VAN 211: Veterinary Histology and Embryology (2+2)

RUMINANT STOMACH

• Monogastric days reached in 33 days and 90^o rotation is completed by this time. The area corresponding to fundus becomes rumen. Other differential growth area appears along the greater curvature of embryo stomach just caudal and ventral to the forming rumen. This area is the reticulum.
• A third area appears along the lesser curvature. This is the omasum. The abomasum forms from the pyloric region. By 40 days, further differentiation occurs by two cranially directed outgrowths from fundus. One is dorsal and the other is ventral (dorsal and ventral sacs).
• By 43 days, rumen is growing caudo-dorsally and forward to the right. This results in reversal positions of the dorsal and ventral sacs. The sacs become directed caudally and the dorsal sac is dorsal to the ventral sac. Now the rumen is on the left side of the abdominal cavity, followed by reticulum, omasum and abomasum towards right.
• When the rumen enlarges, it forces the reticulum cranially and ventrally. As the rumen grows, it begins to encroach toward the right. This encroachment pushes the omasum and abomasum ventrally.
• Once the adult positions are reached (14 weeks of gestation) the growth of the rumen slows. By birth rumen is 1 1/2 size of abomasum. After birth rumen enlarges till 8 weeks and by 12 weeks, becomes twice the size of abomasum. In adults around 1- ½ yrs of age the size depends on roughage diet.