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Nutrition and Digestion > Lecture 7- VFAs and digestion > Flashcards

Lecture 7- VFAs and digestion Flashcards

1
Q

What is the main fuel the rumen makes?

A

VFAs

-ruminants do not use glucose like we do

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2
Q

What are the three main VFAs?

A
  • Acetic= mainly as energy source
  • Propionic = for lactate production
  • Butyric= same as propionic
  • Acetic, propionic and butyric are the predominant forms
  • Generally ~ 75:15:10 to 40:40:20
  • Weak acids (pK
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3
Q

What are the VFAs?

A 
• Volatile Fatty Acids (VFA’s)
• Also called short chain fatty acids (SCFA’s)
• Produced during microbial fermentation • Acetic
• Propionic • Butyric
• Formic
• Isobutyric • Valeric
• Isovaleric
• 2-methylbutyric • Hexanoic
• heptanoic)
-all produced in the rumen
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4
Q

What is the main energy source for ruminants?

A

• In the 1940’s researchers (mainly from Cambridge) demonstrated that most
of the feed consumed by ruminants is fermented
• Continuing work demonstrated that VFA’s are used by many tissues
• VFA’s are the main source of energy for ruminants
• Except for starch etc. that are digested in the small intestine • Acetate mainly energy
• Propionate contributes to energy, lactate and CO2
• Butyrate contributes to 3-hydroxyl butyrate, CO2 and energy
-the animal use VFAs in

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5
Q

PIC1What are the concentrations of VFAs in different parts of the animal in different animals?

A
  • sheep and cow have it in the rumen

- hindgut fermenters like a horse have it caecum

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6
Q

What does the concentration of the VFAs depend on?

A
  • on the species and the diet

- particularly starch content depends

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7
Q

How are VFAs metabolised?

A
  • VFA’s are transported into the blood via the rumen epithelium • Some VFA’s are metabolised during this process
  • ~88% of VFA’s are directly absorbed by the rumen • ~12% make it into the omasum
  • VFA’s not absorbed by the rumen are metabolised by the liver
  • REMEMBER glucose is NOT absorbed in the digestive tract of ruminants although tissue requirements for glucose are similar to that of other species
  • The gut itself is the major consumer of glucose (and the mammary in lactating animals)
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8
Q

What is the liver’s and portal blood flow’s function in digestion?

A
  • the portal vein supplies the liver (from the digestive tract)
  • here the VFA’s are made into glucose and can be used
  • when fed, right after get an increase in portal blood flow
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9
Q

What is special about the digestion of starch?

A

-can get glucose from starch directly in the small intestine
• Starch is the exception and glucose can be directly absorbed from starch sources by the small intestine
• E.g. maize or other grains
• Manipulations of starch to ensure it bypasses the rumen is possible
• Commercial products are available
• This increases the glucose supply and can prevent acidocis
-if you can manipulate the starch so it bypasses the rumen can control how much glucose the animal has

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10
Q

What is propionate turned into and where?

A
  • glucose in the liver
  • B12 coenzyme is very important for this
  • the conversion is energetically costly
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11
Q

What is the acetate metabolism in ruminants?

A

• Ruminants absorb more acetate than glucose into the blood
• Therefore there are differences in ruminants and non-ruminants in
how acetate and glucose are used as precursors for acetyl-CoA • For later use in oxidation or lipogenesis etc.
• In ruminants, only a small amount of acetate uptake in the liver is low • But the liver does produce acetate
• In ruminants (& pigs) the majority of lipogenesis occurs in adipose tissue
• Unlike humans and birds where it occurs in the liver
• This is related to the metabolism of acetate as Acetyl-CoA is readily used for fatty acid synthesis
-glycolisis happens in the adipose tissue as opposed to humans

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12
Q

What is the propionate and butyrate metabolism like in ruminants?

A

• Metabolised by both the rumen & gut epithelium and the liver
• Little propionate & butyrate is in the general circulation (unlike
acetate)
• Propionate is the main glucose precursor in the liver
• Liver is glucose factory with little need for or capacity to absorb glucose
• Butyrate → butyryl-CoA → acetyl-CoA → long chain fatty acids or
ketone bodies
• In peripheral tissues butyrate is rapidly oxidized or used in lipogenesis
• Or removed by the mammary for milk fat synthesis
• Propionate → 5 steps → glucose (TCA cycle)

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13
Q

What is the main glucose precursor in the liver?

A

• Propionate is the main glucose precursor in the liver

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14
Q

What are some of the reactions that happen in the rumen?

A

-production of VFA and methane as well as many other substances (acetate, lactate etc,)

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15
Q

What are the functions of acetyl co-A?

A

-used differently in the liver, muscle and adipose tissue

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16
Q

What is the importance of digestive kinetics in ruminants?

A

• When a feed particle enters a site of digestion/degradation (e.g. the rumen), it can only leave by one of two mechanisms
• Fermentative digestion (ranges from 61 to 85% of OM)
• Passage from the site
• These two processes compete with each other – rapid rate of passage = lower potential degradation
-if something passes through rapidly then the animal will have little time to ferment it than if have more time in the rumen

17
Q

What are the factors influencing the rate of passage (ie VFA production)?

A

• Increasing the rumen passage rate will decrease total VFA production
• Associated with reduced DM digestion
• On a given diet, increasing the liquid dilution rate will:
• Increase the production and concentration of acetic acid, butyric acid and methane
• Decrease the production and concentration of propionic acid
-propionic is the most important one for glucose!

18
Q

What is BMR (basal metabolic rate) important for and how can you establish it?

A
  • Limitations:
  • Requires fasting
  • This is difficult in ruminants (humans = overnight, birds = 2 days, ruminants & pigs = 4 days).
  • Indicators of fasting include a decline in heat production to a steady state, respiratory quotient (0.7 which indicates energy is being obtained from body reserves)
  • Needs a state of complete relaxation
  • Hard to obtain in animals
  • Standing Vs lying can increase heat production
  • May be more accurate to call ‘fasting metabolism’

-fasting takes 4 days
-get heat production from breathing
-

19
Q

What is heat production related to?

A
  • Fasting heat production is more closely related to the surface area of an animal than its weight
    • This is difficult to measure
    • Thus animals are compared by expressing them in relation to their surface
    area (SA)
    • SA is proportional to 2/3 bodyweight, Thus W0.67
    • In reality it is closer to W0.73
    • Rounded to W0.75
20
Q

What is digestibility?

A

-• Nutrient analysis of feeds does not tell us:
1. Efficiency of utilisation of nutrients 2. Chemical integrity of nutrients
3. Acceptability (intake)
• Not all the nutrients present in food are available for metabolism.
• Digestibility  most important determinant of nutrient availability, or feeding value of feeds
• Measure of efficiency of digestion and absorption of nutrients present in food
• Expressed as either as a percentage (digestibility coefficient), a proportion or g/kg DM
• Dry matter (DM) digestibility is calculated as:
-DM dig (%) = (DM intake - DM faecal/ DM intake) x100

21
Q

What are the nutrients in facese?

A
  • Nutrient excreted in faeces; • Undigested food residues
  • Body tissue residues (enzymes, damaged cells from GI tract lining, gut microorganisms)
  • Types of digestibility
  • Apparent digestibility  not corrected for endogenous losses
  • True digestibility  corrected
22
Q

What is an apparent and true digestibility?

A
  • Appdig (%) =(Nutrient intake - Nutrient output/ Nutrient intake) x100
  • True dig (%) = (Nutr. Int - (Faecal Nutr.  Endog. Nutr.)/ Nutr. Int.) x100
  • Endogenous nutrients =body tissue residues
  • True digestibility > Apparent digestibility
23
Q

What are the animal factors influencing digestibility?

A
  • Age of animal
  • Underdeveloped enzyme systems or digestive organs in young animals
  • Loss of competence with age e.g Lactose intolerance • Species of animals
  • Ruminants better able to digest fibre than non ruminants
  • Sheep digest grains more efficiently than cattle, while the reverse is true for forages
24
Q

How does food composition affect digestibility?

A
  • Digestibility is related to chemical composition
  • Cellulose less digestible than starch
  • Lignin content impinges on digestion
  • Deficiencies or excesses of other nutrients in the diets
  • N & S deficiencies, restrict microbial growth in the rumen and reduce fibre digestibility
  • Excess dietary fat in the diet (> 5%) inhibits rumen micro-organisms and fibre digestion
25
Q

What is meant by associative effects on digestibility?

A
  • Some foods are less digestible when consumed in conjunction with other foods than on their own
  • Associative effects are negative (digestibility of mixed rations is less than expected)
  • In ruminants, digestibility of forages is poorer when they are fed in conjunction with starchy feeds
  • Starch is rapidly fermented producing lots of VFA that lower pH inhibiting cellulolytic bacteria
26
Q

How does preparation of food affect digestibility?

A
  • Heat treatment
  • Boiling potatoes increases starch digestibility
  • Destroys trypsin inhibitors e.g. soyabeans • Maillard product formation
  • Chemical treatment of forages
  • Forages = grinding reduced rumen digestibility by 20%
  • increase intake and outflow, reduces exposure time to enzymes • Grains  crush for cattle, grind for pigs
27
Q

How can you affect digestibility with enzyme supplementation?

A

• Non-ruminants are not well equipped with enzymes to digest many constituents of foods
• Enzyme preparations added to diets e.g.
• beta-glucanase = destroys glucans poultry in feeds (they interfere with digestion
of other nutrients)
• Phytase = destroys phytic acid, increases availability of P • Cellulases =-linked glucose from cellulose
• Proteases = breaks down proteins

28
Q

How does level of feeding affect digestibility?

A
  • Feeding levels
  • Maintenance = no gain or loss in body weight
  • Describe as multiples of maintenance
  • increase quantity of food consumed, increase rate of passage through the gut
  • reduced digestibility is due to shorter duration of exposure of ingested food to enzymes
29
Q

What are some anti-nutritional factors?

A
  • Substances that inhibit enzymes or impair to nutrient utilisation • Tannins = bind to proteins and amino acids
  • Trypsin inhibitors = impair trypsin activity
  • Maillard products = reduced protein & CHO digestion
  • Aflatoxins = toxic, also erode gut lining
30
Q

How can pig’s digestion be affected by time?

A
  • wheat is rapidly digested
  • others digested more slowly
  • Diet composition can alter transit time in the gut in the pig
31
Q

What drives & limits intake in ruminants?

A
  • Extremely complex!
  • We have discussed some of them • Distention
  • Gut fill
  • Metabolic signals are less understood in ruminants
  • Fuel types differ between monogastrics and ruminants (who consume less fat and more fibre)
  • Fermentation means that the type and supply of fuels is different in ruminants
  • Some satiety factors are independent of feeding behaviour& others are integrated through their effects on metabolism
  • Growing consensus that fuel-based sensing of tissues contributes to the control of intake in ruminants
  • Temporal mechanisms in control of intake can have effects that last from minutes to months
  • Long term mechanisms that influence maintenance include hormones and cytokines like leptin & TNFα
  • Fuel oxidation influences feeding behaviour
  • Signal from the liver can be stimulatory or inhibitory
32
Q

What are some inhibitory signals and stimulatory signals?

A
  • in ruminants these are as follows:

- nhibitory signals (distention etc.) wane &stimulatory signals increase following meals

33
Q

What is the hepatic oxidation theory?

A

-theory that liver drives the satiety and digestion in ruminants, contentious

34
Q

What are some other theories?

A
  • Direct nutrient sensing by peripheral and metabolic tissues?
  • Different influences of protein vs. fat. vs. carbohydrate
  • Specific receptors
  • Particularly in splanchnic tissues
  • E.g. G-coupled receptors & glucose receptors
  • Role of the CNS?
  • Role of the small intestine?

Nutrition and Digestion (24 decks)

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