VPB 121: Veterinary Physiology - II (2+1)

RUMINANT STOMACH

• Ruminants are animals capable of regurgitating their food from their stomach and remasticate them.
• Capacity of the stomach varies with age and size of the animal.
• All herbivorous animals have spacious compartments in their G.I tract. It favours retention of bulky fibrous plant for soaking, mixing and  microbial fermentation.
• In ruminants and kangaroo, stomach(Rumen) provides an additional space for microbial fermentation.
• Bacteria, protozoa and fungi in the rumen are responsible for extensive fermentative digestion in the rumen. It is supported by the mechanical activity of the three compartments( rumen,reticulum and omasum). 
• Only the abomasum, the true stomach  secretes gastric enzymes and HCl. Ruminants are animals which can regurgitate and remasticate.
• Abomasum is the largest compartment in new born ruminants.
• As age advances, the rumen and reticulum grow at a faster rate than abomasum.
• In adults, rumen and reticulum occupies 69%, omasum 8% and abomasum 23% of the stomach portion. View image...
• Omasum is not well developed in sheep and goat, it is absent in Camel and Llama(Tylapoda)
• Oesophagus opens into the rumen through cardia.
• Rumen has two sacs, dorsal and ventral sacs that are freely communicating with each other.
• Rumen is connected to reticulum by rumino – reticular folds.
• Reticulum is communicated with omasum through reticulo –omasal orifice.
• Oesophageal/reticular groove extends from the cardia to reticulo – omasal orifice.
• It is a gutter like invagination. This groove is more functional in young ruminants. View image...
• During suckling the receptors in the pharynx and mouth get stimulated causes reflex closure of reticular groove to conduct liquid and milk directly from the oesophagus into reticulo – omasal orifice, bypassing rumen and reticulum. 

• In calves,  reticular groove/oesophageal groove acts as a bypass route for the passage of milk directly from the oesophagus into the omasum and abomasum.
• Closure of this groove is mediated by behavioural, psychological resposed and also by chemicals.
• Administration of chemicals like NaCl, NaHCO₃, CuSO₄ and sugar solutions reflexly close this groove, but CuSO₄ is less effective in calf and older ruminants, but more effective in sheep.
• Sodium salts like NaHCO₃ (60ml of 10% solution) stimulates closure in calves.