fibre and monogastric Flashcards
The Role of Dietary Fibre
- Fibre impacts gut health, immune system & systemic health
- Maintenance of health
- Disease prevention
- Therapeutic applications in treatment of certain diseases\
- Too little or too much -> negative effects**
The Role of Dietary Fibre
- ‘Total’ dietary fibre directly interacts with & affects:
- Gastrointestinal tract health & function
- Dry Matter Digestibility
- Energy & nutrient utilization
- Satiety & food intake
- Glycemic response
- Immune function
- Gut microbiota
Gut microbiota depend on dietary fiber for:
- Energy source to sustain or shift gut microbe populations
- Produce some essential nutrients for host (e.g. vitamin K)
- Produce substances that act locally &/or systemically via
the immune or nervous systems & other organs
dietary fibre DF
- Indigestible plant & non-plant materials can act as dietary ‘fibre’
- Naturally derived, extracted forms or synthetic substances
- Potential origin from plant, fungi, or animal
dietary fibre to animals
- Unified by resistance to animals’ digestive enzymes
- Incapable of hydrolyzing (breaking) some chemical bonds
- However, not uniform in form or function
- Most complex category of food product
- Affects health
if Animal Enzymes Can’t Digest It…
What Happens to Fibre After Ingestion?
- Interacts with GIT & other digesta
2 Some forms pass through GIT
unchanged -> excreted in feces
* Some forms utilized by gut microbes
& disappear (partially or entirely) -> metabolites of fermentation appear
What is Fermentation?
- Metabolic process by which micro-organisms extract energy (ATP) from foodstuffs by creation of new substances
- Successful fermentation depends on presence of specific microorganism with the
correct substrate in a favorable environment
Fermentation of Fibre in Animals
- As fibre is fermented, composition of digesta/feces alters:
- Metabolites from fermentation increase
- As fibre disappears, fecal bulk decreases
- Microbiome may maintain or shift (competition)
- Microbial mass might increase
- In monogastrics, fermentation occurs in lower GIT:
- Determined by interaction between individual’s
microbiome & type(s) of fibre
Potential By-Products of Fermentation
- Amino acids
- Vitamins
- B vitamins (varies with species)
- Vitamin K
- Gases (e.g., methane)
- Short Chain Fatty Acids (SCFAs C2-C6)
*AKA: Volatile fatty acids (VFA)
-Pairing of bacterial subspecies with specific fibre determines final products of fermentation
Short-Chain Fatty Acids (SCFAs)
- SCFAs -> chains of 2 – 6 carbons
- Acetate (C2)*
- Propionate (C3)*
- Butyrate (C4)*
**90-95% of SCFAs chould be these
Functions of SCFAs
- Source of Energy
- Act as signaling molecules
- Influence immune system
- Maintain or alter intestinal environment:
- Help maintain anaerobic environment
- ↑ tight junction proteins & mucin
- Acidify pH** in lumen of GIT/colon
- Helps inhibit growth of pathogenic microbes
- Ammonia trapping excrete in feces
SCFAs as Energy Source
- Herbivores - VFAs are major contributor to daily
maintenance energy (Calories) - Carnivores & Omnivores – negligible contribution
to daily maintenance energy; however, - Butyrate** is the preferred cellular fuel of enterocytes and colonocytes!
Fermentable Fibres Cons
- Insufficient fermentable fibre leads to:
- Decreased microbial diversity
- Impaired intestinal health
- Increased risk of colitis & obesity
fermentable fiber excess
Over-abundant fermentable fibre can cause:
* Abdominal distention/discomfort
* Increased/problematic flatulence
* Altered frequency of defecation
* Decreased fecal quality
Recommended to include in all diets
* Special emphasis in GI recovery diets
* Best type, blend, or amount differs between individuals
4 Main Descriptors for Dietary Fibre
Physiologically Significant Descriptors:
-viscosity: ability to form mucilages and gels
-fermentability: varies
Easily Measurable Descriptors:
-Solubility: Easy to measure in water
- Molecular weight – chain length
- Non-digestible oligosaccharides (NDO)
Viscosity
- Alters flow & mixing of digesta
** Slows gastric emptying & small intestinal transit - Can influence diffusion, digestion, &/or
absorption of nutrients - Viscosity dependent on:
- Concentration/amount of fibres present
- Conditions in the GIT
- Presence of other fibres
- Overall food matrix
Viscosity – Clinical Utility
Upper GIT
* Enhance satiety & decrease food intake
* Modulate post-prandial glycemic response
- Lower GIT – depends on fermentability
- If highly fermentable – ‘used up’ by gut microbiome
- If low fermentability – persists through transit of colon
- ‘normalize’ fecal consistency
- Potential drawbacks with increasing amounts
- Cause or exacerbate reflux
- Interfere with digestion
Insoluble Dietary Fibre (IDF)
- Does not dissolve in water
- High molecular weight
- Non-viscous
- Very low fermentability in non-herbivores
- ‘Bulking’fibre
- Laxation -> increased fecal output
- Dilute calories -> increased food volume
- Ex: Cellulose, hemicellulose, lignin
Soluble Dietary Fibre (SDF)
- Dissolves in water
- High molecular weight – SDF
- Adds some volume to food (less than IDF)
- Absorbs water
- May or may not alter viscosity
- All viscous fibres are soluble but not all soluble fibres are viscous!***
Oligosaccharides
- Dissolve in water; therefore soluble
- Often fermentable or ‘prebiotic’
- Physiologic effect from relatively small doses
- Not included in most fiber quantifications
resistant starches
- Resistant to digestion
- Physically inaccessible
- Altered structure
- 4 to 5 classifications of RS
- In upper GIT – functions like IDF
- In lower GIT – more like SDF
- Many RS are moderately to highly fermentable!**
- Most RS not included in traditional measures/quantification of fibre**
GIT different parts and absorption
Stomach
* Horses have relatively small stomach, dogs have relatively large stomachs
Small Intestine (SI) – main site for digestion/absorption of most nutrients
* Fibre influences how digesta is handled in small intestine but remains relatively
unchanged through passage
Cecum - Sac-like compartment at junction of ileum & colon
* Monogastric herbivores -> ‘Hindgut fermenters
Colon – main site of fermentation for non-herbivores although herbivores’ bigger.
* Highly fermentable fibres more quickly utilized in ileum & ascending colon, moderately -
slowly fermentable fibres may reach descending colon
hind gut fermenters
-monogastric herbivors
-* Relatively small stomach capacity
* Larger, complex ceca & colon
* ferments more fibres completely
* significant source of energy &
essential vitamins to herbivores
* 40-60% of calories for rabbits-horses
* Forage/grazing important for
* Preventing gastric ulcers & hunger
* Preventing dehydration
* fibre holds water reserve in gut
* Preventing torsions & colic
* ‘Gut fill’ is needed to maintain the normal location & function of gut
structural vs non structural carbs
STRUCTURAL
Supports plant as part of the cell wall
Cellulose (β 1,4 glucose linkage)
Hemicellulose (β 1,4 xylose linkage, other
monosaccharides used too)
Many branches and side chains
Lignin → phenol groups attached, almost
undigestable** DONT WANT TOO HIGH
Pectin (α/β 1,4 galacturonan linkage)
Structural or non-structural
NON STRUCTURAL
* Seeds, leaves, stems
* Energy source for plant:
* Simple sugars or starch
* Starch = multiple α 1,4 glucose linkage
* No side chains (amylose), with side chains
(amylopectin)
fibre
- Slowly digested structural material
- Cellulose, hemicellulose, lignin (not pectin)
- Essential to form the rumen mat (2 kg long hay/day)
-NDF and ADF
ADF acid detergent fiber
- cellulose, lignin
- Least digestible portion (↑ ADF = ↓ digestibility)
- Occupies space and limits food intake
- Too much fibre = ↓ feed intake = ↓ production
-dont want too much ADF makes it hard to digest so animal stops eating as rumen is filled up and decreases feed intake.
NDF = neutral detergent fibre
- hemicellulose, cellulose, lignin
- Digestible portion of fibre (3-12% / hour)
- will determine dry matter intake
non-fibre CHO
- Pectins, starch, sugar
- Take up little space in rumen
- Completely digested by
microbes - Also digested by mammalian
enzymes - Fermentation much more rapid, rumen pH will decrease. we want to slow this down to limit drops in pH
rations are made of grains and forages
common grains: corn, barley=higher in starch-> digest faster
- Common forages:
- Alfalfa hay: high fibre, moderate non-fibre
carbohydrates (NFC) - Grass hay: moderate fibre, moderate NFC
- Corn silage: moderate fibre, moderate-high NFC
- Barley silage: moderate fibre, moderate NFC
- Pea silage: higher [protein], lower [fat]
- Advantage of corn silage:
- Higher NFC due to corn grain
- Energy and fibre together!
CHO fermentation
-* Both structural and non- structural CHO fermented
* CHO enzymatically degraded to monosaccharides
* Monosaccarides then
broken down to VFA (+ ATP)
VFA make
- Acetate = 2-C, propionate = 3-C,
butyrate = 4-C
-proprionate becomes glucose in the citric acid cycle ***
-acetate= milk fat
-higher fiber= more acetate =more milk fat
-high starch (grain) =more proprioate =more glucose, need to get fibre/ starch ratio right in dairy cows. - VFA can be used to make amino acids
or fatty acids for the microbes
metabolism of VFA
Delivered from rumen to liver by portal vein
* Β-hydroxybutyrate used by most tissues for energy
Propionate (and lactate) removed by the liver
Propionate → oxaloacetate (4-carbon), then to glucose
Lactate → pyruvate, then to glucose
Only SCFAs that can form glucose
Acetate will form acetyl-coA
Acetyl-coA + oxaloacetate = citric acid (for citric acid cycle)
Also used in fatty acid production
optimizing rumen fermentation: starch and forage
STARCH:
-Digestion can be improved by grinding, rolling, high moisture, steaming, flaking, cooking ( ↑ Surface area, digestibility)
-small amounts could go to SI, whole grains fed can slip out of rumen undigested.
FORAGE:
-fibre length is critical
0long stem is critical for rumen fibre mat, but ration sorting can occur
long stem fibre has: slower passage, lower feed intake.
carbohydrate engorgement (grain overload, ruminal acidosis)
Rapid intake of grain
* Grain processing increases surface area for bacterial
fermentation = more rapid VFA, lactic acid production
* Amylolytic bacteria (e.g. Streptococcus bovis) ferment
grain fastest
* Lactic acid as byproduct, D-lactate accumulates in rumen.
-low pK= stronger acid than VFA
Lack of fibre = ↓ chewing, regurgitation, salive and less buffers
* Rumen pH drops
* Lactobacilli thrive and produce more lactic acid
* Protozoa die – starch granules released
ketosis mech
-FFA are mobilized and transported to the liver, acetyl coA is usually oxidized in TCA cycle. rate limmiting step is = oxaloacetate (from propionate)
* Incomplete oxidation to ketone bodies,
- Ketones:
- β-hydroxybutyrate: most common in
cattle - Acetoacetate
- Can be used as energy source, not by the brain
- Suppress appetite
clinical signs of different ketosis
Wasting ketosis:
* Clinical or subclinical
* Decrease in appetite → Body weight loss →
Decreased milk production
* Ketones on breath
- Nervous ketosis:
- Acetoacetate → brain → isopropanol
- Alcohol and hypoglycemia
- Circling, straddling/crossing legs, head pressing, delirium
- Pregnancy toxemia (small ruminants)
- Late pregnancy
- Very similar to nervous ketosis 26
feed impactions
- Off-feed, poor-quality roughage
- Prolonged feed breakdown
- Rumen impacted
- Poorly digested feed escapes to
abomasum - Abomasal impaction
