Absorption of VFA 70% of VFA absorbed from rumen-reticulum 60 to 70% of remainder absorbed from omasum Papillae are important – provide surface area Absorption from rumen is by passive diffusion Concentration in portal vein less than rumen VFA concentrations Rumen 50 - 150 mM Portal blood 1 - 2 mM Peripheral blood 0.5 - 1 mM Absorption increases at lower pH H + + Ac - HAc Undissociated acids diffuse more readily At pH 5.7 to 6.7 both forms are present, however most is dissociated At higher pH, 1 equiv of HCO 3 enters the rumen with absorption of
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Absorption of VFA 70% of VFA absorbed from rumen-reticulum 60 to 70% of remainder absorbed from omasum Papillae are important – provide surface area Absorption.
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Absorption of VFA
70% of VFA absorbed from rumen-reticulum60 to 70% of remainder absorbed from omasum
Papillae are important – provide surface area
Absorption from rumen is by passive diffusionConcentration in portal vein less than rumen
Lower Energy Value of Roughage Compared with Grain
- Less digested- Lignin limits digestibility of digestible fiber
- Greater energy lost from fermentationCH4 Heat
- Increased rumination Rumen contractions Chewing- More bulk in digestive tract
Comparative Prices of Corn and Alfalfa Hay
NEg
Mcal/kg
$/ton DM
$/Mcal
NEg
Corn 1.55 121.75 0.0864
Alfalfa hay 0.68 75.00 0.1213
Requirements for GlucoseRuminants
1. Nervous system Energy and source of carbon
2. Fat synthesis NADPH Glycerol
3.Pregnancy Fetal energy requirement
4. Lactation Milk sugar - lactose
Sources of Glucose CarbonRuminants
Ruminants dependent on gluconeogenesisfor major portion of glucose
Sources of glucose in metabolism1. Propionate2. Amino acids3. Lactic acid4. Glycerol5. Carbohydrate digestion in intestine
Absorption of glucose from intestine
Glucose Synthesis
Acetate Amino acidsKetone Acetyl CoA Bodies
FattyButyrate acids
CitrateGlycerol
Acetyl CoALactate CO2 2 CO2
Pyruvate OxaloacetatePEP
Glucose SuccinateProteins Amino acids
Propionate
Conservation of GlucoseRuminants
1. Glucose not extensively used for synthesis of long-chain fatty acids in adipose of ruminants
- Not clear why glucose carbon is not used- Glycerol is needed for synthesis of triglycerides - Comes from glucose- Acetate supplies carbon for fatty acid synthesis
2. Low hexokinase activity in the liver3. Ruminants have low blood glucose concentrations
- Low concentrations of glucose in RBC
Consequences of Inadequate Glucose in Metabolism
1. Low blood glucose2. High blood ketones3. High blood concentrations of long-chain fatty acids (NEFA)
• During the last month of pregnancy• Ewes with multiple fetuses• Inadequate nutrition of ewe• High demands for glucose by fetuses• Low blood glucose and insulin• Mobilization of body fat• Increase in nonesterified fatty acids in blood• Increased ketone production by liver
Fatty Acid MetabolismRelation to Glucose
Diet fat Adipose Diet CHOH CO2 Acetate
Malonyl CoA
LCFA NEFA AcetateCO2
Glycerol LCFA acyl CoA 2 CO2
Triglycerides
Carnitine
FA acyl carnitine Malonyl CoA inhibits CO2 (Mitochondria)
Ketones
Low Blood Glucose and Insulin
• Increased release of nonesterified fatty acids from adipose.
• Less synthesis of fatty acidsReduced malonyl CoA
• Reduced sensitivity of carnitine palmitoyl- transferase-1 to malonyl CoA
Increased transfer of fatty acids intomitochondria for oxidation
• Increased ketone production
Fatty Acid Oxidation
FA acyl CoAAcetyl CoA
CO2
Acetoacetyl CoA
Acetoacetate (Mitochondria)
3-OH butyrate
FA acyl carnitine
Carnitine CoA
Low Milk Fat
Cows fed high grain diets:
Reduced milk fat percentage
Early theoryLow rumen pHShift from acetate to propionate productionIncreased blood insulinDecrease in blood growth hormone
More recent theoryIncreased production of trans fatty acids inthe rumenTrans fatty acids reduce milk fat synthesis
Long-Chain Fatty Acid SynthesisRuminants
Synthesis is primarily in adipose or mammary gland – Limited synthesis in the liver
Ruminants conserve glucose supply – Glucose not extensively used for long chain fatty acid synthesis
Most of carbon is supplied by acetate
Some butyrate used in mammary gland
Glucose metabolism supplies some of NADPH needed for fatty acid synthesis