Introduction
Calcium (Ca) and phosphorus (P) are essential macro-minerals in broiler nutrition, playing a crucial role in skeletal development, metabolic functions, and overall growth performance. These minerals must be supplied in the right balance to maximize feed efficiency, promote strong bone formation, and prevent metabolic disorders. In India, where poultry farming is a rapidly growing sector, optimizing Ca and P nutrition is vital to improving bird health and farm profitability. The availability of mineral sources, variability in ingredient digestibility, and reliance on plant-based feeds necessitate precise supplementation strategies—including the use of phytase enzymes to enhance phosphorus bioavailability.
This article explores the latest advances in Ca and P nutrition for broilers, highlighting their
impact on growth, feed formulation, and sustainability in the Indian poultry industry.
Role of Calcium and Phosphorus in Broilers
Bone Development and Strength
Approximately 99% of calcium and 80% of phosphorus in a broiler’s body are stored in the skeleton. These minerals are indispensable for formation of strong, healthy bones capable of supporting rapid growth and high meat yield.
Metabolic Functions
Calcium plays a vital role in nerve transmission, muscle contraction, and blood clotting. Phosphorus is crucial for energy metabolism (ATP production), cellular function, and DNA/RNA synthesis (E. Humer et al., 2015).
Enzymatic and Hormonal Interactions
Vitamin D3 regulates the absorption of calcium and phosphorus, An imbalance of these minerals can hinder enzymatic processes essential for digestion and growth (Markus Rodehutscord et al., 2022).
Sources of Calcium and Phosphorus
Common feed ingredients providing these minerals include:
- Calcium: Limestone, dicalcium phosphate (DCP), monocalcium phosphate (MCP), meat and bone meal (MBM), and fish meal.
- Phosphorus: DCP, MCP, MBM, and plant-based sources (e.g., phytate phosphorus).
Calcium and Phosphorus Recommendations for Broilers
Broilers require different levels of calcium and phosphorus at various life stages. Breeding companies such as Cobb and Ross regularly publish standard nutrient specifications and update them based on ongoing research and field performance. In recent years, the recommended levels of both minerals—except during the early stages—have been slightly reduced.
The table 1 & 2 illustrate the current calcium and phosphorus recommendations according to Cobb and Ross guidelines. In practice, poultry nutritionists in India typically follow these standards or make slight adjustments based on local experience and farm-specific conditions.
The Importance of Balance: Total Calcium (Ca) to Available Phosphorus(P) Ratio
The interplay between calcium and phosphorus is so strong that an excess or deficiency of one mineral directly affects the utilization of the other. The recommended dietary ratio of Ca to P for broilers typically ranges from 1.5:1 to 2:1 (Rafael F. Sens et al., 2021). An imbalance can cause the following issues:
- Excess Calcium: Reduces phosphorus absorption, lowers feed efficiency, and impairs the digestibility of other nutrients like fats and proteins (Markus Rodehutscord et al., 2022).
- Excess Phosphorus: Leads to poor bone mineralization and hinders calcium retention (Laura Shiromi David et al., 2023).
Calcium, Phosphorus, and Vitamin D3 Synergy
Vitamin D3 plays a crucial role in the absorption of both calcium and phosphorus. A deficiency in vitamin D3 reduces calcium and phosphorus uptake, leading to bone disorders like rickets and poor growth performance. There is an inverse relationship between vitamin D3 levels and mineral requirements—higher dietary vitamin D3 allows for slightly reduced levels of calcium and phosphorus.
Dietary supplementation with 25-(OH)2-D3 positively impacts performance, tibia ash, and serum concentration of calcium and phosphorus. This supplementation can also spare some available phosphorus in the diet, even phytase enzymes are included (accounting for calcium, available phosphorus, and sodium matrix). In many cases, the phosphorus-sparing effect of 25-(OH)2-D3 occurs without any noticeable changes in tibia morphology. At 250 mg/kg 1,25(OH)2-D3 can spare almost 0.1% available phosphorus, which equates to about 6 kg of Di-Calcium Phosphate (DCP) per ton of feed.
Vitamin D and its metabolites 25-(OH)-D3 and 1,25-(OH)2 -D3—have numerous functions in the avian system, though most attention is focused on calcium and phosphorus metabolism, bone health, and eggshell structures of broilers and layers. Plant sources of vitamin D are insufficient to meet the full needs of birds. Technically, dietary supplementation with 1,25-(OH)2-D3 is more effective than 25-(OH)-D3 in alleviating negative effects associated with calcium and phosphorus imbalances and dietary vitamin D deficiency. In broilers 1,25-(OH)2 -D3 can help reduce or potentiate the requirement for available phosphorus. Weak chicks at hatch and those facing management challenges benefit the most from this supplementation.
Phytate Phosphorus Neutralization and Phytase Matrix Consideration
A significant portion of phosphorus in plant-based feed ingredients—such as corn and soybean meal—is bound as phytate, which is poorly digestible by broilers. In Indian poultry diets relying on vegetable ingredients, up to 70% of phosphorus exists as phytate-P, bound to phytic acid molecules and thus unavailable for digestion and absorption. Typical phytate levels in corn- and soybean meal-based diets range from 2.5 to 4.0 g/kg. This can negatively impact growth performance and feed efficiency, as phytate can form complexes with proteins, amino acids, and other minerals (Rafael F. Sens et al., 2021).
Analyzing the phytate levels in diet is very important while formulating. Ingredients like rice polish, deoiled rice bran (DORB), cottonseed extract, rapeseed meal, wheat bran, and sunflower meal have high phytate content. Maize gluten meal, groundnut extract, and soymeal contain moderate levels. Typically, phytate levels range between 0.18–0.30% in broiler diets and 0.30–0.50% in layer diets. The use of alternate ingredients often raises phytate levels, which can impact other essential nutrients and overall performance. This can be mitigated by adding an effective phytase at higher doses.
Phytases hydrolyze phytate into free myo-inositol and six molecules of inorganic phosphate. This degradation improves phosphorus and calcium digestibility, tibia ash content, weight gain, and feed efficiency (J. I. M. Fernandes et al., 2019). Increasing phytase levels intensifies phytate elimination from the gastrointestinal tract.
Proper phytase matrix application requires analyzing the phytate content of the actual feed raw materials used. It is recommended not to apply the phosphorus matrix beyond 90% of phytate levels in diets.
The effects of phytase on amino acid and mineral digestibility other than phosphorus vary in the literature (Lagos et al., 2023). Experience and a holistic approach involving other enzyme matrices are essential for making informed decisions. Understanding the digestibility and requirements of antagonistic feed components, such as calcium, is necessary to avoid over-supplementation.
Phytase matrix values are specific to the phytase source and depend on factors such as enzyme stability during feed pelleting and passage through the gastrointestinal tract, as well as the enzyme’s efficiency in degrading inositol hexakisphosphate (InsP6) and its lower esters in the gut environment.
High Calcium Levels and Their Hidden Costs
Excess dietary calcium binds with phytates, reducing phosphorus bioavailability and protein digestibility.
Excess calcium in broiler diets often arises from multiple sources:
- Ingredient adulteration (e.g., soy and other ingredients contaminated with limestone powder (LSP))
- Water in Indian farms, which generally contains high Total Dissolved Solids (TDS) and calcium levels between 100–200 mg/L
- Use of additives with LSP as a carrier
- Ingredient adulteration with soil
- LSP, being inexpensive, is sometimes used as a filler in premixes and complete feeds
While adding more calcium might seem beneficial, overloading broiler diets has several hidden drawbacks:
- Lower Feed Intake and Growth: Excess calcium depresses feed consumption, slowing growth rates.
- Compromised Gut Health: Acidifiers added during stressful periods to control gut pathogens become less effective, as high calcium raises gut pH (Laura Shiromi David et al., 2023).
- Reduced Fat Absorption: Calcium binds dietary fats, forming indigestible “soaps” that hinder fat absorption.
- Impaired Protein Digestion: Calcium binds proteins in the lower gut, resulting in undigested residues in droppings.
- Mineral Imbalances: High calcium disrupts absorption of essential minerals like phosphorus, magnesium, manganese, and zinc, forcing nutritionists to adjust premix formulations. For example, a 0.1% increase in dietary calcium can reduce phosphorus digestibility by 4% (J. I. M. Fernandes et al., 2019).
Managing calcium levels carefully is critical to optimize nutrient utilization and maintain broiler health and performance.
Formulating Diets with Digestible Calcium and Phosphorus Specifications
Currently, broiler diets are formulated based on total calcium and available phosphorus. However, there is a growing focus on shifting towards formulation using digestible calcium and digestible phosphorus levels to optimize performance and profitability. This approach is theoretically more precise but faces challenges globally and in the Indian subcontinent.
Variability in Ingredient Digestibility:
The digestibility and mineral content of key ingredients like dicalcium phosphate (DCP), monocalcium phosphate (MCP), and limestone can vary widely due to differences in processing methods, raw material sources, and quality. For instance:
- Phosphorus digestibility in DCP ranges from 85% to 90%, depending on its origin.
- Limestone’s calcium digestibility is influenced by its solubility, which varies with particle size and purity.
- In plant-based ingredients such as corn and soybean meal, a large proportion of phosphorus exists as phytate, which is indigestible unless phytase are added. Moreover, the phytate content itself varies, complicating accurate diet formulation.
Moving towards digestible mineral specifications requires better characterization of ingredient variability and more consistent feed quality control. Despite these challenges, adopting digestible calcium and phosphorus standards can lead to improved nutrient utilization, better bird health, and enhanced farm profitability.
Lack of Accurate Digestibility Data (Published and Real-Time)
Many feed ingredients lack standardized, published data on digestible calcium and phosphorus levels. Nutritionists often rely on generalized or outdated values, which can lead to inaccuracies in diet formulation. Moreover, published digestibility values for the same ingredient can vary widely, complicating precise nutrient balancing.
Limestone Solubility and Its Implications
Limestone is one of the most common and cost-effective sources of calcium in broiler diets. However, its solubility significantly affects calcium availability and, consequently, broiler health and performance.
Solubility and Particle Size
Limestone solubility is largely influenced by particle size and the ore source. Fine particles dissolve quickly in the gut, releasing calcium rapidly, which is essential for early growth stages. In contrast, coarse particles dissolve more slowly, providing a sustained calcium supply over time.
- Fine Limestone: Highly soluble, suitable for meeting the early calcium requirements of broilers.
- Coarse Limestone: Less soluble, preferred for maintaining calcium levels throughout the growth cycle.
In India, fine limestone is predominantly used, but incorporating more coarse limestone could better support sustained calcium supply and improve overall bird performance.
Role of Acid Binding Capacity
Fine-grinded limestone has a high acid-binding capacity, meaning it can neutralize stomach acidity. This property may sometimes interfere with the gut’s natural digestion process, particularly affecting the digestion of other nutrients such as protein and phosphorus.
Key Takeaways
- Calcium and phosphorus are foundational to broiler health, playing critical roles in skeletal growth and metabolic processes. Adjusting their levels according to life stage and environmental factors ensures optimal bird performance. Maintaining the correct Ca:P ratio is essential to avoid nutrient imbalances and maximize performance.
- Indian poultry diets are typically rich in calcium. Although adding extra calcium might seem beneficial, it can lead to several negative consequences.
- Supplementation with vitamin D and its metabolites, 25-(OH)-D3 and 1,25-(OH)2-D3, supports avian systems, particularly in calcium and phosphorus metabolism, bone health, and eggshell quality in broilers and layers.
- The use of effective phytase enzymes helps overcome the challenges posed by phytate-bound phosphorus in plant-based diets. Accurate application of the phytase matrix requires analyzing the phytate content of feed ingredients in actual use.
- The solubility and particle size of limestone greatly influence its nutritional efficiency and the overall health and performance of broilers.
- Global data on digestible calcium and phosphorus are not standardized, highlighting the need for generating region-specific data for Indian feed ingredients.
- Lameness in broilers and layers should be carefully investigated, as supplementing more calcium is ineffective in about 99% of lameness cases.
- By focusing on these critical minerals, poultry nutritionists can unlock the full potential of broiler diets, enhancing growth, feed efficiency, and profitability.
Conclusion
Optimizing calcium and phosphorus nutrition is essential for enhancing broiler performance, skeletal integrity, and feed utilization. As Indian poultry producers and nutritionists shift towards more efficient feeding strategies, it is vital to adopt precise mineral balancing by using digestible calcium and phosphorus values and incorporating phytase enzymes to improve phosphorus absorption. Over-supplementation of calcium can incur hidden costs, such as impaired nutrient digestibility and compromised gut health. Additionally, understanding the solubility and particle size of calcium sources like limestone can greatly enhance mineral utilization. With ongoing research and innovation, the Indian poultry industry can refine its approach to mineral nutrition, resulting in improved productivity, economic efficiency, and environmental sustainability.
References are available upon request.
by Dr. Vinod Koskewar, Premium Chick Feed and Dr. Sushant Labh, Kemin Industries South Asia
