MAMMALIAN NUTRITION Part II. Specialization of carnivores and herbivores RICHARD LLOPIS-GARCIA A2 BIOLOGY

OBJECTIVES Describe the specialization of teeth and digestive systems in a ruminant and a carnivore.

Quick Draw Quickly look at the herbivore and carnivore skulls and draw up a table to compare the number, shape, and possible function of each type of tooth Make some drawings and put labels on them.

Two worlds Roughly 50% of the organic carbon on earth is tied up in cellulose. This represents an enormous source of energy, yet vertebrate cells do not produce the cellulases necessary to break down this abundant material. However, many microbes do secrete cellulases which allow them to utilize dietary cellulose and other plant wall materials.

Two worlds Cellulolytic microbes inhabit the digestive tract of all animals, allowing the animal to siphon off and assimilate the end products of fermentation, particularly short chain or volatile fatty acids.

Two worlds The relative value of fermentation to an animal's nutrition pretty much depends on the size of its fermentation vat. Fermentation occurs in the colon of dogs and humans, but their large bowel is rather small and the benefit they gain from fermentation is trivial. In contrast, herbivores make a living on cellulose by possessing massive fermentation vats as part of their digestive tract.

Herbivorous Strategies Two distinct strategies have evolved. The chief difference between the two groups is in positioning of their fermentation vat relative to the stomach and small intestine:

Cranial fermentors or ruminants have a large, multicompartmented section of the digestive tract between the oesophagus and true stomach. These fore stomachs house a very complex ecosystem that supports fermentation. Examples of ruminants are cattle, sheep and deer.

Caudal fermentors or cecal digestors are “similar” to dogs and humans through the stomach and small intestine, but their large intestine, where fermentation occurs, is complex and exceptionally large. Examples of cecal digestors include horses and rabbits.

The process and outcome of fermentation is essentially identical in the rumen of a cow or the cecum of a horse. However, the positioning of the fermentation vat in relation to the small intestine has very important implications for animal's physiology and nutrition. These similarities and differences can be summarized as follows: Function Rumin ants Cecal Digestors Ability to efficiently digest and extract energy from cellulose Yes Ability to utilize dietary hexose sources directly NoYes Ability to utilize the protein from fermentative microbes YesNo

Fermentation Microbiology and Ecology Fermentation is supported by a rich and dense collection of microbes. Each milliliter of rumen content contains roughly 10 to 50 billion bacteria, 1 million protozoa and variable numbers of yeasts and fungi.

Fermentation Microbiology and Ecology Fermentative microbes interact and support one another in a complex food web, with the waste products of some species serving as nutrients for other species. Fermentative bacteria representing many genera provide a comprehensive battery of digestive capabilities ( e.g.. Cellulolytic (digest cellulose), Hemicellulolytic (digest hemicellulose), Amylolytic (digest starch), Proteolytic (digest proteins), Vitamin synthesizers, Methane producers )

Digestive Anatomy in Ruminants The stomach of ruminants has four compartments: the rumen, reticulum, omasum and abomasum Collectively, these organs occupy almost 3/4ths of the abdominal cavity, filling virtually all of the left side and extending significantly into the right.

The interior surface of the rumen forms numerous papillae that vary in shape and size from short and pointed to long and foliate.

Reticular epithelium is thrown into folds that form polygonal cells that give it a reticular, honey-combed appearance. Numerous small papillae stud the interior floors of these cells.

The inside of the omasum is thrown into broad longitudinal folds or leaves reminiscent of the pages in a book (a lay term for the omasum is the 'book'). The omasal folds, which in life are packed with finely ground ingesta, have been estimated to represent roughly one-third of the total surface area of the forestomachs.

Fermentation Microbiology and Ecology The distribution of microbial species varies with diet. Some of this appears to reflect substrate availability; for example, populations of cellulolytic bugs are depressed in animals fed diets rich in grain. Environmental conditions in the fermentation vat also can have profound effects on the microbial flora. Rumen fluid normally has a pH between 6 and 7, but may fall if large amounts of soluble carbohydrate are consumed.