PDA II - Rumen

Contractions of reticulorumen

Primary contractions (mixing)

• Biphasic reticular contraction

  • 1st phase: Reduction of ½ of volume

  • 2nd phase: Content of reticulum transfered to cranial sac

• Contraction of rumen cranial sac (content move to dorso-caudal blind sac)

• Contraction of dorsal blind sac (ingesta move cranially)

• Contraction of the ventral rumen sac

Eructation

Secondary contraction, push rumen gaz outside

CHO metabolism

Except lignin (degradated by fungi)

1. Bacteria attaches to CHO, its membrane enzyme degrade the polymer in soluble sugars

2. Internally, fermentation by glycolysis soluble sugar into pyruvate

3. Anaerobic MO convert pyruva in VFA

VFA and roles

Propionate: Source of energy for milk sugar, only that can be converted to glucose after absorption

Acetate: Energy for muscles, milk fat and ATP

Butyrate: Energy for rumen wall + lypogenesis in liver

Which feed promote which VFA

Forage → acetate

Grains → propionate (more lactic acid)

Lipid metabolism

Diet in herbivore low in lipid: lipid reduce appetite, fermentation of cellulose and motility of forestomachs

Palmitic, oleic and linoleic are the most common

Hydrolyzed by MO enzymes in glycerol or galactose then fermented into VFA

Protein metabolism

For RDP:

1. MO membrane proteases break prot in small peptides

2. Peptides are absorbed by bacteria and converted into AA, some are used for synthesis of protein most are deaminated (=NH3 + VFA)

For AA synthesis bacteria need nitrogen and carbon backbone from carbs

Absorption in forestomach

Reticulorumen → blood:

• VFA (80% in rumen) by faciliated diffusion (exchanged with HCO3-) or simple difffusion

• Ions (Na+, Mg2+ = active) (K+ Cl- = passive)

Blood → reticulorumen:

• Urea

MO for protein

Proteolytic bacteria and protozoa