Optimizing Vitamin D3 Supplementation to Prevent Tibial Dyschondroplasia (TD) in Poultry-Comparative landscape of Calcitriol as compared to other vitamin D3 derivatives

Introduction:

The poultry industry plays a crucial role in global food production, providing a primary source of animal protein through meat and eggs. However, intensive poultry farming has led to the rise of skeletal disorders such as Tibial Dyschondroplasia (TD), a metabolic bone disease commonly found in fast-growing broiler chickens. TD affects the growth plates of long bones, leading to lameness, poor weight gain, and high economic losses. One of the key nutritional factors influencing TD development is vitamin D and its metabolites, which are essential for bone mineralization and chondrocyte differentiation. This article explores the role of vitamin D in TD prevention, focusing on bioavailability, biopotency, and dietary optimization.

Understanding Tibial Dyschondroplasia (TD) in Poultry:

TD is a skeletal disorder affecting the growth plates at the ends of long bones, particularly the tibiotarsus and tarsometatarsus. It is characterized by the presence of unmineralized, avascular cartilage, which fails to mature into bone.

Key Pathogenic Mechanisms of TD:

1. Impaired Endochondral Ossification
   • In normal bone development, chondrocytes proliferate, mature, and are replaced by bone.
   • In TD, chondrocyte differentiation is disrupted, leading to cartilage accumulation.
2. Failure of Cartilage Vascularization
   • Growth plate blood vessels fail to penetrate, preventing nutrient supply and ossification.
   • Hypoxia and cell death contribute to defective mineralization.
3. Oxidative Stress and Cellular Damage
   • Increased reactive oxygen species (ROS) damage chondrocytes.
   • Antioxidant defenses (glutathione, catalase) are often overwhelmed.
4. Nutritional Deficiencies and Genetic Susceptibility
   • Calcium, phosphorus, vitamin D, and trace mineral imbalances (Zn, Cu, Mn) affect bone formation.
   • Some genetic lines of broilers are more prone to TD due to rapid growth rates.
5. Disruptions in Molecular Signaling
   • Altered expression of growth factors (VEGF, IGF-1, Indian Hedgehog) affects cartilage formation.
   • Matrix metalloproteinases (MMPs) responsible for cartilage degradation may be dysfunctional.

The Role of Vitamin D₃ in Bone Health and TD Prevention:

Vitamin D plays a vital role in bone mineralization by regulating calcium and phosphorus metabolism. Its active form, 1,25-dihydroxyvitamin D₃ (calcitriol), is crucial for:

• Chondrocyte differentiation and proliferation in the growth plate
• Enhancing calcium and phosphorus absorption from the intestines
• Promoting vascularization and cartilage-to-bone transition.
• Preventing the accumulation of unmineralized cartilage, reducing TD risk.

Vitamin D Metabolism in Poultry:

• Vitamin D (Cholecalciferol) is converted in the liver to 25-hydroxyvitamin D₃ (25-OH-D₃).
• In the kidneys, 25-OH-D₃ is hydroxylated to 1,25-dihydroxyvitamin D₃ (Calcitriol – the active form).
• The active form binds to vitamin D receptors (VDRs) in bones and intestines to regulate calcium uptake and bone mineralization.

Bioavailability and Biopotency of Vitamin D Vitamers in Poultry

Different forms of vitamin D vary in their ability to be absorbed and utilized in poultry.

Comparison of Vitamin D Vitamers:

Vitamer	Conversion Steps	Bioavailability	TD Prevention Effectiveness
Vitamin D₂ (Ergocalciferol)	Liver → 25-OH-D₂ → 1,25-(OH)₂-D₂	Low	Poor
Vitamin D₃ (Cholecalciferol)	Liver → 25-OH-D₃ → 1,25-(OH)₂-D₃	Moderate	Good
25-Hydroxyvitamin D₃ (25-OH-D₃)	Absorbed as 25-OH-D₃	Higher	Very Good
1,25-dihydroxyvitamin D₃ 1,25-(OH)2-D3	Directly absorbed as active metabolite	Ultra-high	Excellent

Why 1,25-(OH)₂ -D₃ (Calcitriol- D) is More Effective Than Standard D₃:

• Bypasses the all-hydroxylation steps being already active form, allowing for faster absorption and utilization.
• Reduces TD incidence, improves bone strength, and enhances overall growth performance in broilers.

Physiological Roles of 1,25-(OH)₂-D₃:

• Enhances calcium and phosphorus absorption from the intestines.
• Stimulates chondrocyte maturation and endochondral ossification in the growth plate.
• Regulates vascularization and mineral deposition in cartilage.
• Binds to vitamin D receptors (VDRs) in bone-forming cells to promote skeletal integrity.

Scientific Evidence Supporting 1,25-(OH)₂-D₃ in TD Reduction:

Numerous studies have demonstrated the role of vitamin D₃ and its derivatives in preventing TD and promoting bone health:

• Lidor et al. (1987): Direct injection of 24,25-dihydroxyvitamin D₃ into rachitic chick growth plates resulted in healing, highlighting its direct action on chondrocytes.
• Boyan et al. (2002): Found that 1,25-(OH)₂-D₃ decreased chondrocyte proliferation in both resting and proliferative zones, ensuring proper cartilage turnover.
• Atencio et al. (2005), Driver et al. (2005): Showed that dietary supplementation with 1,25-(OH)₂-D₃ and its analogs significantly reduced TD incidence in broiler chickens.

Optimizing Vitamin D Supplementation in Poultry Diets:

To effectively prevent TD and enhance bone health, poultry feed should include:

• Adequate vitamin D₃ (Cholecalciferol) supplementation to meet metabolic requirements.
• Use of 1,25-dihydroxyvitamin D₃ (1,25-(OH)₂-D₃) as a more bioavailable alternative.
• Phytase enzyme supplementation to enhance phosphorus availability.
• Balanced calcium and phosphorus levels to support proper bone development.

Recommended Dietary Inclusion Levels:

• Vitamin D₃: 3,000 – 5,000 IU/kg feed.
• 1,25-(OH)₂-D₃: Inclusion through fortified supplements if needed.
• Calcium-to-Phosphorus Ratio: Maintain at 2:1 for optimal bone mineralization.

Conclusion:

1,25-Dihydroxyvitamin D₃ is a key regulator of bone mineralization and chondrocyte maturation, making it essential for TD prevention in poultry. Studies confirm its role in enhancing cartilage development, vascularization, and calcium-phosphorus homeostasis. Poultry diets optimized with 1,25-(OH)₂-D₃ can significantly reduce TD prevalence, improve skeletal strength, and enhance broiler productivity.

Note: Calcitriol-D – the king of all D3 – imported from Netherlands is available with GLOCREST Pharmaceutical Pvt Ltd in 20 kg premix form and 5kg concentrate form: For details, please contact Dr Ramdas S Kambale: 9820393342 or at ramdas@glocrestpharma.com