Growth and Development of the Ruminant Gastro-Intestinal Tract

1. Growth and Development of the Ruminant Gastro-Intestinal Tract Development of Rumen Papillae • Papillae develop from the lamina propria of the rumen lining Cross section of the rumen Serous membrane Muscular tunic Rumen mucosa Contains epithelial layer and lamina propria

2. Growth and Development of the Ruminant Gastro-Intestinal Tract Development of Rumen Papillae • Papillae develop from the lamina propria of the rumen lining Cross section of the rumen Epithelial layer Lamina propria • Papillae begins as a capillary loop pushing up the lamina propria and the epithelial layer to form the papillae.

3. Growth and Development of the Ruminant Gastro-Intestinal Tract Factors Affecting Rumen Development • Reticulorumen growth is delayed (inhibited) by all milk diets. Rumen from a 6 week old calf fed milk only. Note thin walls of rumen and minimal papillae growth.

4. Growth and Development of the Ruminant Gastro-Intestinal Tract Factors Affecting Rumen Development • Hay, forage, fiber stimulates reticulorumen development and growth through increased musculature of the rumen walls and papillae growth. • Addition of concentrates to hay diets increase papillae development due to increased production of VFA’s from microbial fermentation. Rumen from 12 week old calf fed milk plus hay Rumen from 12 week old calf fed milk, hay and concentrate

5. Growth and Development of the Ruminant Gastro-Intestinal Tract Factors Affecting Rumen Development

6. Growth and Development of the Ruminant Gastro-Intestinal Tract Factors Affecting Rumen Development • Addition of bulky inert materials to the rumen increases rumen muscular growth and volume, but does not enhance papillae growth because there is no increased fermentation. • Salts of VFA’s introduced directly into the rumen enhance papillary and epithelial development but do not stimulate growth of muscle tissue. • Butyrate is most effective in stimulating papillary growth followed by propionate and acetate. • Butyrate and propionate are most readily absorbed by the rumen epithelium. • Concentrate feeding causes a shift in the microbial population. • Increased microbial production of stronger acids (butyrate and propionate) decreases rumen pH.

7. Growth and Development of the Ruminant Gastro-Intestinal Tract Factors Affecting Rumen Development Study Investigating form of dietary forage (long vs pelleted; pelleted diets were either high fiber or low fiber) • Treatments: • Hay fed in long form • High fiber pellet • Low fiber pellet Normal tongue like papillae wee present in calves fed long hay.

8. Growth and Development of the Ruminant Gastro-Intestinal Tract Factors Affecting Rumen Development Study Investigating form of dietary forage (long vs pelleted; pelleted diets were either high fiber or low fiber) • High fiber pellet Papillae varied much more in shape with a higher proportion rounded in form and with keratinization of their tips

9. Growth and Development of the Ruminant Gastro-Intestinal Tract Factors Affecting Rumen Development Study Investigating form of dietary forage (long vs pelleted; pelleted diets were either high fiber or low fiber) • Low fiber pellet Papillae were small, nodular, cauliflower shaped with narrow stalks, very dark color, heavily keratinized with ingesta packed between them

10. Growth and Development of the Ruminant Gastro-Intestinal Tract Factors Required for Rumen Development • Establishment of bacteria in the rumen. When the calf is first born there are no bacteria in the rumen. Within days, aerobic bacteria become established. As dry feed is consumed (two weeks), anaerobic bacteria begin to grow and fermentation begins. • Water intake. Anaerobic fermentation requires water. Milk intake through nursing shunts the rumen through the esophageal groove and goes to the abomasum. • Muscular action of the rumen. Rumen contractions, motility and rumination are required to pass digesta through the rumen to the abomasum and lower tract.

11. Growth and Development of the Ruminant Gastro-Intestinal Tract Factors Required for Rumen Development • Absorptive ability of rumen tissue. Varying factors affect rumen wall muscle development vs. development of epithelium and papillae. Primary stimulus to development of epithelium and papillae is presence of VFA’s. • Substrate available in the rumen. Hay and long fiber is needed to develop rumen wall muscle and rumen volume. Concentrates stimulate microbial fermentation and the production of butyrate and propionate and are needed for quick development of rumen epithelium and papillae.