answer 10

food

Question 11

what is a benefit and disadvantage of a long MRT of food in the rumen

Answer 11

(+) improves utilization of cell wall constituents (fiber)
(-) restricts feed intake b/c intake is limited mostly by the capacity of the forestomach

Question 12

who has an overall shorter MRT, browsers or grazers

Answer 12

browsers

Question 13

why is food particle throughput smaller in browsers than grazers

Answer 13

they rely more on plant cell content which is easily fermentable

Question 14

what is the benefit of higher fluid throughput in grazers

Answer 14

• helps remove waste & make room for new material
• removes microbes

Question 15

how does removing waste and microbes stimulate bacterial growth

Answer 15

by maintaining appropriate conditions in the rumen which increases microbial yield

this only works if substrate supply is sufficient & balanced N:C ratio

Question 16

what is quorum sensing

Answer 16

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

Question 17

what is the function of the omasum?

Answer 17

• absorb water, electrolytes, VFAs, HCO3
• transport ingesta to abomasum

Question 18

the _____ of the omasum create a huge increase in SA

Answer 18

laminae

Question 19

the large volume of water coming from a grazers rumen is reabsorbed by the ?

Answer 19

omasum; grazers have larger omasums than browsers since they have a higher fluid throughput

Question 20

why does more water flow through a grazer’s forestomach?

Answer 20

helps remove waste and microbial protein and facilitates better fiber fermentation

Question 21

what are the substrates for microbial production of VFAs

Answer 21

• cellulose (Beta linked glucose polymers, insoluble CHOs)
• starch, glycogen, sugar (hexoses, alpha linked glucose polymers, soluble CHOs)

Question 22

what are the endproducts of VFA fermentation (VFA –> hexose –> ?)

Answer 22

• acetate
• proprionate
• butyrate

Question 23

what is the pka of VFAs

Answer 23

4.8

Question 24

at a pH of 6.8, most VFAs exist in what form?

Answer 24

dissociated form
uses the VFA/HCO3 exchanger for intracellular transport

Question 25

at pHs closer to the pKa of VFAs, how are VFAs absorbed

Answer 25

via diffusion ( [ ] gradient)

Question 26

acetate enters the Krebs cycle as ?

Answer 26

Acetyl-CoA

Question 27

propionate enters the Krebs cycle as?

Answer 27

Succinyl-CoA --> gluconeogenesis

Question 28

buturate gets converted into _______ and then enters the Krebs cycle as _______

Answer 28

Beta hydroxybuturate (ketone body) in the rumen epithelium enters Krebs as Acetyl-CoA

Question 29

the most important gluconeogenic substrate; major source of glucose

Answer 29

propionate

Question 30

if VFAs accumulate in the rumen, they lower ?

Answer 30

pH; favors microbes producing lactic acid

Question 31

A high amount of _______ generate large amounts of VFAs quickly

Answer 31

easily digestible CHOs (beets/apples/grain)

Question 32

how does pH affect microbial growth rate

Answer 32

each bacterial species has a pH range w/in which growth is possible; pH optimums

Question 33

explain Rumenoacidosis

Answer 33

* carbohydrate overload leads to increases VFAs and decreased pH * lactate production increases, further decreasing pH

Question 34

what are the symptoms of rumenoacidosis

Answer 34

unspecific but... variable appetite, decrease in milk production, D+, bloat, reduced rumen motility, increased HR and breathing rate, laminitis

Question 35

glandular digestion of microbial protein in the cow begins in the ?

Answer 35

abomasum via abomasal enzymes such as lysozymes it then continues in the duodenum w/ pancreatic enzymes

Question 36

what do lysozymes do

Answer 36

catalyze the hydrolysis of bacterial cell walls

Question 37

how does lysozyme production in ruminants compare to most mammals

Answer 37

* 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

Question 38

T/F: lysozymes are most active at low pH

Answer 38

true

Question 39

a measure for estimating how well a particular protein source is used

Answer 39

biological value

Question 40

what is the purpose of urea recycling?

Answer 40

ruminants recycle urea via saliva into the rumen for usage by bacteria that turn it into microbial protein

Question 41

aquaporins & urea transporter B are involved in ______ in ruminants

Answer 41

urea recycling

Question 42

what is the purpose of urea recycling in hindgut fermenters/nonruminants

Answer 42

it is a salvage mechanism that improves Nitrogen retention during times of protein deficit

Question 43

what determines the amount of microbial protein that reaches the small intestine

Answer 43

the amount of dietary crude protein & metabolic demand

Question 44

what determines the amount of plasma urea in a ruminant

Answer 44

the amount of microbial protein that reaches the SI & the presence of excess ammonia

Question 45

where does ammonia get absorbed, where does it get detoxified

Answer 45

rumen detox in liver via urea cycle

Question 46

what causes an accumulation of ruminal ammonia

Answer 46

if the rate of ammonia production or ingestion of ammonia exceeds the microbe's ability to utilize it to form amino acids

Question 47

what is urea poisoning / ammonia toxicosis

Answer 47

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

Question 48

what anatomical structure diverts the flow of milk into the abomaum of a fetus

Answer 48

esophageal groove

Question 49

explain rumen drinkers

Answer 49

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