Overview of Ruminants' Stomach
Ruminants are the even-toed ungulate herbivorous mammals capable of regurgitating food from their stomach for remasticating. They possess large compartmental gastrointestinal tract (rumen, reticulum, omasum, abomasum, and intestine), which favors handling of large amounts of fibrous plant materials.
The rumen harbors vast range of microbes enabling microbial fermentation of ingesta before exposing to gastric juices in abomasum. The rumen microbiota, consisting of bacteria, protozoa, fungi, and archea degrade the ingested fiber-based diets. The mechanical activity of rumen, reticulum, and omasum supports this degradation. Esophagus opens into the rumen through cardia. The rumen is composed of cranial sac, ventral sac, and ventral blind sac, which are freely communicated with one another. The rumen wall is covered with many finger-like projections known as papillae with 5 mm in length and 3 mm wide in cattle.In ruminants, abomasum is analogous to monogastric stomach and hence called as true stomach. Similar to the monogastric’s stomach, abomasum secretes gastric enzymes and HCl. Among the four-rumen compartments, abomasum occupies large space in newborn ruminants. However, the growth rate of the rumen and reticulum will be faster compared to abomasum as the age advances. After completing the growth, rumen and reticulum, omasum, and abomasum occupies 69%, 8%, and 23% of the stomach portion. The pictorial representation of bovine stomach development from birth to maturity is presented in Fig. 14.1.
The omasum component is not well developed in small ruminants and is completely absent in the animals belonging to the suborder tylopoda (Camel and Llama). Esophageal groove or reticular groove, a gutter like invagination, extends from the cardia to reticulo-omasal orifice. The stimulation of sensory receptors in the pharynx and mouth causes closure of reticular groove to bypass milk directly from esophagus into
Fig. 14.1 Bovine stomach development from birth to maturity. [The size of rumen increases as the age advances and reaches maximum size at maturity]
reticulo-omasal orifice avoiding rumen and reticulum. Closure of esophageal groove is mediated by psychological responses, behavioral patterns, and chemicals such as sodium chloride, sodium bi-carbonate, copper sulfate, and sugar solutions. Among these chemicals, copper sulfate is less effective in calves and older ruminants and more effective in sheep.
14.2