ch. 15.2: fermentation in the ruminant

what are the 9 reasons that the rumen is a favorable place for microbial growth?

1) warm (101-105 degrees F)

2) moisture

3) daily food supply from animal eating

4) pH controlled (saliva)

5) dark (no UV damage)

6) mixing (reticulum)

7) no oxygen

8) end products are removed (absorbed or passed)

9) rumination occurs to decrease particle size

what microbial species are present in the rumen and at what levels?

1) bacteria

• vast number (15-50 billion per mL) & digest nutrients

2) protozoa

• 35 species, 20k-500k per mL, prey on bacteria

3) yeast (fungi)

• small amount, help w cellulose breakdown

what is the total microbial population in the rumen?

2.5 × 10^15 microbes

what are the end products of fermentation for starches and fibers?

VFAs

what are the end products of fermentation for proteins

ammonia (NH3) and then microbial proteins

what are the end products of fermentation for ammonia

microbial protein

what are the end products of fermentation for unsaturated fats?

saturated fats

what are the 6 total end products of fermentation

1) VFAs

2) microbial protein

3) ammonia

4) lipid alterations

5) gas

6) heat

what are the 3 types of VFAs

1) acetate/acetic acids (2 carbons)

2) propionate/propionic acid (3 carbons)

3) butyrate/butyric acid (4 carbons)

what types of feed impact CHO and VFA fermentation and concentration?

concentrate diets (grain):

• high starch, more VFA’s produced

• lower pH in rumen

• makes more propionate (2:1 ratio instead of 3.5:1 for acetate: propionate)

forage diets:

• high cellulose, lower VFA’s produced

• higher pH in rumen

what is an ionophore?

• feed additive to shift MCO into propionic-producing species

• common trade names: Rumensin and Lasalocid

• animal response: improved feed efficiency or average daily gains

what determines the fate of a dietary protein?

1) what type it is (escape/bypass rumen or soluble)

2) rate of fermentation

3) rate of passage (how fast does it leave the rumen?)

how are urea, protein, and amino acids digested in the rumen?

since they are nitrogen sources, they are broken down into ammonia and a carbon skeleton, which can be combined to form a MCO protein that can pass thru the abomasum and rest of the digestive tract

• or the carbon skeleton can be digested to produce VFA’s

what is the crude protein percent produced by microbial digestion?

MCO protein contains ~50% CP

what vitamins are produced by microbes in the rumen?

B vitamins and vitamin K

what is the process of NH3 that is produced during fermentation?

1) byproduct of the deamination of amino acids

2) mostly gets incorporated into the MCO protein but can also be absorbed through the rumen wall

3) can also go through nitrogen recycling or exit the body through urination

how do excessive fat levels impact fiber digestion?

if fats become >10% of the diet, then the feed would get coated and hinder MCO attachment and degradation of cellulose