Livestock Digestive Systems: Monogastric and Ruminant

• The digestive system breaks down food, absorbs nutrients, and eliminates waste
• Livestock digestive systems vary with the animal's diet

Monogastric Digestive System (e.g., Pigs, Poultry)

• Monogastric animals have a simple, single-compartment stomach
• Digestion starts in the mouth with mechanical breakdown and saliva's enzymatic action
• The stomach stores, mixes, and starts protein breakdown using hydrochloric acid and enzymes like pepsin
• The small intestine is the primary site for enzymatic digestion and nutrient absorption
• The pancreas secretes enzymes like amylase, lipase, and trypsin into the small intestine for digestion
• Bile from the liver (stored in the gallbladder in some) emulsifies fats for absorption
• The large intestine absorbs water and electrolytes, forming feces
• Poultry have a crop for storage and a gizzard, a muscular organ for grinding food

Ruminant Digestive System (e.g., Cattle, Sheep, Goats)

• Ruminants have a four-compartment stomach: rumen, reticulum, omasum, and abomasum
• The rumen, the largest compartment, contains microorganisms (bacteria, protozoa, fungi) that ferment plant material
• Fermentation produces volatile fatty acids (VFAs), a primary energy source
• Microorganisms synthesize essential amino acids and vitamins
• The reticulum, closely linked to the rumen, aids in particle sorting
• The omasum absorbs water and some VFAs
• The abomasum is the "true" stomach, secreting hydrochloric acid and digestive enzymes
• Rumination involves regurgitating, re-chewing, and re-swallowing food to reduce particle size and increase surface area for microbial action
• Fermentation gases (methane, carbon dioxide) are eliminated through eructation
• Ruminants can digest cellulose and complex carbohydrates via microbial fermentation

Hindgut Fermenters (e.g., Horses, Rabbits)

• Hindgut fermenters have a simple stomach, similar to monogastrics
• The large intestine, especially the cecum, is enlarged for microbial fermentation
• Hindgut microbial fermentation produces VFAs, though absorption is less efficient than in ruminants
• Horses don't ruminate; fermentation after the small intestine limits microbial protein absorption
• Some hindgut fermenters (e.g., rabbits) practice coprophagy (eating feces) for extra nutrients, especially B vitamins and microbial protein

Avian Digestive System

• Avian species have unique digestive adaptations, lacking teeth and needing efficient processing
• The crop is a sac for food storage and moistening
• The proventriculus is the glandular stomach, secreting hydrochloric acid and pepsin
• The gizzard is a muscular organ with grit to grind food particles
• The small intestine is the main site for nutrient absorption, like in monogastrics
• Ceca are paired pouches at the junction of the small and large intestines, where some fermentation occurs
• The cloaca is a common chamber for digestive, urinary, and reproductive tracts
• Birds excrete uric acid as their primary nitrogenous waste, conserving water

Comparative Aspects

• Ruminants' complex digestive systems are adapted for fibrous plant material
• Monogastrics are suited for diets rich in digestible carbohydrates and proteins
• Hindgut fermenters use fibrous feeds but are less efficient than ruminants
• Digestive efficiency relies on feed composition, processing, and animal age/health

Digestive Enzymes

• Amylase breaks down starch into sugars, secreted by salivary glands and pancreas
• Proteases (pepsin, trypsin, chymotrypsin) break down proteins into peptides and amino acids; pepsin from the stomach, trypsin and chymotrypsin from the pancreas
• Lipase breaks down fats into fatty acids and glycerol, secreted by the pancreas
• Cellulase breaks down cellulose into glucose, produced by microorganisms in the rumen and hindgut, not by animals
• Lactase breaks down lactose into glucose and galactose, secreted by the small intestine

Absorption

• Absorption mainly happens in the small intestine, which has a large surface area from villi and microvilli
• Nutrients move across the intestinal epithelium into the bloodstream or lymphatic system
• Water is mainly absorbed in the large intestine

Waste Elimination

• Undigested food, bacteria, and metabolic wastes are excreted as feces
• Mammals eliminate feces through the anus
• Birds eliminate feces through the cloaca, along with uric acid

Factors Affecting Digestion

• Feed Composition: The type and quality of feed influence digestibility and nutrient availability
• Feed Processing: Grinding, pelleting, or cooking can improve digestibility
• Microbial Population: A healthy and diverse microbial population is essential for ruminant and hindgut digestion
• Animal Age/Health: Digestive efficiency may be reduced in young or sick animals