Carb absorption
VFA absorption happens by?
Primarily absorbed through rumen epithelium - smaller proportion in omasum and SI
rumen papillae - surface area
Absorption rate proportional to size of VFA - Butyrate > propionate > acetate
Ionized VFAs can pass through rumen epithelium, must be unionized to pass into blood vessels, CO2 diffusion into epithelial cells
Common nitrogen sources are?
True proteins - 60-80%
Nuclear proteins - 10%
Non-protein nitrogen - 5-60% = ammonia and ammonium salts, urea, amides, amines, uric acid
bacteria nitrogen metabolism
Deaminate amino acids - ammonia + carbon skeleton, use carbon skeleton for energy
Amino acids made into microbial protein
Synthesize amino acids from ammonia and carbon skeleton
Feeding supplemental fat to? or types?
Palm oil cake - high NDF fat source, acts like fiber source with fat added
Increased milk fat - mechanism not clear
Controversial ingredient - deforestation for palm oil production
Fat absorption
No long chain FA are absorbed in the rumen - only VFA
Similar mechanisms are monogastric fat digestion - emulsification by bile salts
Pancreatic lipase is less important - majority of lipids are microbial or FFA
Absorbed into SI mucosa - Packaged in chylomicrons, lacteals -> lymphatic circulation
Lactic acid absorption
Small quantities can be absorbed by the rumen
very slow - 10% of the absorption rate of VFAs
Reason = stronger acid - lactic acid has much lower pKa, more ionized at moderate rumen pH, gain overload
What is rumen Degradable protein? (RDP)
portion of protein degraded by rumen microbes, only half of total crude protein, bacteria (only 10-40% of species will degrade proteins), protozoa (can utilize dietary protein, generally consume bacteria for protein instead)
Non-protein N
Can feed up to 30% of total diet N as NPN
Problems with going to high - palatability, reduces microbial growth -> protein synthesis, energy cost to convert absorbed NH3 to urea
Ammonia toxicity - bovine bonkers, incoordination, salivation, tremors
treatment - NH3 is rapidly absorbed from rumen but NH4+ is not, acidic pH = more NH4+ than NH3, stomach tube with vinegar
Hydrolysis is?
Cleaves ester linkages to glycerol
produces free fatty acids
85% occurs extracellularly
primarily performed by bacteria
inhibited by: high fat content in diet, low rumen pH, ionophores
Body fat composition
Monogastrics = more unsaturated FA, unsaturated FA in cis isomer, even chain FA
Ruminants - More saturated FA, unsaturated FA in cis and trans isomers, odd chain FA, branched chain FA
Electrolyte absorption
Cl- moves from rumen to bloodstream - pulled by electrical gradient, moves against concentration gradient
Na+ moves from rumen to bloodstream - against both electrical and concentration gradient
K+ moves in both directions - no net difference
Water moves with osmolarity - goes to high solute concentration = normally from rumen to bloodstream
What is rumen undegradable protein (RUP)?
Dietary protein not digested by microbes - bypass protein
Sources - certain natural products (dehydrated alfalfa, blood meal), processed protein is treated to protect from microbes (heat treatment, fat encapsulation, formaldehyde denaturation, mineral chelation
Digested by animal in the SI
CHO and N balance
Optimize microbial protein synthesis
requires 3 inputs present at the same time - energy, carbon skeleton, N
Rapidly fermented CHO - require rapidly available N
Slowly fermented CHO - require N that is more slowly digested
Biohydrogenation is?
conversion of unsaturated to saturated FA - add H to double bond, reductase
Saturated FA less toxic to bacteria
~15% unsaturated FA are bypass - escape biohydrogenation in rumen
Rumen pathologies
Carbohydrate engorgement = grain overload
Sub-acute ruminal acidosis
Bloat
Displaced abomasum
Nitrate poisoning
VFA metabolism
Blood from rumen enters portal vein -> liver
metabolism by liver = butyrate -> b-hydroxybutyrate (energy source for most tissues), propionate (gluconeogenesis, only SCFA that can form glucose), Acetate -> acetyl-CoA (enters TCA cycle - ATP production, fatty acid synthesis)
Produces majority of ruminants energy (20-80%)
Hind gut fermenters = VFAs less important as an energy source
Bacteria AA synthesis?
Ammonia + carbon skeleton -> amino acid
requires energy
Transamination - transfer of amino group from one carbon skeleton to another, can convert non-essential AA to essential AA
Lipids in the diet?
Comprise a small portion of the diet - 1-10% of DMI
Plant lipids = leaves, waxes, seeds
Usually unsaturated fatty acids - contain double bonds, mostly i the cis isomer
Other microbial metabolism?
Isomer change - cis->trans = more stable, higher melting point
Chain lengthening - add acetate = 2 C to chain
Odd chain FA - odd number of C
Branched chain FA - benefits for heart disease and diabetes
What is nitrate poisoning?
Excess nitrates in feed - drought stress, frost damage, over fertilizing
Bacteria convert nitrate to nitrite - more toxic
Normally nitrite is converted to ammonia
high levels = absorption into blood
Binds to hemoglobin to form methemoglobin - reduces O2 carrying capacity, blood turns chocolate brown colour
Net energy to the animal through carbs?
Non-structural CHO - sugars, starch, pectin = little direct absorption by animal, microbial fermentation to VFA
Structural CHO - cellulose and hemicellulose = microbial digestion to monosaccharides, monosaccharides fermented to VFA, energy not available to animal without microbial breakdown
Ammonia sources? and absorption?
Sources = Non-protein N from feed (nitrates, urea, ammoniated straw), or urea recycling (diffuses from blood into rumen, secreted in saliva)
Absorption = excess ammonia in rumen is absorbed, converted to urea by the liver, excreted by kidneys, diffuses from blood into milk
Fats in the diet?
Fats are high in energy but.....
low palatability
fat can coat feed material - not accessible to bacteria to ferment = decrease VFA production, bypass protein/AA/vitamins
Long-chain fatty acids are toxic to bacteria - especially unsaturated Fa
milk fat depression - inhibited by a type of trans FA
Feed can go rancid
Microbial lipid use?
Bacteria = not used for energy production, synthesis of cell membrane, inhibits methane production
Protozoa = Consume and hoard unsaturated FA, released when protozoa are digested in SI, FA remain unsaturated Cis isomers
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