Ruminant GIT 2.

Question 1

How do ruminants digest food?

Answer 1

-Ruminants eat a voluminous diet that is rich in fibre and low in digestibility (cellulose, lignin).
-This plant cell material cannot be broken down effectively by animals themselves (needs microbial enzymes for fermentation).
-There is a large VAT (e.g., rumen to allow for fermentation and mechanical breakdown of food, which is a lengthy process).
-Regurgitate undigested food for further digestion RUMINATION.
-Ruminants are forestomach fermenters.

Question 2

Rumen the ‘microbrewery’?

Answer 2

-Equivalent to a microbrewery:
1.) Large active store VAT.
2.) Full of microorganisms.
3.) Storage, mixing, mechanical breakdown, and fermentation.
4.) Passed to abomasum for enzymatic digestion.

Question 3

Day in the life of a cow?

Answer 3

-Consume up to 20 meals a day.
-Lie resting for 12-24 hours a day.
-Spends 8-10 hours ruminating.
-Produces 100-150 litres of saliva per day.
-Does 30, 50,000 chewing jaw movements a day.

Question 4

What does the rumen need?

Answer 4

-Regular addition of new (chewed) food.
-Stable intraruminal conditions:
1.) Temperature (above rectal temperature).
2.) Osmotic pressure (slightly hypotonic).
3.) pH (6.5-7.0).
4.) Stable microbial population.
-Mixing of food material in the rumen.
-Removal of end products of fermentation.
-Onward propulsion of foodstuffs.

Question 5

Salivation = important for bicarbonate production?

Answer 5

-Cows produce up to 100-150 litres of saliva/day.
-Saliva contains:
1.) Bicarbonate: pH of 8 buffers rumen contents.
2.) Phosphate.
3.) Urea.
-Basal level of saliva secretion always occurs.
-Stimulated further by:
1.) Chewing of food.
2.) Tension receptors in the reticulum.

Question 6

Fermentation-Key process to ruminant digestion?

Answer 6

Who does that?
-Rumen microbes:
1.) Anaerobic bacteria.
2.) Anaerobic protozoa.
3.) Anaerobic fungi.
-Optimum pH 6.5-7.0 and requires anaerobic conditions.
-Provides energy and substrates for:
1.) Microbe population maintenance and growth.
2.) Cow maintenance and growth.

Question 7

Rumen microbes?

Answer 7

-Anaerobic bacteria:
1.) Cellulolytic enzymes.
2.) Breakdown cellulose and hemicellulose–> starch and sugar.
-Protozoa:
1.)Ferment mainly starch and sugar.
-Anaerobic fungi:
1.) Digestion of plant cell walls.

Question 8

Products of fermentation by microbes?

Answer 8

-Volatile fatty acids (from carbohydrates):
1.) Propionate.
2.) Butyrate.
3.) Acetate.
-Amino acids and ammonia (from proteins).

Question 9

Rumen undergradable protein (RUDP)?

Answer 9

Proteins in the diet that are not digestible by rumen microbes (e.g., fishmeal).
RUDP passes straight to the abomasum for enzymatic digestion.

Question 10

What are the end products of fermentation?

Answer 10

-Volatile fatty acids (VFA):
1.) Acetate.
2.) Butyrate.
3.) Propionate.
-Ammonia.
-Microbial cells: an important protein source for animals.
-Gases (up to 30 litres/hour):
1.) Methane (40%).
2.) Carbon dioxide (40%).

Question 11

What happens to the end products of fermentation?

Answer 11

-VFA:
1.) Absorbed through the forestomach wall.
2.) Taken to the liver for further metabolism.
-Ammonia:
1.) Made into microbial protein.
-Microbial cells:
1.) Digested in the abomasum and small intestine.
-Gases:
1.) Eructated.

Question 12

Rumen content layers?

Answer 12

-Gas cap:
1.) Methane.
2.) Carbon dioxide.
-Fibrous mat:
1.) The majority of long fibres.
2.) High density of microbe-digesting food.
3.) Recently eaten food added to this layer.
-Liquid layer:
1.) Fine particles under 2mm.
2.) Transport material around rumen.

Question 13

Rumen contractions?

Answer 13

-Coordinated a series of contractions.
-Four main functions:
1.) Mixing food material.
2.) Move food material.
3.) Erucatation.
4.) Rumination.
-Main innervation by vagus nerve: vagal indigestion.
-Originate from the gastric centre in the medulla oblongata.

Question 14

Primary contractions- for mixing?

Answer 14

-Biphasic contractions of reticulum:
1.) Reticulum contracts and ejects food over the ruminoreticular fold.
-The ruminoreticular fold contracts and shortens (at the peak of 2nd contraction, the reticuloomasal orifice briefly dilates to allow emptying into the omasal canal).
-Contraction of the dorsal sac of the rumen.
-Contraction of the caudal bind sacs of the rumen.
-Contractions of the ventral sac of the rumen.
-One cycle every 40 seconds.
-Process takes approximately 20 seconds.
-Auscultate in the left sublumbar fossa.
WHY?

Question 15

Secondary contractions- crnail movement gas cap?

Answer 15

-Not always present:
1.) usually follows the primary contraction cycle, but can happen independently.
-Necessary to expel gas from the rumen.
-Cardia needs to be covered by a free gas gap.

Question 16

Secondary contractions- B cycles?

Answer 16

-Does not start with reticular contractions:
1.) Contraction of the caudal ventral blind sac.
2.) Contraction of the caudal dorsal blind sac.
3.) Contraction of the dorsal sac of the rumen.
4.) Contraction of ventral sac of the rumen.

Question 17

Coordination of rumen cycles?

Answer 17

-One primary contraction cycle every 40 seconds:
1.) Auscultate the left sublumbar fossa.
-One secondary contraction for every two/three primary contractions:
1.) Auscultate over the oesophagus.
-Frequency of rumen contractions may alter:
1.) Increased when eating.
2.) Reduced when resting.
3.) The force and frequency are modified reflexively by mechanoreceptors in all of the reticulum (‘reflexogenic zone’).

Question 18

Rumination?

Answer 18

-The process of regurgitation, rechewing, reinsalivation, and reswallowing:
1.) Breaks down food material into smaller particles = increased surface area for microbial fermentation.
2.) Releases intracellular products of ingesta for fermentation.
3.) Soaks the digesta in saliva (urea and buffers).
-Sign of health and general well-being.
-Allows better digestion by rumen microbes.
-Commences at 2-3 weeks of age if given access to solid food.
-Always superimposed on primary contractions; therefore, frequency is roughly 1/minute.
-During rumination, greater fermentation leads to more gas production; therefore, frequency of secondary contractions and number of eructations increase.
-Stimulated by:
1.) Small amounts of circulating VFA’s (chemoreceptors in CNS, reminoreticulum and liver).
2.) Abrasion of reticulorumen epithelial receptors (mechanoreceptors).
3.) Long fibre (>25mm).
-Duration is dependent on diet:
1.) High roughage diet: 8-10 hours a day.
2.) High-concentration diet: <2 hours a day.

Question 19

Control of rumination?

Answer 19

-Central neural mechanisms:
1.) Higher CNS control centres in the hypothalamus.
2.) Chemoreceptors sensitive to circulating VFA’s.
-Peripheral neural mechanisms:
1.) Enteroreceptors:
2.) Mechanoreceptors: sensitive to tension and stretch of reticulorumen (e.g., coarse, unchewed fibre).
3.) Chemoreceptors: in rumenoreticular epithelium and liver are sensitive to VFA’s.

Question 20

What inhibits rumination?

Answer 20

-Pain and fear.
-Activity of the hypothalamic feeding centre.
-Deep sleep.

Question 21

Eructation?

Answer 21

-Relex event involving the oesophagus and pharynx.
-One cow produces up to 30 litres/hour of methane.
-Most is removed by eructation (refer to fermentation animation on earlier slide).
-Rumen wall is permable to gas:
1.) 25% is absorbed into the hepatic portal blood.
-Inhibited by the cardia being flooded (e.g., lateral or dorsal recumbency).
-Usually, the reticulum is full of liquid ingesta covering the cardia.
-Before erucatation can occur, the carida must be cleared of liquids by a contraction of the ruminoreticular fold.
-Majority of erucatations occur during primary contractions.
-Only 30# of eructations occur at the end of the secondary contractions.

Question 22

Clinical examples– Bloat (rumen tympany)?

Answer 22

-What do you think happens if there is an obstruction?

-This is known as Rumen tympany.
-There are two types:
1.) Primary or Frothy bloar due to a lush leguminous pasture.
2.) Secondary or Free gas bloat due to an obstruction.
-Do you think recumbency of a cow affects gas?
1.) Lateral or dorsal recumbency actually inhibits eructation.