By: Dr. Khaled Okasha - PhD in Poultry Nutrition
Regional Technical Director for the Middle East, Danisco Animal Nutrition & Health (IFF)
Introduction:
Due to genetic improvements in breeder strains over recent years, it is essential to continuously review nutritional requirements. Both calcium (Ca) and phosphorus (P) are essential minerals for growth and bone formation, responsible for their hardness and strength. Therefore, accurately estimating calcium and phosphorus requirements is crucial for increasing productivity.
Unlike phosphorus (P), calcium sources are generally inexpensive. Studies have shown that excessive calcium may negatively affect digestion due to the formation of insoluble salts with dietary fatty acids in the intestinal lumen, which may reduce nutrient availability, decrease energy utilization, and reduce growth and feed efficiency. Additionally, excess calcium interferes with the digestion and absorption of trace minerals and interacts with inorganic phosphorus in the digestive tract. Hence, reducing calcium levels can enhance phosphorus utilization.
The Role of Calcium in Broiler Breeder Hens' Nutrition:
Calcium is one of the most abundant minerals in a bird’s body, with 99% of it located in the skeletal system. Laying hens require additional calcium for egg formation, drawing calcium from their bones. Each egg requires 2.5 grams of calcium and 0.7 grams of phosphorus.
Calcium plays a significant role in several physiological processes and has various functions. It exists in two forms:
Ionized form, which diffuses through membranes and exists as phosphate or bicarbonate.
Protein-bound form, which does not diffuse through membranes.
Key Functions of Calcium:
It is involved in the formation of bones and teeth.
Important for muscle contraction and relaxation.
Activates certain enzymes and participates in the secretion of several hormones.
Vital for egg shell formation.
Necessary for efficient growth.
Problems Caused by Calcium Deficiency:
Rickets
Muscle cramps or tetany (Calcium Tetany)
Reduced egg production and poor shell quality
Poor chick growth, weak bones, and osteomalacia, a condition resulting from calcium depletion from bones, often seen at peak egg production.
Calcium Sources:
Calcium levels in raw feed ingredients range from 2–30%, often in forms bound to oxalates (which are relatively unavailable).
Calcium Metabolism:
There is a well-established belief among nutritionists that diets high in calcium given to young breeder hens not yet producing eggs may negatively affect the metabolic system involved in calcium absorption and transport for egg shell formation. Excess calcium before egg production may trigger a physiological response to expel the excess calcium, resulting in a severe calcium deficiency when the bird’s calcium needs increase during egg production.
Calcium Requirements for Egg Production:
Calcium in each egg = 1.8 grams
Calcium digestibility factor = 60-70%
Therefore, the hen requires 3 grams of calcium to produce 1.8 grams for egg formation.
When a hen consumes 150 grams of feed per day containing 3.5% calcium, she ingests 5.25 grams of calcium, of which 3 grams are used for egg production.
Calcium Absorption:
Calcium absorption occurs through the intestines by passive diffusion when needs are low and the diet is high in calcium, or by active transport with vitamin D when needs are high and the diet is low in calcium.
Excessive calcium may interfere with the metabolism of other minerals, and calcium may be excreted in calcium-phosphorus (Ca-P) complexes, potentially leading to phosphorus deficiency. High sodium levels from drinking water may also interfere with calcium metabolism.
Role of Vitamin D3:
Active Vitamin D3 helps transfer calcium from bones to blood plasma. Its active form increases during ovulation, especially 4 hours after ovulation and continues for 10 hours, assisting calcium absorption through the formation of a calcium-binding protein (Calbindin) in the intestines. This protein keeps calcium in a soluble form until it passes through the intestinal cells.
Role of Phosphorus:
Phosphorus plays a vital role in the body, particularly in bone formation and its relationship with calcium and vitamin D. The balance between calcium and phosphorus is essential for efficient mineral metabolism and absorption.
Bone Growth:
Bones serve two functions: providing structural support for muscles and serving as a storage reservoir for calcium and phosphorus. Bone growth occurs at the growth plate, where osteoblasts secrete osteoid, a collagen-rich matrix that attracts calcium and phosphate ions to form bone crystals. Osteoclasts resorb bone minerals and organic material, helping to supply calcium and phosphorus to the body, especially during egg production.
Egg Shell Formation:
Egg shell formation takes about 25 hours, starting from ovulation. The initial 6 hours involve yolk and albumen formation, followed by calcium deposition on the inner shell membrane. Egg shell quality is highest when calcium comes from the diet rather than bone, as dietary calcium is more efficiently absorbed.
Calcium Requirements During Breeding and Production:
Before sexual maturity, calcium needs are low as bone growth is complete, and no egg production occurs. During production, each egg requires 1.7 grams of calcium, and hens may pull calcium from their bone marrow if dietary calcium is insufficient.
Calcium Sources for Poultry Feed:
Limestone and oyster shell powder are the primary and cheapest sources of calcium in poultry diets.
Special considerations must be made to ensure the sources are free from pathogens like Salmonella or E. coli and that the particle size is appropriate for absorption.
Calcium Particle Size and Its Impact:
Smaller calcium particle sizes (e.g., finely ground limestone) are absorbed quickly, but larger particles (e.g., coarse limestone or oyster shell) pass more slowly through the digestive tract, providing a steady supply of calcium during the night when egg shell formation occurs.
Heat Stress and Egg Shell Quality:
Heat stress can affect calcium metabolism, causing faster passage of feed through the digestive system, reducing calcium absorption. Additionally, heat stress increases panting, lowering CO2 levels in the blood, which reduces bicarbonate ions needed for calcium deposition on the shell.
Recommendations for Ross 308 Breeders:
Ensure sufficient calcium and phosphorus levels for skeletal development and production performance.
Provide 4-5 grams of calcium per day, with no more than 5% egg production rate.
To maintain shell quality, add 1 gram of calcium per bird daily in the form of large-particle limestone (3.2 mm).
Ensure calcium is available during the late afternoon for optimal shell formation.
Conclusion:
Ensuring adequate calcium intake is crucial for maintaining bone health, egg production, and shell quality in broiler breeder hens. Proper calcium management and understanding its interactions with other minerals and vitamins are vital for optimal poultry health and productivity.
English References:
Lessons, S. and J. D. Summers, 1997. Commercial Poultry Nutrition. University Books, Guelph, ON.
Korver, D. (1999). Prevention and Treatment of Calcium Tetany in Broiler Breeder Hens. Ross Tech.
Bradley J. Turner (2009). Calcium Tetany in Broiler Breeder Hens: Update. Aviagen Brief.
CALCIUM MANAGEMENT IN LAYER CONSIDERATIONS (Hy-Line Management Series)
Ross 308: Management Guide.
Arabic References:
Sami Alam, Diseases of Poultry and Their Treatment, 10th Edition, Anglo Egyptian Library.
Field Experiences of the Author.
