2. Growth and Development of the Ruminant Gastro-Intestinal Tract   GI Tract development begins very early in gestation.   Ruminant enters life as a simple stomached animal; forestomach (reticulorumen, omasum) is non-functioning at birth   Only a few weeks are required for activation of the forestomach

3. Growth and Development of the Ruminant Gastro-Intestinal Tract   Rumen papillae begin growth and development early in gestation.   The process begins as a capillary loop at about 3 months of gestation.   The capillary loop pushes up the lamina to create the papillae of the ruminal surface which is detectable by the 5 th month of gestation.

4. Growth and Development of the Ruminant Gastro-Intestinal Tract   Individual GI tract organs develop at different rates during gestation   Early in gestation the rumen, reticulum and omasum develop faster than the abomasum.   Later in gestation the abomasum develops rapidly, so that at birth the abomasum is equal in weight to the entire forestomach.

5. Growth and Development of the Ruminant Gastro-Intestinal Tract   Rumen is small and flaccid, with a very thin wall. Is non-functioning at birth.   Reticulum is one-third the size of the rumen at birth. Also has a very thin wall. Is non-functioning at birth.   Omasum is a small bulbous structure on the abomasum. Is non- functioning at birth.   Abomasum is well developed and highly functional at birth. Comprises about 70% of stomach capacity at birth. At the Time of Birth

6. Growth and Development of the Ruminant Gastro- Intestinal Tract   After birth, all digestive organs continue to grow, with the rumen, reticulum, omasum and small intestines growing at the greatest rates.

7. Growth and Development of the Ruminant Gastro-Intestinal Tract   Under normal conditions, ruminants have access to vegetation from birth. Diet can have a large impact on development of the GI tract.   Three phases ruminant GI tract development   0 to 3 weeks of age: non-ruminant phase   3 to 8 weeks of age: transitional phase   8 weeks onward: adult ruminant Figure is stomach of new born calf. Note size of abomasum relative to rumen.

8. Growth and Development of the Ruminant Gastro-Intestinal Tract Diet Milk OnlyHigh HayHigh Concentrate Concentrate fed, kg/day0.452.27 Live body weight, kg36.959.176.7 Ruminoreticulum weight, g2441,6782,120 Omasum weight, g54397410 Abomasum weight, g239405555 Intestines weight, g1,7785,3156,722 Effect of Diet on Gastro-Intestinal Tract Development

9. Growth and Development of the Ruminant Gastro-Intestinal Tract   Given access to pasture, ruminants begin to graze in the first week or two of life.   By four weeks of age:   Rumen is 4 to 8 times its birth weight.   Still an elastic sac without thickness of walls.   By eight weeks of age:   Animal’s body weight has doubled.   Period of rapid rate of rumen development.   Animal is heavily dependant upon the products of rumen fermentation.   By 8 to 10 weeks of age, development of the reticulorumen with respect to body weight is complete

10. Growth and Development of the Ruminant Gastro-Intestinal Tract   Tissues of the stomach consist of:   Outer layer of connective tissue (serous membrane).   Muscular tunic: aids in mixing digesta.   Rumen mucosa: inner surface of the mucosa is the epithelium.   Rumen epithelium serves in the absorption and metabolism of minerals and volatile fatty acids (VFA’s). Also protects the underlying rumen mucosa tissue.   Rumen papillae develop from the epithelium. Papillae increase the surface area for absorption of VFA’s.