Effects of the source and level of digestible phosphorus in the diet on performance and egg quality of brown laying hens from 64 to 76 weeks of age

We studied the influence of the source of phosphorus (P) and level of digestible P (dP) in the diet on performance and egg quality traits of brown hens from 64 to 76 wk of age. The diets were based on corn and soybean meal and all contained 4.1 per cent Ca. The design was completely randomized with 8 treatments arranged as a 2x4 factorial with 2 sources of P [monocalcium phosphate (MCP) and calcined bone phosphate (CBP)] and 4 levels of dP (0.27, 0.31, 0.35, and 0.39 per cent) as main effects. Each treatment was replicated 14 times and the experimental unit was an enriched cage with 6 hens. The experiment lasted for 12 wk (3 periods of 4 wk each). Egg production and hen mortality were recorded daily. Feed intake and body weight (BW) of the hens were determined by period and cumulatively. Egg weight was estimated by period by weighing all the eggs produced the last day of each week on trial. From these data, average daily feed intake, egg mass, feed conversion ratio, and BW gain (BGW) were calculated by period and cumulatively. Egg quality traits, including Haugh Units and shell resistance to breakage, were determined per cage in 8 eggs collected at random the last two days of each experimental period. In addition, the percentage of dirty, broken, and shell-less eggs was recorded in all eggs produced. Data were analized as a completely randomized design with source of P and level of dP of the feed as main effects, and the interaction between them was also analized. In addition, the effect of the level of dP on the different variables studied was partitioned into linear (L) and quadratic (Q) components. No interactions between main effects were detected for any of the traits studied and therefore, only main effects are presented. Neither source of P nor level of dP affected any of the productive traits studied, except BWG that increased (L; P less than 0.05) as the level of dP of the diet increased. An increase in dP of the diet from 0.27 to 0.39 per cent tended to reduce (L, P equal to 0.077; Q, P equal to 0.058) shell resistance to breakage. Haugh units decreased linearly (P less than 0.01) as the level of dP increased. The percentage of non-sealable eggs (dirty, broken, and shell-less eggs) was higher in hens fed CBP than in hens fed MCP (P less than 0.05). In conclusion, from 64 to 76 wk of age, hens might not require no more than 0.27 per cent dP in the diet for optimal egg production and egg quality. An excess of dP (less or equal to 0.39 per cent) might reduce shell quality. Hens responded similarly to both sources of P but the percentage of non-saleable eggs increased with the use of calcined bone phosphate