Reticulum (honeycomb) The second chamber of the ruminant stomach Honey comb Capacity – 16 L Reticulum structure pH as in the rumen The smallest and most cranial compartment Separated from the rumen with ruminoreticular fold Nails and other sharp objects that are catches by the reticulum can hurt the pericardium. They can be removed with rumen magnate or by surgery Mechanical digestion and microbial fermentation occur to breakdown food particles for absorption Small ruminants have a relatively larger reticulum compared to cattle.
Omasum (manyplies) Many plies The third chamber in the ruminant stomach Omasum structure Capacity - 8 L Located within the intrathoracic part of the abdomen The omasal canal passes between the reticulum and the abomasum Its mucosa is smooth except for particularly large papillae around the reticulo-omasal opening, Contains no glands The omasum has biphasic contractions, the first - expels fluid by squeezing the ingesta from the omasal canal between the lamella. The second - expels solids by mass contraction of the omasum, VFAs and water are absorbed in the omasum Bicarbonate ions are removed from ingesta to avoid altering pH of the abomasum Small ruminants have a rel ativelysmaller bean shaped omasum In cows the lower pole of the omasum contacts the abdominal floor below the costal arch. Abomasum (true stomach) The fourth chamber Capacity - 27 L Abomasum Abomasum pH - 2-3 epithelium An elongated pear shaped true stomach with a glandular lining Gastric glands are present in the mucosal layer in the pyloric region Is responsible for the chemical breakdown of food- similarly to the monogastric stomach Secretes hydrochloric acid and pepsinogen Its movements are slow - contractions occur first in the proximal part and are more forceful at the pyloric part Differs in its position within the abdomen, depending on fullness of the other chambers of the stomach, contractions of the rumen and reticulum to which it is attached and by age and pregnancy status Displacement of the abomasum to the left or to the right is a common disorder affecting dairy cows due to high concentrate feed In small ruminants the abomasum can contact the liver and is proportionately larger than in cattle In newborn animals it is responsible for 60% of digestion but in an adult ruminant only 8% of digestion occurs in the abomasum. LiveNutrition
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