Animal Nutrition: Nutritional Physiology of Rabbits

Nutritional Physiology of Rabbits

• Rabbits are monogastric herbivores with a specialized hindgut comprising an enlarged caecum and colon.
• Undigested nutrients from the small intestine are fermented in the caecum, making rabbits hindgut fermenters.
• Rabbit diets consist of roughages and concentrates, leading to high feed intake and rapid digestive transit.

Digestive System of Rabbits

• The upper digestive tract in rabbits functions similarly to other monogastric mammals.
• A unique feature is the dual function of the proximate colon, where liquid fractions are absorbed and solid waste is formed.
• Hard faeces are excreted primarily as lignin and cellulose, requiring roughage to maintain intestinal health.

Caecotrophy in Rabbits

• Rabbits produce two types of faeces: hard and soft (caecotrophes).
• Hard faeces are rich in large particles (lignin and cellulose), while soft faeces contain B-complex vitamins, bacterial protein, and volatile fatty acids.
• Ingestion of soft faeces directly from the anus is termed caecotrophy, crucial for B-vitamin supply.

Nutrient Composition of Hard and Soft Faeces

• Hard Faeces Dry Matter: 47%
• Soft Faeces Dry Matter: 34%
• Hard Faeces Crude Protein: 17%, Soft Faeces Crude Protein: 30%
• Hard Faeces Crude Fiber: 30%, Soft Faeces Crude Fiber: 18%

Digestibility of Nutrients

• Rabbit digestibility of protein from forages is higher than in other herbivores.
• Fibre digestibility is lower in rabbits compared to other herbivores, with less energy contribution from fibrous sources.

Fermentation in the Caecum

• Caecal contents consist of 60-70% acetic acid, 15-20% butyric acid, and 10-15% propionic acid.
• Rabbits derive up to 40% of maintenance energy from volatile fatty acids produced during fermentation.
• Gut bacteria synthesize sufficient B-complex vitamins and vitamin K, negating the need for dietary inclusion.

Energy in Rabbit Diets

• Energy content is a key factor influencing feed intake, necessary for maintenance, growth, gestation, and lactation.
• Primary energy sources are carbohydrates and fats, efficiently digested by rabbits.

Carbohydrates

• Source of energy comes from starch, sugars, and digestible fibre.
• Rabbits effectively digest starch from cereal grains without significant issues.

Fibre

• Rabbit diets should contain at least 15% crude fibre to support intestinal health and motility.
• Indigestible fibre is vital for digestive system function, especially in growing rabbits.
• Low-fiber diets can lead to intestinal problems, while high-fiber diets risk cecal impaction.

Lipids

• Dietary fat concentrations typically range from 2% to 2.5%, necessary for essential fatty acids.
• In intensive systems, fat may be increased from 1% to 3%; added especially in lactating does' diets to enhance energy.
• Fat supplementation for weaning rabbits may improve body condition and immune system development.

Protein and Amino Acids

• Adequate dietary essential amino acids are crucial for rapid growth in rabbits.
• Bacterial protein synthesis in the caecum contributes minimally to essential amino acid needs in young rabbits, aiding nitrogen equilibrium in adults.
• Key amino acids for growing rabbits include lysine, methionine, and arginine.

Minerals

• Lactating does require higher dietary calcium due to calcium-rich milk.
• Bacterial activity makes plant phosphorus bioavailable; phytate phosphorus is efficiently utilized.
• Newborn rabbits have significant iron reserves, reducing dependency on dietary iron initially.
• Vitamin E is more critical than selenium for protecting against peroxide damage.
• Rabbits utilize cobalt efficiently for B12 synthesis through gut bacteria.

Vitamins

• B-complex vitamin requirements are partially met through caecotrophy practices.
• Fat-soluble vitamins should be supplemented in the diet for optimal health.