Phys Eco Exam 1 Ruminants, Hingut fermentation, and GI Plasticity #5

What is the rumen?

The first and largest of the three parts of the ruminant fermentation chamber.

What is rumination?

Regurgitation of large fiber particles for further chewing.

Why does ruminant saliva contain NaHCO₃?

It acts as a buffer to maintain rumen pH.

What three major VFAs are produced by ruminant fermentation?

Acetate (2C), propionate (3C), and butyrate (4C).

How are acetate and butyrate used?

Both can be easily modified to enter the Krebs cycle.

What can happen to propionate?

It can enter the Krebs cycle or be converted back into glucose because it has an odd number of carbons (3C).

What other products result from rumen fermentation?

CO₂, methane (CH₄), ammonia (NH₃), microbial protein, and essential B vitamins.

What is the ruminant protein dilemma?

Food must be made small by microbes to leave the rumen → microbes require protein → plants are low in protein → limited protein limits microbes → limited microbes reduce digestion and ultimately intake.

What happens to plant protein consumed by rumen microbes?

Microbes produce microbial protein, which the host can use, and ammonia, which microbes can use.

How do ruminants recycle nitrogen?

They convert ammonia to urea and return urea to the rumen through saliva. They can also make urea from body protein.

Why is urea recycling beneficial?

It conserves a limited resource and maintains the microbial population

What is the ruminant glucose dilemma?

Rumen microbes consume essentially all plant glucose, but the animal still requires glucose for the CNS and metabolism.

How do ruminants deal with low glucose availability?

They tolerate low blood sugar, maintain low insulin so glucose is not readily converted into fat, and perform gluconeogenesis.

What is gluconeogenesis?

Production of glucose from non-carbohydrate sources.

What substrates can ruminants use for gluconeogenesis?

Propionate, amino acids, and glycerol.

Where does hindgut fermentation occur?

In the proximal colon or cecum.

What animals use proximal-colon fermentation?

Herbivorous lizards, equids, elephants, rhinos, and wombats.

What animals use cecal fermentation?

Rodents, rabbits, koalas, and some birds such as grouse and ptarmigan.

What are the advantages of hindgut fermentation?

Host digestion occurs first, giving the animal access to protein and glucose, and food can be pushed through faster.

What are the disadvantages of hindgut fermentation?

No rumination, limited nitrogen for microbes, and fermentation products are produced past the small intestine.

What is coprophagy?

Ingestion of feces, allowing additional absorption of vitamins and protein.

How does coprophagy work in rabbits?

Rabbits produce special pellets from the cecum, ingest them without mastication, and they ferment in the stomach.

How does rodent coprophagy differ from rabbit coprophagy?

Rodents produce pellets that are all the same and masticate them when reingested.

What is GI-tract plasticity?

The GI tract is a dynamic set of organs that can change in mass, linear dimensions, specific transporters, and enzymes.

What was the prairie-vole GI-plasticity experiment?

30–40 g rodents with a cecum that eat grass/leaves/stems were fed low- or high-fiber diets, kept at either 5°C or 25°C, and had gut size measured.

How do pythons demonstrate GI plasticity?

They can go weeks between meals and consume prey up to 70% of body mass. After feeding, midgut mass can double, sugar/amino-acid transporter synthesis can increase up to 20×, and metabolic rate up to 40×.

How do deer mice demonstrate GI plasticity?

During lactation, stomach, small-intestine, and liver mass increase proportionally to litter size.

How do pine warblers demonstrate GI plasticity?

They modify digestive enzymes based on diet type.

How do hibernating mammals demonstrate GI plasticity?

Intestinal mass peaks during the fattening season and may decline by more than 50% during torpor; marmots were given as an example.