VBMS 324- Final Rumen
Increased rumen turnover enhances microbial efficiency
-More turnover = bacteria spend more time actively dividing = increased microbial protein -More turnover= bacteria spend less time in maintenance phase (wasted energy) -But too much when rumen turnover can lead to diarrhea
VFA absorption in the rumen
-Most VFA are transported through the rumen wall (75%) but some are absorbed from omasum and abomasum (20%) while rest reach the small intestine -Rate of absorption is proportional to the length of VFA (butyrate> propionate> acetate)
Bacteria in the Rumen
-Most gram-negative, obligate or facultative anaerobes Bacterial locations in the rumen:: -Present as single cells or clumps -unattached, move with fluid in the rumen, ~50% of the total population -Attached to particulate matter (feed), move out rumen more slowly -Att tot the rumen epithelium
Balanced supply of CHO and N required for optimal protein synthesis:
-Need adequate amounts or ammonia, carbon skeletons, and energy for optimum bacterial protein synthesis to occur -Substrates must be available at the right times
Ammonia
-Non-proteon nitrogen (NPN) sources can be used to create ammonia -Nitrates/nitrites in plants -ammoniated straw, urea from feed (biuret) Other sources of N for NH3 -Urea fro saliva -From blood (across rumen wall) -Urease enzyme at rumen wall converts urea to ammonia maintaining conc gradient to urea to diffuse into rumen
Net energy production form CHO in ruminants: -Non-structural
-Non-structural CHO (starch, sugars) -Microbial breakdown to VFA (through glucose) -Subsequent absorption and utilization of VFA does not produce as much energy as straight digestion of starch in the intestines would (through amylase) -> slightly less efficient
Adverse GI events
Rumen acidosis- rumen drinking calves- fore stomachs become acidic -Leakage from esophogeal groove, failure to close, drinking too fast -Lactose fermented to lactic acid -Gas formation, rumen distention, fluid splashing -these calves don't gain weight as fast and slows the rumen and development intestinal bacteria overgrowth -Poor milk clot formation, excess milk enters duodenum, rapid proliferation of bacteria -Diarrhea
Protozoa feed on
bacteria, starch granules, protein in the diet and some sources of fat - some protozoa have enzymes to digest cellulose and hemicellulose (protozoa account for 25-30% of fibre digestion) Protozoa are more sensitive to rumen conditions than bacterial species therefore protozoa numbers and species are more variable
Pre-ruminant Intestines
all protein, degraded and AA absorbed, lactose hydrolyzed to glucose and galactose, limited starch digestion -Begin eating solid flood as animal gets older, but little nutritional benefit yet
Dissociated VFA's can pass through rumen _______________________
epithelium with cations (Na+) -CO2 from the blood diffuses into rumen epithelia cells -Conversion by carbonic anhydrase produces H+ for transport of dissociated VFAs Also produces bicarbonate to help buffer the rumen fluid
Feed intake (affecting pH)
higher feed intake results in lower rumen pH MORE substrate for fermentation (compared to a maintenance diet)
Cellulosome
multi-enzyme complex attached to the bacterial cell surface. allows the bacteria to adhere and degrade cellulose -Optimal growth at higher pH Longer life span
Starch
(alpha 1,4 glucose in linear strands) -No side chains - amylase -Side chains - amylopectin
Cellulose
(beta-1,4 glucose linkage) -Long linear strands arranged in a parallel
Hemicellulose
(beta1,4 xylise linkage, other monosaccharides used too) -BRANCHED side chains
Fiber: Neutral detergent fiber (NDF)
-More digestible -Composed of cellulose, hemicellulose and lignin -Digestible portion of finer -Related to amount of DM intake
CHO fermentatiomn-Other acids also produced but most rapidly used by other microbes
-Dissociated (ionized A) form vs. undissociated (non-ionized HA) form -ATP is produced for the microbe during fermentation -VFA skeletons can be used to produce AA of FA for the microbe
Rumen Fill
-Decrease while pregnant -Volume and weight of rumen contents help provide full rumen signals
How much colostrum
-2L shortly after birth Headstart- commercial colostrum replacer
Fungi/yeast
-5+ genera of fungi are present in rumen contents but #'s generally low -All are anaerobic and degradable cellulose, starch, xylan, along with other hemicelluloses and some protein -More important on high-fibre diets (up to 5-10% of microbial mass)
Rumen Development - Newborns
-Abomasum is by far the largest of 4 -Reticulorumen is very poorly developed -Normal microbial population is absent -Papilae are absent
Microbial Lipid metabolism
-Alcohol or sugar moieties are cleaved off, leaving only long-chain FA -LCFA complex with CA2+ (not soluble) pass to intestines -Hydrolysis breakdown of lipids in the rumen is performed primarily by bacteria- ester linkages b/w FA and glycerol are cleaved
Besides fermenting carbohydrates, bacteria can also:
-Degrade protein in feed and use the AA (as well as non-protein nitrogen) to create microbial protein, or for energy -Hydrolyze (break down) lipids and hydrogenate FA- why so much saturated fat in many ruminant products -Synthesize B vitamins (cobalt required for it b12)
Rumen turnover
-Amount of time required to replace the rumen contents with an equivalent amount of fluid or solid material -Fluid turnover -Inputs saliva, oral, water intake, water movement across rumen wall -Outputs: water moving across rumen wall to blood, passage to lower GI tract -Rate is most rapid on roughage diets and slowest on grain diets -Influenced mostly by salivation and water intake
VFA's are used to produced a large amount of a ruminant's maintenance energy. What would you expect form hindgut fermenters?
-Any soluble CHO have already been digested in the small intestine -Less substrate available for hindgut fermentation -VFAs less important for maintenance energy
Sequence of rumination events
-B4 primary contraction, reticulum contracts - extrac contraction not essential but helps ingest cover the cardia -Negative pressure created by inhalation (while airways are closed) -Cardia and distal esophageal sphincter relax, drawing cud into esophagus and it contracts cranially (reverse peristalsis) bud travels toward mouth -Tounge and jaw lowered, cud enters mouth -Tongue then raised to squeeze the liquid out (swallowed) -Solid cud remaining is chewed for 10-60 sec -Cud is swallowed before next regurgitation - only one cud at a time
Hydrogenation
-Bacteria add hydrogen to unsaturated FA, Therefore converting FA double bonds to single -Unsat FA are more toxic to bacteria than sat. FA -Not all unsaturated FA will be hydrogenated (~15% bypass) -Isomer changes-> cis to trans (more stable form, higher melting pt)
Bacterial Nitrogen Metabolism -Amino Acids
-Breakdown: aa from dietary protein can be deaminated to ammonia (NH3) and a carbon skeleton-> used to create VFAs -Incorporation: aa from dietary protein or dead bacteria in the rumen can be directly incorporated into bacterial protein -Synthesis: ammonia can be added to carbon skeletons (from VFAs and other metabolic products) to create new AA
Stimulatory inputs to gastric centres can originate from
-Buccal mechanoreceptors (eating and chewing) -Tension receptors -Epithelial (mucosal) receptors
Benefits of rumination
-Buccal receptor stimulation -increased salivation and rumen movement -more mixing of ingest -smaller particle size -surface area for microbes -greater chance of passing to omasum -nutrients will be unlocked quicker
Sources of protein absorbed in the ruminant intestine
-By-pass protein not fermented in the rumen -Microbial protein (bacteria and protozoa)
Colostrum
-Calves should receive 3-4 L asap -High immunoglobins -This passive transfer of immunity from mother to calf is essential to prevent early infectious disease: Scours pneumonia -naval infections -Rinch in vit A,D,E calcium and magnesium -Lactose is converted to glucose and galactose in intestines -Lactobacilli from the mammary gland help colonize the gut and prevent invasion by pathogenic organisms. E. coli, streptococci and clostrisial species will also begin colonization
Sources of Nitrogen in the Ruminant diet
-Dietary protein 60-80% -Nuclear protein -Non-protein nitrogen 5-60%
Clinical relevance of rumen pH
-Check a poor-producing dairy herd for sub-acute luminal acidosis -Stomach tube: risk of saliva contamination of the sample -Rumencentesis (lng needle through rumen wall) -> rise of infection -Neither method is 100% sensitive or specific, through rumenocentisis
Electrolyte Movement
-Chloride moves from rumen into blood stream -With electrical gradient -agains conc gradient -Sodium moves from rumen into blood stream -Against both electrical and chemical gradient (active transport) -Potassium move in both directions -no net difference water movement depends on osmolarity
Rumen Stratification
-Coarse feed material and low density particles form a "raft" floating on liquid density particles -founnd in grass eating ruminants "browser" ruminants don't have the same layers of stratification in rumen -As fermentation increase gas is removed from the forage and the density of particles will increase 'sinking' towards the omasal opening. Particles that are not dense will float on raft to be retained in the rumen for longer periods of time
Extrinsic motility
-Efferent branches of the vagal nerve (parasympathetic) required for rumen contraction -Multiple branches innervated different regions of reticulum and rumen -Responsible for both prim and sec contractions -Vagal nerve efferent activity will determine the frequency, amplitude and duration of rumen motility
Buffering capacity- Saliva (major functions in ruminants)
-Facilitates mastication -Modifies rumen pH -nutrients for microbes -antifrothing properties -enzyme content: pregastric esterase Salavary amylase absent in ruminants -Large parotid salivary glands in herbivores
Non-structural CHO
-Found in seeds, sometimes leaves/stems -Reseve souces of energy, mainly starch (grain) and simple sugars
Vagal nerve fires based on activity in the bilateral gastric centres of the medulla
-Gastric centre activation in the medulla is dependant on the balance of excitatory and inhibitory inputs from other receptors in the rumen and GI tract -Rumen receptors transmit signal to gastric centres via numerous afferent branches of the vagal nerve -Gastric centres stim and inhibit signals from the rumen
Why is pH lower with concentrate diets
-Grain - more readily fermentable, more rapid production of VFA's -Roughage - more saliva stimulated - more rumenation (saliva has bicarbonate buffer) Lactic acid isn't volatile because it stays as an acid
Giving colostrum to an older animal
-High energy -Systemic absorption of the antibodies -probably not useful because they are not producing pepsin and HCl, some ppl it if antibodies aren't digested could get localized immunity 7y
Inhibitory inputs to gastric centres can originate from
-High threshold tension receptors in reticulum and rumen cranial sac -Tension receptors in abomasum -Epithelial receptors in rumen -Pain (esp.abdominal) -Drugs
By-pass fat
-Increase energy density of feed but amount that can be fed is limited -Oilseeds (soybeans) -Animal fat (tallow, grease) -Other processed fat sources -Inert bypass fats-> generally insoluble, have less effect on rumen, bypass rumen Milk fat depression-> some diets can reduce the amount of fat in milk produced by ruminants
Abomasal secretion
-Is stimulated by suckling and the presence of milk in the abomasum - proteolytic enzymes (renin, not pepsinogen) and HCl secreted -Rennin with milk produces a hard clot (butter fat and curd) at 6.5 pH -Slowly degraded by lipase and esterase (slow rate of passage into duodenum, prevents intestinal overload -Albumin, globulins and lactose (the whey portion of milk) quickly enters the duodenum
Intrinsic Rumen Motility
-Low aptitude variations in smooth muscle tone due to intrinsic nerve network activity (enteric nervous system) -These changes in smooth muscle tone do not produce propulsive contractions -However, changes in smooth muscle in smooth muscle tone may excite sensory tension receptors that can induce extrinsic motility (rumen contractions
Fiber: Acid detergent Fiber (ADF)
-Least digestible plant portion --> mostly cellulose and lignin -Related to digestibility = increased ADF = decreased digestibility -Fiber is fermented slowly -Cows need a min amount of long hay to maintain rumen mat
Ruminant Fat Metabolism
-Lipids usually make up a low % of their diets -Fats vary in plants Lipids in plants can be: -Leaves (phospholipids in chloroplasts and membranes, galactolipids) -Waxy plant potions(esters) -Seeds (energy storage organs, is usually in the form of triglycerides)
Primary rumen contraction cycle
-Major mixing of ruminoreticulum HOW? -Double contraction of the reticulum -Contraction of dorsal rumen sac (cranial-> caudual) -Contraction of ventral rumen sac (cranial -> caudual) -20sec once per min -Loud How often depends on what animals doing -eating - most frequent, resting less frequent, ruminating mid
Structural CHO
-Make up cell wall, support -Made up of multiple monosaccharide units linked together includes Cellulose Hemicellulose Lignin Pectin
Rumen Gas Production
-Max gas production occur 2-4 hours after eating -produce up to 30-40L/h (cattle), 5L/h (sheep) -Eliminate bu eructation (secondary contractions) -major gases CO2 produced by decarboxylation during fermentation carbonic anhydrase CH4 reduction of CO2 and formic acid by methanogenic bacteria
Why does Eructation occur
-Microbes produce lots of gas - gas build-up occurs in dorsal rumen -Secondary contraction moves gas to the cardia region of the reticulum -fluid in reticulum is forced ventrally -Gas causes reflex opening of cardia and caudal esophagus -Animal inhales - negative pressure in thorax drawing gas into esophagus -Some gas exhaled directly, some enters lungs to be exhaled on next breath - gas can be absorbed into blood -Eructation can occur during primary contraction -If fluid/froth covering cardia is not moved ventrally - gas can't be expelled (frothy bloat)
Fermentation of CHO in the Rumen
-Microbial enzymes break down both structural and non-structural components of plants
Weaning to Adult
-Milk becomes less important -Reticular groove doesn't close consistently -Pepsinogen secreted in abomasums (no longer rennin) -Forestomach reaches adult proportions
Transitional phase (3->8 weeks)
-Milk still primary source of nutrition (consume 8-10% of body wt/d) but solid food more frequently eaten -Salavary glands increase in size and amount secreted -Proper rumen development requires dry feed: Solid feed will increase rumen weight and muscular wall development -Fermentation w/on rumen produces VFA's that increase the development of rumen papillae and omasal leaves
Rumen receptors: Tension receptors
-Monitor tension in the muscle wall Low/moderate distention will excite tension receptors and gastric centre, increase motility High tension causes inhibition of motility -Gastric centre switches from stim to inhib. signals with increase tension receptor firing --epithelial receptors reacting to extreme distension with inhibitory signals
Microbial lipid metabolism cont'd
-Odd # Carbon FA's can be produced by bacteria using propionyl CoA -Bacteria will incorporate FA into their structures (membranes) -not used for energy production (beta-oxidation requires O2) -Protozoa "hoard" unsaturated FA-released when protozoa are digested later in the GI tract -Remain unsaturated Ruminants don't need much lipase-> triglycerides digested for them by bacteria
Metabolic fate of VFAs in ruminant tissues
-Once absorbed from rumen epithelial cells, portal blood supply delivers VFAs to the liver B-hydroxybutyrate can be used by most tissues, and provides the initial carbon skeleton for FA in milk Propionate (and lactate) are removed from liver -Propionate is converted to oxaloacetate (4C), then to glucose -Only SCFA that can form glucose Acetate will form acetyl-CoA -Reacts with oxaloacetate to form citric acid -Also used in FA production
Why is it important to get colostrum into neonate quickly?
-after 2 days - lose ability to transport antibodies through the abomasum without digestion -Lose ability to transport antibodies through the abomasum without digestion -vital source of energy
Pre-ruminant Phase (24h-3weeks)
-Principle food is milk (~8% of body weight/day) Metabolism is glucose based and dependent on insulin -The rumen still has little function at this point but is beginning to grow -Active sucking stimulates increase secretion of saliva. The saliva contains pre gastric esterase which begins the hydrolysis of milk lipids
Rumen Undegradable Protein (RUP)
-aka Pass protein -Certain natural proteins -Processed protein -Specific by-pass AA Broken down by mammalian protease enzymes in abomasum/intestine
Processing (chopping, grinding) the diet will decrease pH (affect on pH)
-Reduces chewing, decreases saliva production (buffering) -Increases fermentation rate by increasing surface area
Rumination
-Regurgitating or chewing cud -High roughage diets - more frequent rumination (up to 10 hrs a day) -Mechanical stimulation of rumen epithelial receptors by long food particles -Cows appear content -GOOD HEALTH
The following rumen characteristics will promote overall microbial growth:
-Relative constant pH -Constant temperature -Constant rumen motility -Constant substrate (food) and water intake -Constant removal of waste of waste products -anaerobic environment
Types of protein in the ruminant diet- RDP
-Rumen degradable protein (RDP) -Only about half the dietary protein will be degraded by microbes -Bacteria most responsible for digesting dietary protein in the rumen -Only 10-40% of bacterial species will degrade protein -Ectracellular proteases degrade protein into peptide fragments-> absorbed into bacterial cell and degraded to AA -Protozoa can use dietary protein, but generally eat bacterial protein
Fermentation in the rumen continually produces acids -> so why isn't the pH even lower?
-Saliva (lots of HCO3 and phosphate buffers) -Carbonic anhydrase in rumen epithelial cells- donates H+ to acid anion, absorb acids into blood stream (out of rumen) HCO3-left in the rumen as a buffer -Can add NaHCO3
Lactic acid can be absorbed from the rumen, but much slower than VFA's
-Smaller quantities can be absorbed by the rumen -Very slow 10% of the absorption rate of VFA's Why? A strong acid K is much lower, more ionized in relatively neutral rumen pH
Other innervations to the fore stomachs
-Splanchnic motor nerves (symp) will inhibit motility. Sypm. input will modulate rumen contraction, but doesn't control it like vagal innervations does
Plant lipid is generally unsaturated (FA contain double bonds
-Stearic acid (10:0) -Oleic acid (18:1) -Linoleic (18:2) -Linolenic (18:3) -FA from plants are usually cis isomer
Orally administered drugs for ruminants (on rumen microbes)
-Tetracycline/ chlortetracycline/ oxytetracycline -neomycin -Tylosin -Sulfonamines
Secondary bacteria
-Use by products produced by primary bacteria for energy - lactate- using bacteria, hydrogen using bacteria
Rumen Osmotic Pressure
-Usually around 280 mOsm/L (hypotonic-> ECF ~300) -After feeding increase osmolarity of rumen due to increase fermentation
Secondary Rumen Contraction Cycle (eructation)
-Usually occurs after alternate primary cycle -Purpose is eructation (expel gas) -Not as loud as primary contraction -Sequence of contraction -Caudoventral ruminal blind sac (bottom) -Cranially -moving contraction of caudodorsal blind sac -Ventral sac -Rumen tips so that the gas rises over the cardia
In a weaned calf with functional rumen, what is absorbed through the rumen tissue?
-VFA's (acetate, propionate, butyrate) other SCFA (lactate, validate -electrolytes -water
What would you expect to see or hear
-Visual exam- see ripples at left paralumbar fossa -look for bloat Listening: ausculation -stethoscope over left paralumbar fossa (b/w ribs and hooks) -Loud primary cycle (rumbling -Fluid splashing or tinking - likely decrease in motility
Transitional phase (3->8 weeks) Cont'd
-grain especially useful -Rumen motility and attempts to regulate begin -Normal microbial flora begins to emerge-> est. of protozoal pop. requires repeated direct contact with other animals -Food and water contaminated by regulation, faces -Metabolism becomes based on VFA production, not glucose -less sensitive to insulin
Protozoa in the Rumen
-less than bacteria but almost equal in microbial mass -Numbers decrease with increase in rumen turnover -Two major categories of protozoa Holotrichs (cilia cover entire body) Oligotrichs (tufts of cilia at one end)
Bacteriophage (viruses)
-may help control bacterial populations (killing bacterial species)
Excess ammonia in rumen
-will be absorbed systemically and converted into urea in the liver (requires energy), excreted by the kindest or in the milk - risk of ammonia toxicity if too highly concentrated _ammonia is rapidly absorbed into the blood but ammonIUM (NH4) IS NOT
Factors effecting rumen pH
1. Diet (conc or roughage0 2. Feed intake 3. Time after feeding 4. processing (chopping, grinding) the diet will decrease pH
Why not just use by-pass protein in the feed and give NPN for bacteria?
?????
Fermentation produces VFA's from monosaccharides:
Acetate (2C) Propionate (3C) Butyrate (4C) Lactate is a short chain FA not VFA (3 carbon) -Lactate is normally produced in small quantities and used rapidly by secondary bacteria
Rate of absorption of VFA's increases as pH __________
Decreases -Non-ionized (undissociated) VFAs are absorbed more easily -Whether VFAs exist in their ionized or non-ionized form depends on their pK (4.6-4.8) and the pH of the rumen environment -HH eq can be used to determine the ratio of non-ionized to ionized VFA's at a pH
Reasons for decreased rumen motility: (rumen smooth muscle contraction requires stimulation via vagal nerve - gastric centres in the medulla)
Direct depression of gastric depression - certain drugs (tranquilizers..) -Acute phase proteins (fever, toxins, inflam) -Pain Decreased stimulation from peripheral receptors to gastric centre Increase inhibitory from peripheral receptors to gastric centre Failure of neuromuscular transmission - impulse transmission down vagal nerve -rumen /reticulum smooth muscle contraction -Increased sympathetic NS stimulation
Primary bacteria
Directly ferment the feed material eaten by the ruminant -Amylolytic bacteria: ferment starch (concentrates) -Optimal growth at acid pH (5.5-6.0) -short life span -Cellulolytic bacteria: ferment cellulose Produce extracellular enzymes to digest cellulose, but can also ferment starch as well
VFA are metabolized in the rumen ___________________
Epithelial cells: -Rate of metabolism increases with chain length (Ac<prop<but) Butyrate --> beta-hydroxybutyrate (a ketone body) Butyrate --> acetate Propionate -> lactate -> succinate
Non-fiber (concentrate)
Includes pectin, starch, sugar -Takes up little space in rumen as it can be completely digested -Fermentation much more rapid
Rumen receptors: Epithelial Receptors (2 types of stimulations)
Mechanical stimulation - light touch will cause rumination Sever distention causes inhibition of motility Chemical stimulation - Acid in rumen will result in inhibitory signals to gastric centre decreased motility -Acid in abomasum causes stim signals -increased rumen motility
Fiber
Slowly digested structural materia in plants (cellulose, hemicellulose, lignin NOT PECTIN) -Adds bulk and takes up space in rumen, requires increase chewing, forms rumen mat
Net energy production form CHO in ruminants:-Structural
Structural CHO Cellulose, hemicellulose, lignin) -Microbial breakdown to VFA (through glucose, xylose, and other monosaccharides) -Any VFAs absorbed and utilized by the animal are a bonus-> the ruminant would not gain energy if microbes not present
Overall animal production (meat and milk)is based on
VFA production, not proportion of VFA production
Pectin
alpha/beta 1,4 galacturonan linkage -Cements plant cell walls
Immunoglobulins are proteins,
and feeding colostrum to older animals will result in proteolysis in the stomach and intestines. How do antibodies in colostrum provide immunity to the newborn ruminant? Young calves protylotic digestion can be stopped in a newborn by not having HCl so pepsin not activated. Pepsin is not secreted -Anti-trypsin factor present in colostrum stops degradation by trypsin in intestines
Ionophores
class of oral antimicrobials that alter cell membrane permeability, selectively kill gram positive bacteria -Increases feed efficiency -Helps prevent acute lactic acidosis -Helps prevent frothy/grain bloat -Helps prevent ketosis -Prevention/treatment of coccidiosis
Gas removed from forage=
increased density -denser particles pass through rumen and reticulum faster
Rumen pH
normally 6-7 DEPENDANT on diet Roughage = 6.5-7.2 Concentrate = 4.9-6 (more concentrate - lower pH)
Time after feeding (affect on pH)
pH reaches its lowest pt. 3-4 hours after feeding -Starvation will result in an increase in pH b/c less substrate available for fermentation - so less VFA production -More frequent feeding - less fluctuation in pH
Lignin
phenol groups attached, almost undigestible (makes bark)
Suckling also stimulates closure of the
reticular groove, which are muscular folds of the reticulum. Milk passes straight to from the cardia to the omasal opening (bypassing the rumen) -Stimulates chemoreceptors in pharynx-> info to medulla via afferent pathway of cranial nerve IX -> vagal nerve efferent output closes the reticular groove and opens reticule omasal opening -Complex mechanism, seems to be affected by hunger: -if calf head butts udder and wags tail when suckling -> groove closure -if drinking because thirsty -> no tail wagging, no groove closure
Most protozoa are located in
the fibrous raft layer, liquid "soup" they are a good indicator of general rumen health -> if protozoa are happy rumen fermentation is stable and effective
