Digestion in ruminants stomach
Features of digestion in ruminants
Gastro intestinal tract has colonies of microbes. As the animal grows the type of microbes gets modified according to the type of diet. Host animal and its populations of gut microbes interact. There is a complex interaction between the host animal and microbial population. Host animal does not produce enzymes degrading cellulose and other plant polymers, hence depends on metabolic activities of gut microbes to utilize the fibrous food. Microbial cellulose digestion is a slow process hence they are retained for longer period in the gut.
- Value of microbial products are more to the host (VFA/ Vitamin B Complex)
- They are well absorbed in rumen and lower stomach
- Ammonia and non protein nitrogen ,metabolized by microbes to synthesize good quality microbial protein which is later digested by the host.
- Large fibrous particles are selectively retained in the reticulo-omasal orifice for mechanical breakdown.
- Large quantity of gases produced by metabolism is readily expelled by eructation.
- Large output of saliva provides high buffering action against VFAs and also media for microbial growth.
- Toxic substances are detoxified during fermentation before getting into the small intestine.
Mechanical factor of digestion in ruminants
| Mastication | Grinding of the food particles |
| Deglutition | Swallowing of patially graind food materials (Cud) from the mouth into oesophagus |
| Rumination | Chewing of the cud. This occurs in four phases |
| Regurgitation | Reentry of cud, the liquid portion from the reticulum in to the mouth |
| Re-mastication | Regrinding of the cud |
| Reinsalivation | Additional salivary secretion to the bolus |
| Redeglutition | Re-swallowing of the bolus from the mouth into oesophagus |
| Eructation | Elimination of CO2 and CH4 from GI tract |
Rumination
- This consists of four processes
- Regurgitation
- Re-mastication
- Reinsalivation
- Redeglutition
- Rumination is a reflex initiated by mechanical stimulation of mucosal receptors of reticulum, ruminireticular fold, rumen and cardia.
- Particles of the feed influences the time on rumination.
- Feeding of hay diet requires eight hours of rumination. Feeding well chapped smaller pieces of grass reduces time of rumination.
- Rumination starts with third contraction of reticulum viz regurgitation contraction which aids in clearing the cardia for opening.
- Regurgitated bolus is primarily of liquid ingesta.
- From reticulum it is pushed reflexly to opened cardio oesophageal sphincter.
- Lower intra oesophageal pressure at this point causes the pressure gradient to flood the ingesta from the stomach to cardia.
- Forceful inspiration with closed glottis causes decrease in intrapleural and intra oesophageal pressure.
- The presuure gradient is purely achieved by forceful inspiratory effort mediated by the contraction of costal muscles and not by ruminal/ reticular contraction.
- Reverse peristalsis moves the regurgitated bolus from esophagus to mouth. In the mouth, the liquid ingesta from the bolus is squeezed and swallowed. This is followed by reinsalivation and remastication.
- Vagus provides the afferent fibres and the rumination center is located in the brain stem.
- Efferent fibres supply to salivary gland, esophagus, reticulum, muscles for inspiration, mastication and deglutition.
Nervous control of Rumination
- Rumination
- It is the process of bringing back the cud from the rumen and reticulum to the mouth for further chewing.
- Regurgitation
- The cud that returns to the mouth is mainly the liquid from the rumino reticulam.
- The regurgitated cud consists of small particulate matter highly mixed with liquid and in advanced stage of fermentation.
- Freshly eaten forages whose particle size is too great to be suspended in the rumen fluid for extensive maceration and are not regurgitated.
- The glottis is closed by the elevated soft palate and inspiratory effort with tongue causes a drop in intra-thoracic and intra-oesophageal pressure.
- The cardia and caudal oesophageal sphincter get open, simultaneously extra-reticular contractions force the cud from the retuculum into the oesophagus due to negative intra-thoracic pressure.
- An antiperistaltic wave of oesophagus carries the cud to mouth.
- Remastication
- In the mouth, the liquid portion of the cud is squeezed and swallowed. The remaining solid mass is chewed with slow, regular chewing movements for about 40-seconds.
- Reinsalivation
- During the process of remastication saliva is added from parotid gland followed by reswallowing
- Redeglutition
- It is the act of reswallowing of the cud
- Time spent in rumination varies in different animals and with different rations.
- Average daily duration for rumination in cattle is 10 hours on hay diet.
- The proportion of grain and roughage in ration influences rumination time.
- With low roughage diets or finely ground roughage,total rumination time may be reduced to 3 hours/ day.
- Peak rumination occurs during afternoon and in the middle of the night.
- Nervous control of rumination
- Rumination is a reflex act, but it can also be influenced by voluntary control.
- The receptors for rumination are in the reticular wall, cranial pillars of rumen and rumino-reticular fold.
- Vagus provides afferent nerve fibres to the rumination centre in the medulla.
- The efferent nerves are the motor nerves controlling muscles of larynx, oesophagus, and reticulum.
Eructation
Eructation is the expulsion of fermentation gases like CO2 and methane that has accumulated in the rumen.
- Receptors for eructation reflex are the tension receptors located in the reticulum, cardia, and cranial rumen sac, which are stimulated by accumulation of gas.
- Vagus provides both afferent and efferent fibres. Eructation centre is present in medulla.
- Volume of gas produced in rumen of a dairy cow is ½ to 1 litre/minute. The gas layer is moved cranially by the secondary contraction of the dorsal sac.
- The cardia and lower oesophageal sphincter open, and the gas enter into the relaxed oesophagus. By an antiperistaltic wave in the oesophagus and elevation of soft palate the gas is expelled through the mouth.
- Free gas found at the top of the ingesta in the dorsal rumen sac move cranially and ventrally to the cardia. Cardia remains closed by contact with watery ruminal content. Cardia gets free of ingesta during the contractions of dorsal sac, cranial pillar and caudal pillar.
- Accumulation of gas in the dorsal sac is the primary stimulus of eructation. Increase in the pressure in the dorsal sac of the rumen increases the eructation frequency and amount of gas expelled.
- Eructation occurs once in two ruminoreticular contractions. Inhibition of eructation isobserved during blokage of ruminoreticular contraction. Block of eructation leads to bloating of the rumen, called as TYMPANY which can also happen when gas production is higher than the elimination.
- Rumen distension decreases the lung volume and alters breathing pattern. Mechanical activity of the diaphragm is inhibited. Oils and non absorbable surfactants are used to treat bloat.
- Biphasic increase in pressure in the esophagus is observed during eructation. In the first phase, gas enters the esophagus. In the second phase,sharp increase in pressure accompanied by esophageal contraction.
- High grain feeding and feeding of lush alfalfa results in trapping of gases in the rumen called “ feedlot bloat” or “legume bloat”. This is due to formation of foam in the ruminoreticulum which traps many small gas bubbles. This can be prevented by reducing feeding of grains or lush pastures.
Nervous control of ruminal contraction
Cyclical contractions of the first three compartments which begins early in life continue through out life without any interruption.
Cyclical contractions are disturbed during pathological conditions affecting firstly rumen (impaction, intestinal intussusceptions) resulting cessation of rhythmic spontaneous contractions.
Smooth muscle fibres of rumen receives sympathetic and parasympathetic (vagus) innervations which provide rhythmic propulsive motility.
Rumination is an indicator of good health because of all the nervous pathways and neuromuscular functions of the stomach must be functioning well forexecution of the complex rumination reflex.
The ruminal stomach is supplied with an extensive network of afferent nerve fibres that carry information from in the stomach to the CNS. Tension receptors are more in reticulum and cranial sac.
Epithelial receptors are more in reticulum and cranial sac and pillars of rumen. Mucosal receptors are rich in abomasum and duodenum and are sensitive to both mechanical and chemical stimuli.