By: A. Riasi (PhD in Animal Nutrition & Physiology)

2. Isfahan University of Technology, Isfahan, Iran Animal Nutrition on the Rangeland (Part 3) By: A. Riasi (PhD in Animal Nutrition & Physiology)

3. Digestive system of ruminants • Proper care of the land and its grazing animals requires a sound understanding of ruminant nutrition. • First we must understand how a ruminant animal (cattle, sheep, goats) digests plant matter.

4. Digestive system of ruminants • Millions of bacteria, protozoa, and fungi live in the rumen. • The microorganisms break down energy-rich plant parts, making them digestible for the host animal. • After digestion the forage in rumen and broken down into small pieces, it can pass through the reticulum and omasum.

5. Digestive system of ruminants • Then material passing into the abomasum, or “true stomach,” where digestion continues. • From the abomasums onward, the ruminant digestive system closely resembles other animal digestive systems with a small and large intestine, colon, and anus.

6. Ruminant digestive physiology Small intestine Rectum Cecum Rumen Esophagus Reticulum Omasum Colon Abomasum

7. Ruminant digestive physiology

8. Digestive system of ruminants

9. Digestive system of ruminants

10. Digestive system of ruminants

11. Digestive system of ruminants

13. Advantage of pregastric fermentation • Make better use of alternative nutrients • Cellulose • NPN • Ability to detoxify some poisonous compounds • Oxalates, cyanide, alkaloids

14. Advantage of pregastric fermentation • More effective use of fermentation end products • Volatile fatty acids • Microbial protein • B vitamins • Decrease in handling undigested residues • In wild animals, it allows animals to eat and run

15. Disadvantage of pregastric fermentation • Fermentation is inefficient • Energy • Loss Amount (% of total caloric value) Methane 5-8 Heat of fermentation 5-6

16. Disadvantage of pregastric fermentation • Fermentation is inefficient • Protein • Some ammonia resulting from microbial degradation will be absorbed and excreted • 20% of the nitrogen in microbes is in the form of nucleic acids

17. Disadvantage of pregastric fermentation • Ruminants are susceptible to toxins produced by rumen microbes • Nitrates Nitrites • Urea Ammonia • Nonstructural carbohydrates Lactic acid • Tryptophan Methyl indole • Isoflavonoid estrogens Estrogen

18. Ruminant digestive process • Nutrients absorbed from the digestive tract include: • Volatile fatty acids • Amino acids • Fatty acids • Glucose • Minerals • Vitamins

19. Ruminant digestive process • Digestion begins when an animal takes a bite from the pasture. • As the animal chews the feed is formed into a bolus (a packet of food capable of being swallowed). • Saliva is excreted, which further aids in swallowing and serves as a pH buffer in the stomach.

20. Ruminant digestive process • Ammonia can be absorbed into the animal’s system through the rumen wall, or can be consumed by bacteria to become microbial protein. • If adequate and suitable VFAs are present, NH3 is incorporated into microbial protein; otherwise, it is absorbed, particularly if the rumen pH is alkaline.

21. Ruminant digestive process • Once in the rumen, the feed begins to undergo fermentation. • Millions of microorganisms ingest the feed, turning out end products which serve as a major source of nutrients for the animal.

22. Ruminant digestive process • Some of the principle products formed are ammonia, methane, carbon dioxide, and volatile fatty acids (VFAs).