Rumen Motility and Rumination

Describe the arrangement of digestive material inside the rumen?

• Top - gaseous layer

• Middle - solid fiber mat

• Bottom - liquid layer

How does a ruminant eat?

Mastication

• Prehension

• Mastication

• Insalivation

Deglutination

• Swallowing

Rumination

• Regurgitation

• Re-mastication

• Re-insalivation

• Re-deglutination

Eructation

• Evacuation of gas in association with regurgitation

How much time per day is devoted to ruminating in sheep and gotas?

~8 hours

Rumen contractions are cyclical, they can be divided into what three phases?

1.) Primary mixing contraction

2.) Secondary eructating contractions

3.) Rumination contraction (Ancillary to the primary contraction)

What do the rumen contractions function to do?

1.) Facilitate the mechanical breakdown of plant material, exposing a larger surface area to microbial fermentation

2.) Allow the elimination of fermentation gases through eructation

3.) Facilitate ruminal buffering by re-insalivation (Cud chewing)

4.) Mix the ingesta with ruminal digesta thereby exposing fresh digest to microbes

Describe the primary (mixing) contraction process.

Occur every 40-60 seconds

1. Biphasic reticular contraction (Proximal and caudally)

   1. Pushes large particles into the rumen mat, small particles enter the cranial sac and some may exit via reticulo-omasal orifice, and some digesta is regurgitated

2. Cranial Sac Contraction

   1. Everything pushes into dorsal sac

3. Dorsal Sac contracts

   1. Mixing it in dorsal sac

4. Caudo-Dorsal Sac Contraction

   1. Secondary release of gas, gas leakage

5. Ventral Sac Contraction

   1. Continues into the caudoventral blind sac

How does regurgitation occur during the first step of the primary (mixing) contraction?

At the same time as the biphasic reticular contraction:

• Thorax expands

• Larynx closes

• Antiperistaltic wave

• Masticate 40-50 times

Describe the secondary (eructation) contraction process.

Occurs every 120 seconds, does not occur with all primary contractions, reticulum does not participate

1. Caudo-ventral blind sac contracts

2. Caudo-dorsal blind sac contracts

   1. Pushing gas towards the esophagus

3. Ventral blind sac contracts from posterior to anterior

   1. Pushing gas up through esophagus, leading to eructation

What higher center inputs may stimulate reticulorumen motility?

• Milking

• Feeding

• Low environmental temperature

• Ingesta consistency - course fibrous increase

• Fibre length

What higher center inputs may inhibit reticulorumen motility?

• Chopped/fine diets are weak stimulators of motility

• High temperature (pyrexia)

• LPS (Polysaccharide on Gram - bacteria, which is toxic)

What gastric centers may inhibit reticulorumen motility?

• Pain

• Low pH (rumen stasis, grain acidosis)

• High activity of stretch receptors in abomasum decreases

What gastric centers may enhance reticulorumen motility?

• High stretch receptor activity within walls of rumen enhance motility

What are the four main bacteria phyla found in the rumen?

• Bacteriodetes

• Firmicutes

• Proteobacteria

• Spirochaetes

200 different genera

10^11 viable cells per gram of rumen fluid

What do protozoa do in the ruminant?

• 2 families

• Engulf and degrade plant material + bacteria within themselves

• Are fragile, could be lost due to feeding strategies with high concentrates, dropping pH

What do fungi do in the ruminant?

• 5 different genera

• Efficiently degrade lignocellulose and other structural carbohydrates

What affects the makeup of the ruminal biome?

• Regional differences

• Microbial community composition varies with diet and host, but a core microbiome is found across wide geographical range

Why do high starch diets have the potential to negatively affect ruminal fermentation?

• Increase the proportion of amylolytic bacteria

• Increase the overall concentration of VFA

  • Increase the concentration of butyrate, propionate, valerate

  • Reduce concentration of acetate, and acetate:propionate ratio

• Reduce daily average pH

• Increase amount of time ruminal pH below cut-off (5.8 or 5.6)

• Ruminal papillae degradation

Disease occurs if there is an imbalance of VFA production, absorption and buffering.