Novel Biomarkers for Calcium and Phosphorus Metabolism in Breeder Hens and Broilers

Broiler breeder hens are subject to the dual expectation to not only maintain a high production of eggs for an extended time period, but to produce eggs which can support the life of chicks which will be used for either meat production or as parent stock. Egg fertility and hatchability are heavily influenced by the thickness of the egg shell, the mineral calcium carbonate shell of the egg necessary for protecting the embryo growing inside. Many factors affect egg shell quality including age of the hen, diet, environmental conditions, genetic strain, stress, disease, and nutrition. Laying hens will mobilize calcium from the medullary bone to synthesize the calcium carbonate of the egg shell and use the calcium they absorb from their diet to replenish this medullary bone. Phosphorus is necessary for many cellular functions in animals and it also affects the availability of calcium making the ratio between the two minerals crucial not only egg production but also bone and whole body health. Previous studies have indicated a phosphorus retention threshold in breeder hens and broilers, the point when the amount of available phosphorus in the diet begins to be released into the excreta instead of being utilized in the body. In order to gain further understanding of why this phosphorus retention exists many elements involved in the whole body homeostasis of calcium and phosphorus in laying breeders have been investigated. The first study involved 6 dietary treatments of diets which consisted of 6 graded levels of non phytate phosphorus (NPP) ranging from 0.15% to 0.40% NPP with increments of 0.05 to determine the amount of phosphorus necessary for optimal egg production and to find out FGF23’s involvement in the retention threshold of phosphorus. Results showed that between 0.20% and 0.25% NPP that phosphorus retention dropped from 33% to 26% while FGF23 levels increased from 0.15% to 0.20% NPP and remained at the same concentration regardless of further increases in NPP in the diet. In the second study the relationship between bone health and egg shell quality was studied through the use of biomarkers for Osteoblast and Osteoclast activity: Tartrate acid resistant phosphatase (TRAP), and Bone alkaline phosphatase (BAP) respectively in both breeder hens and their progeny. Breeder hens were selected upon egg shell quality through Dual Energy X-ray Absorptiometry (DEXA) and split into two groups with either good shell quality of specific gravity \u3e1.80 or poor egg shell quality with specific gravit