Ruminant Digestive Physiology

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Monogastric: Simple digestive system and purely enzymatic digestion

Avian digestion:

Mouth/Beak: gathers and breaks down feed

Oesophagus: tube from mouth to stomach

Crop: feed storage and moistening

Proventriculus: glandular stomach enzymatic

Gizzard: muscular stomach; mech breakdown

Small intestine: Enzymatic digestion & absorption, Digestion of proteins, carbohydrates, and fats, Absorption of the end products of digestion

Caeca: Non-functioning in monogastrics, limited bacteria - horses, rabbits

Large Intestine: bacterial activity, water absorption, waste storage

Cloaca: common chamber for GI and urinary tracts

Vent: common exit GI & urinary tracts

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Ruminants:

4 compartmented stomach

Rumination: Regurgitation, rechewing and reswallowing of ingested food

Cud: mass of regurgitated ingesta; bolus

Process of rumination:

Regurgitate bolus from rumen

Re-chew and re-insalivate

Re-swallow

Repeat with another bolus

Lack salivary amylase (breaks down carbohydrates), present further through digestive tract

Reticulum, Rumen, Omasum, Abomasum

Reticulum: Like a sieve that sifts out dangerous and tough material. Filtered material stays in reticulum. Houses microorganisms. Leads to omasum.

Rumen:Largest compartment with 80% capacity, storage area for feed, millions of bacteria and protozoa that break down feed. Anaerobic, 39 degrees celcius, saturated with gases, papillae form rumen mat for microbes to reside. Peristaltic movement. Rumen microorganisms digest roughages to make VFA's (Volatile Fatty Acids), synthesise microbial protein, synthesise vitamins K and B complex.

Omasum: Very muscular, squeezes out and absorbs water. Full of open tissue (book-like)

Abomasum: Digestive juices, cause chemical changes that break down proteins, carbohydrates and fats into simpler substances to pass into small intestine for further digestion and absorption. True stomach that secretes enzyme pepsin and acid (hydrochloric)

Mouth: Contains dental pad, teeth, tongue & saliva. Saliva contains no salivary amylase.

Oesophagus: Tube from mouth to stomach, Tube from stomach to mouth

Small intestine: Enzymatic digestion and absorption. Digests protens, carbohydrates and fats. Absorb end products of digestion (3 sections: duodenum, jejunum, ileum)

Caecum: Some microbial fermentation

Large intestine: water absorption and waste storage

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Impact of feed on rumen development

4 weeks: Grain, milk and hay develops rumen faster. Milk and hay only causes less rumen microbe development and less papillae.

6 weeks: Milk only: Less development, milk and grain: Develop much faster. Diets for rumen development: Milk only < Milk + Hay < Milk + Grain.

Faster rumen development allows earlier weaning

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Krebb's Cycle

All you need to know:

When animals consume carbohydrates, they get broken down into hexose. Hexose broken down by nicotinade adenine denucleotide into VFAs. Different feeds synthesise fatty acids.

More grass -> more acetate

More grain -> more propionate

Methane (CH₄ given off)