Lecture 6- Rumen physiology

Question 1

Why are ruminants important?

Answer 1

• Ruminants are extremely important for human food production • As much as we understand about the physiology of ruminants, many aspects are unknown or not fully understood • Control of intake in ruminants • Feed selection and preferences in voluntary feed intake • Nutrient partitioning • Etc. -lot of the microflora is unknown -nutrient partitioning= in pregnancy and lactation

Question 2

What is the classification of the ruminants we talk about?

Answer 2

• Ruminants are classified as Artiodactyla (Pecora)
• Important groups include deer, moose, antelope, giraffe, caribou, cow, sheep, goat

Note: camels, llama, alpaca etc. are grouped in the Tylopoda – they are not true ruminants. “Ruminants are earth’s dominant herbivores, due in part to the evolution within this group of a mechanism utilizing microorganisms to digest plant components not susceptible to attack by ruminant enzymes.” (Hungate 1975)

Question 3

What are the two suborders of ruminants?

Answer 3

1. Ruminantia: includes deer, moose, elk, reindeer, caribou, antelope, giraffe, musk, ox, bison, cow, sheep and goat 2. Tylopoda: camel, llama, alpaca, vicuna (do not have an omasum)

Question 4

How many ruminants are there in the world?

Answer 4

• Approximately 2.8 billion domesticated ruminants

Question 5

What defines all ruminants?

Answer 5

• Pre-gastric fermentation to produce volatile fatty acids • 4 compartment stomach • reticulum • rumen • omasum • abomasum -use pre gastric fermetation to produce volatile fatty acid= source of energy -4 compartment stomach= not 4 stomachs!!!

Question 6

What does the 4-compartment stomach look like?

Answer 6

-reticulum= catches rocks etc. -omasum= muscular= grinding food abomasum= true stomach -rumen= fermentation -rumination= rechew their food -the food passes through= then reguritate -rumen is the largest part by far

Question 7

What are the characteristics of the reticulum?

Answer 7

• Honeycomb lining • Formation of food bolus • Regurgitation processes • Collects hardware (nails, wire) -food bolus= for regurgitation -Most cranial compartment of the ruminant fore-stomach and serves as site that propels ingesta to flow into and out of the rumen thus regulating the passage of ingesta from the rumen to omasum. The reticulum also acts as a site to regulate water flow to rumen and during the process of regurgitation (flooding the cardia) -the more they chew the better -controls flow of ingesta -also water flow

Question 8

What are the characteristics of the rumen?

Answer 8

• Digestion and fermentation vat • Contains anaerobic microbes • Papillae lining • Absorption of VFA -dominant structure -covered in villi like structure -The rumen is a large, muscular sac that extends from diaphragm to pelvis which entirely fills the left abdominal cavity. It is subdivided into sacs with smooth muscle in walls. The function of the rumen is for soaking and fermentation of bulk fibrous food. Motility of the rumen means the contents are continually mixed – a continuous culture fermenter -it does move around, smooth muscle sacs -the bigs are unique to each individual cow.

Question 9

What is the reticular (oesophageal) groove?

Answer 9

-(relates to rumen)Most apparent in the pre-ruminant (calf) when suckling stimulates groove closure preventing milk from entering rumen and reticulum. This means milk enters the omasum and abomasum directly. With age the reflex is lost. -the reflex is closed and start eating grass= the bigs will start forming in their stomach -the development of their rumen is crucial

Question 10

What are the characteristics of the omasum?

Answer 10

-grinds things • Laminae lining • Reduces particle size • Absorption of water • Absorption of VFA - The omsaum is filled with muscular laminae that are covered by mucus membrane studded with short, blunt papillae. The site of digestion provides for the continued fermentation of digesta and absorption of VFA. -The organ also regulates the transfer of digesta from the reticulo-rumen and abomasum. -Usually the organ is packed tightly with particles and it is thought that particle size reduction occurs in the organ. -full of muscle, the bugs keep on digesting while going through

Question 11

What are the characteristics of the abomasum?

Answer 11

• True gastric stomach • Proteolytic enzymes • Gastric digestion • Decreased pH from 6 to 2.5 • Denatures proteins • Kills bacteria and pathogens • Dissolves minerals (e.g., Ca3(PO4)2) -pH changes through the rumen= depends on diet etc. -important to kill the bacteria so they don’t get to the small intestine -The true stomach. It is the first glandular portion of ruminant digestive system. The terminal portion of the abomasum is known as the pyloric region and is bounded by a sphincter. The sphincter controls the flow from the abomasum to the small intestine. The flow from the abomasum is regulated by a series of peristaltic contractions. The flow of digesta from the abomasum is down regulated by the fill of the first segment of the small intestine – the duodenum.

Question 12

What are the 4 phases of rumination?

Answer 12

-The reflex is initiated by the mechanical stimulation of receptors in the mucosa of the reticulum and rumen in the areas of the cardia. It is a four stage process: 1. Regurgitation, 2. Remastication, 3. Reinsalivation, 4. Redeglutition.

Question 13

What is phase 1. regurgitation?

Answer 13

-This phase is preceded by the contraction of the reticulum. The cardiac sphincter at the junction of oesophagus and the stomach relaxes as the bolus of food reaches it. Parasympathetic stimulation leads to sphincter relaxation and feedback to other parts of the digestive tract. There is an increase in activity (digestive tract wall), followed immediately by an inspiratory movement that leads to glottis closure. -The negative pressure produced in the thorax by the activity of the digestive tract allows migration of digesta to the oesophagus causing the thoracic oesophagus and cardia to dilate. -The pressure in the oesophagus is lower than the rumen and this, coupled with reverse peristalsis causes a quantity of material (semi-fluid ingesta) to pass through the cardia to the oesophagus and therefore to the mouth. -reticulum pushing the food back up

Question 14

What is phase 2. remastication?

Answer 14

-This process is the re-chewing of the bolus regurgitated into the mouth. It is a more leisurely process compared to the initial chewing of the feed. -This means the rate of chewing is reduced by approximately 30% in cattle offered high roughage diets. -Rumination time varies considerably between animal type and also diet type. However the average rumination time is about 8 hours/day. During rumination there is, on average, one cycle per minute.

Question 15

What is phase 3. Reinsalivation?

Answer 15

Reinsalivation mixes the bolus with more saliva. This increases: (1) the amount of bicarbonate added to the digesta (increased supply of buffering agent), (2) increases the pH of the digesta and mixes recycled urea with the feed. Re-insalivation is also necessary to assist swallowing of the re-chewed digesta.

Question 16

What is phase 4. redeglutition?

Answer 16

This is the process of re-swallowing the bolus after the feed particles have been subdivided further and reduced to a size that allows migration through the reticulo-rumen omasal orifice or to be transported via the omasal groove to the abomasum. The latter process is poorly understood.

Question 17

What is the microbiology of the rumen?

Answer 17

-The rumen is the world’s largest commercial fermentation. -It is estimated that the rumen is a 100 billion litre fermenter in domesticated livestock. • Relative stable population for a given feed (substrate) • Microorganisms adapted to rumen environment • Mostly obligate anaerobes • Bacteria - 1010 to 1011 cells/g • Protozoa - 105 to 106 cells/g • Fungi - 103 to 105 zoospores/ml -if go from grass to wheat= change in rumen microflora -take bugs from one and put into another animal= it reverts to the old microflora quickly

Question 18

What are the 4 groups of bacteria associated with the rumen?

Answer 18

1.Free-floating in the liquid phase 2.Associated with feed particles 3. Associated with rumen epithelium 4. Other

Question 19

What are the Free-floating in the liquid phase bacteria in the rumen?

Answer 19

• Maybe up to 50% of bacteria in rumen are free floating • Probably daughter cells of attached bacteria • Feed on solubles released by attached cells

Question 20

What are the Associated with feed particles bacteria in the rumen?

Answer 20

• Loosely associated with feed particles • Firmly adhered to feed particles • Up to 75% of bacteria associated with feed particles. Do most of the initial digestion of feed particles

Question 21

What are the Associated with rumen epithelium bacteria in the rumen?

Answer 21

• Similarities and differences from bacteria in the • rumen fluid • Suggested functions • Scavenging O2, tissue recycling, digest urea

Question 22

What are the other bacteria in the rumen?

Answer 22

• Attached to surface of protozoa and fungi • Engulfed in protozoa

Question 23

What do the bacteria associated with Feed Particles Groups 2 and 3 do?

Answer 23

• 75% of bacterial population in rumen • 90% of endoglucanase and xylanase activity • 70% of amylase activity • 75% or protease activity

Question 24

What are the phases of the bacterial adhesion to plant tissues?

Answer 24

1. Transport of bacteria to fibrous substrate Low numbers of free bacteria & poor mixing
2. Initial nonspecific adhesion Electrostatic, hydrophobic, ionic On cut or macerated surfaces
3. Specific adhesion to digestible tissue Ligands or adhesions on bacterial cell surface
4. Proliferation of attached bacteria Allows for colonization of available surfaces

Question 25

What are the carbohydrate epitopes of bacterial glycolcalyx?

Answer 25

• Slime layer surrounding bacteria composed of • glycoproteins • Proteins and carbohydrates involved in adhesion

Question 26

What are the cellulose-binding domains of cellulolytic enzymes?

Answer 26

• Cellulase has two functional domains • Catalyticdomain-hydrolysis of glycosidic bonds • Binding domain - binds enzyme to cellulose

Question 27

What happens if attachment is prevented or reduced?

Answer 27

-digestion of cellulose greatly reduced • Brings enzymes and substrate together in a poorly mixed system • Protects enzymes from proteases in the rumen • Allows bacteria to colonize on the digestible surface of feed particles • Retention in the rumen to prolong digestion • Reduces predatory activity of protozoa

Question 28

What are the Nutrient Requirements of Cellulose Digesters?

Answer 28

• Carbohydrates (source of energy) • Branched chain volatile fatty acids • Isobutyric, isovaleric, 2-methylbutyric • Needed for: • Synthesis of branched chain amino acids • Synthesis of branched chain fatty acids (phospholipids) • CO2 • Minerals (PO4, Mg, Ca, K, Na, probably other trace minerals) • Nitrogen • Mostly NH3 rather than amino acids • Biotin is stimulatory in pure cultures

Question 29

What is the effect of pH on cellulose digestion?

Answer 29

Low pH (6.0)decreased rate of cellulose digestion, but had little effect on subsequent ability to digest cellulose.

Question 30

What is the effect of sugar on cellulose digestion?

Answer 30

Added sugar was a source of readily available energy from 0 to 24 h. Subsequent drop in pH after 24 h limited the rate of cellulose digestion after 36 h.

Question 31

How is pH regulated in the rumen?

Answer 31

• Dairy cow can produce up to 160 moles fermentation acids/d • Buffers secreted in saliva • Phosphate pK of 6.5 • BicarbonatepKof6.4 • Below 5.7 bicarbonate & phosphate not effective buffers • At low pH VFA become most effective buffer • Feeding effective fibre (forage) results in less acidic rumen -Increased saliva flow – but osmotic pressures in rumen maintained close to that of blood and interstitial fluids so bicarbonate concentrations in the rumen do not vary much -Only undissociated forms of VFA readily absorbed so rumen has to be acidic for an increase in VFA absorption -More likely increased saliva flow increases fluid dilution rate • As high as 20% per h when forages fed • Compared with 5% per h when cattle fed grain Increased amounts of VFA washed out of rumen

Question 32

What are some of the types of bacteria?

Answer 32

-some utilize starch, some lactic acid, some sugar, some pectin and some hemicellulose

Question 33

What are the acetogenic bacteria?

Answer 33

• Reduce CO2 at expense of hydrogen • 2 CO2 → CH3COOH + 2 H2O • Bacteria present in rumen and hind gut of several species • Do not compete with methanogens for hydrogen • H2 threshold 100 times greater • Only of significance if methanogens inhibited • If active would conserve energy loss from the fermentation • Fact they are present in the rumen indicates they might • use other substrates

Question 34

What are the rumen protoza?

Answer 34

• Majority are ciliates • Low numbers of flagellates • Obligate anaerobes • 20 to 200 um length • Very motile • Not attached to feed particles • Calves isolated from birth do not become faunated. -Counts up to 10 to the 6 cells/g 50% of microbial mass 

Question 35

What is the role of protoza in the rumen?

Answer 35

• Digestion and fermentation • Carbohydrates and proteins • Ingest bacteria and feed particles • More of a digestive process. • Engulf feed particles and digest CHOH, proteins and fats. • Produce volatile fatty acids, CO2, H2 & NH3 • Make a type of starch (amylopectin) that is digested by the animal. -ruminants get protein from the protozoa

Question 36

What are the contributions of protozoa to the animal?

Answer 36

• Observations -Numbers in increase when grain is added to forage diets – up to 40 to 60% concentrate -Low rumen pH when high-grain diets are fed results in loss of protozoa (Numbers decline below pH 5.6) -Only a slight decrease in digestion when defaunated No change in growth of the host animal • Large mass • Mass of protozoa might equal mass of bacteria • Protein supply for animal • Number of bacteria declines in faunated animals • Some question how much of the protozoa mass leaves the rumen • Estimates range from 50 to 85% lyses in the rumen – Very sensitive to O2 and oxidation-reduction potential • Digestive enzymes probably remain active in the rumen • Provide nutrients for bacteria

Question 37

What are the rumen fungi?

Answer 37

• Initially thought to be a flagellated protozoa. Later showed to contain chitin – representative of fungi • Five genera have been found in the rumen: • Neocallimastix • Piromyces • Caecomyces • Orpinomyces • Anaeromyces • Anaerobic flagellated organisms • Life cycle includes motile zoospores and non motile vegetative form • Zoospores attach to feed particles followed by encystment and germination • Counts range from 1.5X103 to 1.5x106 per g rumen contents

Question 38

What is the role of the rumen fungi?

Answer 38

• Fungi can degrade cellulose, starch, xylan, hemicellulose & pectin • Some evidence of esterases that free CHOH from lignin • Ferments cellobiose, maltose, sucrose, glucose, fructose & xylose • Role of the fungi not clearly established in mixed cultures with • bacteria. Bacteria seem to inhibit the fungi.

Question 39

What is the energy supply to ruminants like?

Answer 39

-Contribution of the microbes to the symbiotic relationship: -VFA 70% -Microbial cells 10% -Digestible unfermented feed 20% -Concentration of VFA in the rumen = 50 to 125 uM/ml

Question 40

What is the amino acid supply to ruminants like?

Answer 40

-Protein in microbial mass 65% -Undegraded feed proteins 30% Recycled endogenous proteins 5% -Amino acid balance of microbial mass is superior to that from undegraded feed proteins when corn-based diets are fed.

Question 41

What do microbes provide to the ruminant? EXAM TIP!

Answer 41

• Microbes provide to the ruminant • A mechanism to digest cellulose and hemicellulose (mammals do not possess cellulase or hemicellulase) • Supply of high quality protein (microbial origin) • Provision of B vitamins • Detoxification of potentially toxic compounds -Mutualism: an important concept in rumen microbiology

Question 42

What is mutualism?

Answer 42

-The ruminant is a mutuality where the microbe provides nutrients by the digestion of substances difficult/impossible for the animal to degrade. The microbial community also provides vitamins and co-factors. In return the animal provides the habitat. -The arrangement is not commensal (i.e. the animal provides the habitat only) nor is it directly predatory – that is the animals prey directly on microbes – but there is an indirect “preying” of the animal on the rumen microflora.

Question 43

What is the microbial supply of protein to ruminants?

Answer 43

• Provision of high quality protein • 50-80% of absorbed N is derived from the rumen microbial ecosystem • Improved microbial efficiency will provide more microbial protein (manipulation of diet – see later lectures on protein systems) • can provide over 3 kg of microbial protein per day • High biological value protein source • Amino acid pattern is very similar to that required by the ruminant animal

Question 44

What else do microbes provide for the ruminants?

Answer 44

• Provision of B vitamins – see later in vitamin lectures • The supply meets the ruminant’s requirements under most conditions – especially vitamin B12 and niacin • Detoxification of toxic compounds, for instance the detoxification of mimosine. • Mimosine in Leucaena can lead to poor growth, reproduction and fleece loss (Australia) • However microbes that degrade mimosine are endemic to regions in central America. Leucaena is an option in those agricultural systems as a high quality protein forage.

Question 45

What is the bacterial digestion of feed protein?

Answer 45

• Microbes utilise N, amino acids and peptides for their protein synthesis • Microbes convert dietary proteins into their own protein. • The concept of biological value does not work with ruminants. • For instance some amino acid conversion occurs so dietary amino acids does not equal amino acids leaving the rumen and the dietary protein is supplying the microbial community not the animal per se directly.

Question 46

What is the bacterial digestion of lipid?

Answer 46

• Microbial lipases act on triglycerides • Biohydrogenation is a process that occurs extensively in the rumen. • Biohydrogenation is the addition of H+ across a double bond that leads to the saturation of already existing unsaturated fatty acids.

Question 47

What is lipolysis?

Answer 47

-

Question 48

What is biohydrogenation?

Answer 48

• Reduction of double bonds • Result: fatty acids that are more saturated with hydrogen -The addition of hydrogen to a compound, especially to solidify an unsaturated fat or fatty acid.

Question 49

What are the factors that reduce microbial growth?

Answer 49

• Rapid, dramatic ration changes • takes about 3 weeks for the microbial community to completely stabilise • Feed restricted amounts of diet • Feed containing elevated levels of unsaturated fat • Bacteria do not use fat for energy • Inhibit fibre digestion (not by coating the fibre) and microbial growth • Feed containing high levels of non-structural carbohydrate that when fermented leads to a lower rumen pH (rumen acidosis) • Bout feeding • Highly processed barley or wheat • To prevent acidosis, there must be a mechanism to balance lactate producing bacteria and lactate utilising bacteria

Question 50

What are the factors that maximise microbial growth?

Answer 50

• Maximise dry matter intake • Balanced (synchronise) carbohydrate and N supply in the diet • Bacteria need both energy and N for amino acid synthesis • Gradual change when altering a ration – ‘weaning animals on or off a feed’ • Maintain rumen pH above pH 6.3 • Maintain an ad libitum feeding regime