Rumen carbohydrates Flashcards
Carbohydrates in a ration
-70-80% of typical ration dry matter
-supplies 60-70% of net energy to animal upon digestion
Types of carbohydrates
- structural CHO
- non structural CHO
Structural CHO
*supports plant as part of cell wall
-cellulose
-hemicellulose
-pectin
Cellulose
beta 1-4 glucose linkage
-forms long linear strands arranged in parallel
Hemicellulose
beta 1,4 xylose linkage
-many branches and side changes
-includes lignin
Pectin
alpha/beta galacturonan linkage
-structural or non structural
-cements plant cell walls
Non structural CHO
-seeds, leaves, stems
-important energy source for plants (simple sugars or starch)
Starch
Multiple alpha 1,4 glucose linkages
-no side chains (amylose)
-side chains (amylopectin)
Fibre
Slowly digested structural material
-includes cellulose, hemicellulose, lignin (not pectin)
-forms the rumen mat
NDF
Neutral detergent fibre
-hemicellulose, cellulose, lignin
-digestible portion of fibre (3-12%/hr)
-determines dry matter intake
ADF
Acid detergent fibre
-cellulose, lignin
-least digestible portion (increased ADF=decreased digestibility)
-occupies space and limits food intake
-too much fibre= decreased feed intake and production
Non-fibre CHO
-pectins, starch, sugar
-take up little space in rumen and are completely digested by microbes and mammal enzymes
-fermentation very rapid (4-8%/min instead of /hr)
Non-fibre CHO and rumen pH
Balance out intake because non-fibre CHO will decrease rumen pH
-disrupts rumen microflora= rumen acidosis
Common forages
1.alfalfa hay
2. grass hay
3. corn silage
4. barley silage
5. pea silage
Alfalfa hay
-high fibre, moderate non fibre carbohydrates
grass hay
moderate fibre, moderate NFC
Corn silage
moderate fibre, moderate-high NFC
Barley silage
-moderate fibre, moderate NFC
Pea silage
lower protein concentration, higher fat concentration
Advantages of corn silage
-higher NFC due to corn grain
-energy and fibre together
What are the most common feedstuffs?
-barley
-corn
Fermentation
-both structural and non structural CHO are fermented and than degraded into monosaccharides
-monosaccharides broken down into the VFA + ATP and liver
VFAs
-acetate (2C)
-butyrate (4C)
-proprionate (3C)
Different species of involved in fermentation
Other than VFAs, what else are products of fermentation? Who uses these?
-lactate (can become glucose)
-other short chain fatty acids
*used by secondary bacteria
What are VFAs used for?
Used to make amino acids or fatty acids for microbes
What are beta-hydroxybutyrate used for?
Used by most tissues for energy AND used as initial carbon skeleton for FAs in milk
Use of proprionate
Forms oxaloacetate, then GLUCOSE
**only one that can be used to make glucose (other than lactate)
Use of acetate
- Forms acetyl coA
-acetyl-coA +oxaloacetate= citric acid - used in fatty acid production
What competing priorities are involved in optimizing rumen fermentation?
-energy requirements for milk production
-milk fat
-animal health
Improving starch digestion
Improved by grinding, rolling, high moisture, steaming, flaking, cooking
*increased surface area and digestibility
Difficulties eating starch
-cattle cannot chew whole grains, sheep and goats can
-small amounts of starch and whole grain can sometimes slip through= indicates undigested and therefore unused by animal
Forage/fibre length
Critical= long stem fibre needed for fibre mat
*but if too much in ration, then the cattle will sort it out and pick what they get to eat= disruption of stable rumen
Balancing long stem fibre
-slower passage through rumen
-lower feed intake
Grain overload
-rapid intake of grain
-grain=more rapid VFA= lactic acid
*amylolytic bacteria (Strep bovis) ferments grain fastest
-D-lactate accumulates in rumen=lower pH
-Lack of fibre= decreased chewing, regurg, saliva and less buffers = lower pH
-Lactobacilli thrive= more lactic acid
-Protozoa die= starch granules released
Ketosis
- FFA mobilized, transported to liver
- Should be used to make acetyl-CoA; rate limiting step=oxaloacetate which needs propionate (which we are lacking)
- Results in production of beta-hydroxybutyrate and acetoacetate instead
- Results in some tissues using them, and get suppressed appetite
Wasting ketosis
-clinical or subclinical
-decreased in appetite = body weight loss = decreased milk production
-ketones on breath
Nervous ketosis
Acetoacetate goes to brain and forms isopropanol (alcohol) and hypoglycemia in brain
*results in circling, straddling/crossing legs, head pressing, delirium
Pregnancy toxemia (small ruminants)
-late pregnany
-similar alcohol and hypoglycemia in the brain
Impaction
- off feed, poor quality roughage
- prolonged feed breakdown
- rumen impacted
- poorly digested feed escapes to abomasum
- abomasal impaction
