Monogastric Digestive System

• The digestive system breaks down feed into components usable by the animal
• Digestive systems vary among livestock species, influencing feeding habits and nutrient use
• Livestock digestive systems are broadly grouped into monogastric and ruminant systems

Monogastric Digestive System

• Monogastric animals possess a simple, single-chambered stomach
• Digestion starts in the mouth via mechanical breakdown and enzyme activity
• Salivary amylase is present in some monogastric species
• The stomach stores food, mixes it with gastric secretions, and starts protein digestion
• Gastric secretions include hydrochloric acid and enzymes like pepsin
• The small intestine is the primary site of nutrient absorption
• The duodenum, jejunum, and ileum make up the small intestine
• Pancreatic and intestinal wall enzymes further break down carbohydrates, proteins, and fats in the small intestine
• Bile from the liver helps emulsify fats
• The large intestine absorbs water and electrolytes, forming feces
• The crop in poultry acts as a storage organ
• The gizzard in poultry is a muscular organ for grinding feed
• Poultry have a cloaca where digestive, urinary, and reproductive tracts meet

Ruminant Digestive System

• Ruminants have a four-compartment stomach
• The four compartments of the ruminant stomach are the rumen, reticulum, omasum, and abomasum
• The rumen is the largest compartment, acting as a fermentation vat
• Microorganisms in the rumen (bacteria, protozoa, fungi) break down cellulose and complex carbohydrates
• The reticulum aids in particle sorting and regurgitation for further chewing (rumination)
• The omasum absorbs water and some minerals from the digesta
• The abomasum is the "true" stomach, secreting hydrochloric acid and pepsin for protein digestion
• Ruminants can use fibrous feeds due to microbial fermentation in the rumen
• Microbial fermentation produces volatile fatty acids (VFAs), a major energy source
• Microbes synthesize B vitamins and essential amino acids
• Rumination reduces particle size and increases surface area for microbial action
• Gases from fermentation (methane, carbon dioxide) are eliminated through eructation

Comparative Aspects

• Horses are hindgut fermenters, using a large cecum for microbial fermentation
• Hindgut fermentation in horses is similar to the rumen but less efficient
• Rabbits practice coprophagy to obtain nutrients from cecal fermentation
• Avian species lack teeth, relying on the gizzard to grind feed
• Monogastrics need higher-quality, readily digestible diets
• Ruminants can thrive on fibrous feeds
• Ruminants convert low-quality feeds into valuable products like meat and milk
• The efficiency of nutrient use varies among livestock due to digestive and metabolic differences
• Environmental factors influence digestive function and animal performance
• Diet composition and feeding management are key environmental factors
• Understanding livestock digestive systems is vital for formulating diets and optimizing animal health and productivity

Monogastric animals possess a single-chambered stomach. Digestion starts in the mouth and continues in the stomach with gastric secretions. The small intestine is the primary site for nutrient absorption, where enzymes from the pancreas and intestinal wall further break down carbohydrates, proteins, and fats.