Ruminant Digestion Overview

Ruminant Digestion

• Ruminants are the largest percentage of domestic herbivores
• They have a 4-compartment stomach allowing the use of roughage (cellulose) as a source of energy
• Microbial populations ferment feeds

Chewing

• Rumen fills quickly and little time for chewing
• Rumination: Animals regurgitate food and re-chew
• The more fiber, the more rumination required
• Reduce particle size to improve surface area
• Rumination takes up about 1/3 of an animal's life

Young Ruminant Digestion

• Rumen is undeveloped in young animals
• Reticular groove creates a tube that bypasses the rumen and reticulum to keep milk out
• If the calf drinks milk too quickly, milk may rot in the rumen causing diarrhea
• The groove prevents milk from entering the rumen and becoming fermented

Rumen Digestion

• Develops in response to young animals eating solid food, as early as 6-8 weeks
• All food consumed by ruminants enters the reticulo-rumen, with 85-95% fermented to some degree
• Bacteria in the rumen digest carbohydrates (cellulose) and other plant material
• Volatile fatty acids (VFAs) produced in the rumen are absorbed through the rumen wall, providing 50-70% of required energy

Rumen Wall

• Rumen wall is covered with papillae
• Bacteria convert nonprotein nitrogen (urea) into bacterial protein
• Amino acids meet protein requirements
• Protein content is similar to soybean meal
• Energy, vitamin K, and water-soluble vitamins are also produced
• Essential fatty acids are also produced

Reticulum Digestion

• Lies in front and below the rumen
• No physical division between rumen and reticulum
• Site of microbial action like the rumen
• Pacemaker for rumen contractions
• Starts in the reticulum and spreads to the rumen
• Mixes rumen contents for microbial digestion
• Moves contents through the digestive tract
• Heavier particles settle, lighter ones float

Omasum and Abomasum

• Omasum absorbs water, electrolytes, and VFAs, reducing particle size of feed
• Abomasum is equivalent to the true glandular stomach
• Folds in the walls provide extra capacity for handling dietary fiber

4 Compartments

• Forestomachs are placed anatomically before the glandular stomach
• Lining is nonglandular, with no mucus or enzymes
• Abomasum is lined with a true mucus membrane
• Secretes gastric juices, and the tract from the abomasum is similar to monogastric animals

Eructation

• Mechanism for removing gases produced during microbial fermentation
• Approximately 600 liters of gas per day in a dairy cow
• Contractions in the upper sacs of the rumen move gases to the esophagus, which dilates, allowing the gas to escape
• Much of the gas goes to the trachea and lungs

The Fermentation Process

• Rumen microorganisms and ruminant animals live in symbiosis
• Dissimilar organisms live together or in a close association for the benefit of both
• Microbes digest feeds that animals cannot
• Animals provide warmth, moisture, food supply, waste removal, darkness, pH, and anaerobic environment
• Rumination reduces particle size and increases feed availability
• Contractions keep contents mixed

Fermentation Products

• Volatile fatty acids (VFAs) are a major product of ruminal fermentation
• Include acetate, propionate, butyrate, isobutyrate, and valerate, isovalerate
• VFAs provide 50-70% of total energy needs
• Acetate is a precursor to milk fat
• Propionate is the main source of glucose for brain function and milk production
• Butyrate is an energy source for rumen epithelium and nutrient absorption
• Much protein breaks down to ammonia and organic acids, used by microorganisms to synthesize amino acids (AAs) for use, allowing NPN sources to be used in diets to reduce costs, while heat is a major fermentation product

Fermentation Products (continued)

• Most plant sources are low in lipids
• Feeds lipids are not significantly changed during fermentation
• High levels of fat are bad for microbes, reducing their fermentation abilities

Advantages of Ruminant System

• Microbial fermentation can digest feedstuffs that the animal's enzymatic process cannot digest, such as prairie hay, corncobs, and wheat straw.
• Ruminants can convert low-quality feed into high-quality food products
• Microbes synthesize essential nutrients such as vitamins, amino acids (AAs), and fatty acids that would be excreted if fermentation occurred in the cecum

Disadvantages of Ruminant System

• Microbial fermentation may destroy essential nutrients in the feed, decreasing quality
• Fermentation requires and wastes large amounts of energy, with a portion lost as heat and gaseous products
• Animals are more susceptible to digestive upsets like bloat or acidosis

Nutrition in Wildlife

• Wild species do not require supplementation in their natural habitats
• Climate change, pollution, habitat alterations, invasive species, and human disturbances affect the environment in which wild animals live, causing habitat loss and decline of biodiversity.
• Understanding animal eating habits is crucial for species conservation in situ and ex situ populations (e.g., safaris, zoos, game farms) where nutrition ensures reproduction.

Developing Wild Species Diets

• Dietary habits, gastrointestinal morphology, and physiology of similar domestic species should be used to develop diets for wild species.
• Nutritional research on exotic species in the wild and in captivity alongside environmental factors influencing energy and nutrient need is essential.

Dietary Habits in the Wild

• Species adapt their diets to their environments
• Bulk and roughage grazers (large stomachs) eat low-quality feeds (mainly grass)
• Browsers (small stomachs) consume leaves, flowers, fruits, shrubs, and trees
• Intermediate feeders eat both grass and leaves, adapting their diets to different seasons and variable feed quality

GI Tract Morphology and Physiology

• Digestive tract morphology correlates with natural diet
• Presence of ruminoreticulum and cecum reflects qualitative nutrient requirements similar to cattle and horses, respectively
• A simple stomach with limited gut capacity is similar to that of a pig.

GI Tract Morphology and Physiology (continued)

• Extrapolating nutrient requirements from domestic species isn't always accurate as livestock goals (growth, milk, eggs) differ from wildlife conservation requirements
• Wild/exotic animals should be fed a maintenance diet
• Guidelines from captive animal research must be used cautiously due to their anecdotal basis.

In situ Conservation Supplementation

• Focus on providing necessary nutrients that are not supplied by the available forage
• Nutrients of concern in wild species may include energy, protein, and minerals