Resumen de Dietary factors influencing calcium and phosphorus utilization in broiler chicken
Calcium and phosphorus are the two major macro-minerals required for proper growing performance and bone mineralization in poultry. Feed ingredients from plant sources contain very low amounts of Ca and P, mostly in phytate molecules. Thus, they are inadequate in meeting their requirements, and inorganic sources of Ca and P are usually added to poultry diets. The hydrolysis of phytate-P with exogenous phytase helps to decrease the incorporation of mineral sources, the environmental impact of broiler production, as well as the dietary cost. However, minerals can readily bind to phytic acid and form mineral phytate complexes that may be resistant to hydrolysis by phytase, depending on the pH values. The global aim of this thesis was to investigate dietary factors influencing Ca and P utilization by broiler chicks of different ages.
In order to achieve this objective, a series of seven trials (Chapters 4 to 8) were designed.
Trial 1 was designed to evaluate the interaction between dietary levels of Ca and non-phytate phosphorus (NPP, with 1,150 FTU of phytase) on broiler performance, bone ash and whole-body fractional retention of Ca and P from d 1 to 14 of life. Broilers achieved their greatest weight gain (WG) and bone mineralization with 0.7% Ca and 0.38% NPP. Increasing dietary Ca decreased performance and bone mineralization, especially of the low NPP diets. While increasing Ca reduced its fractional retention, the increase in the levels of dietary NPP steadily increased the fractional retention of Ca, likely through an increase in bone deposition.
The aim of Trial 2 was to screen the influence of different Ca sources (limestone, Ca chloride, and a fat-encapsulated tri-calcium phosphate, TCP) at four dietary levels of NPP (with 1,150 FTU of phytase) on performance, ileal digestibility of Ca and P, and bone mineralization in broilers. Calcium sources were also evaluated in vitro to measure acid-binding capacity (ABC) and Ca solubility at different pHs. Ca chloride showed the highest solubility of Ca and the lowest ABC. The FI and WG on d14 were higher with TCP and limestone than with Ca chloride. Calcium ileal digestibility was higher with Ca chloride than with limestone or TCP.
In Chapter 6, Trials 3 and 4 aimed to explore the influence of different sources of mono-, di- or tri-calcium phosphate on animal performance, bone mineralization and mineral retention in broilers. In Trial 3, no interactions were observed between the P source and the NPP levels for any variable; no differences were observed among P sources. In Trial 4, broiler chickens fed with higher levels of MCP and TCP showed an improvement in FI, WG and G:F (gain feed ratio) at different stages, as compared to lower levels of MCP. Tibia weight and ash were also higher for animals fed with high MCP and TCP than for chicks of the low MCP diet. No differences were observed between either source.
In Chapter 7, Trials 5 and 6 were designed to evaluate the efficacy of a new phytase and to compare different commercial phytases used at different levels in broiler diets. The inclusion of 1,000 FTU from the new phytase improved growth performance and bone mineralization in broilers up to d 35, reaching values no different of a diet supplemented with a 0.2% higher P content. No differences were observed among the phytase types.
Trial 7, in Chapter 8, was designed to screen the possible I nteraction between the Cu source (CuSO4 and Cu2O) supplemented at different levels on the utilization of Ca and P by broilers. The two Cu sources were also evaluated in vitro to measure Cu and phytic phosphorus (PP) solubility and PP hydrolysis by phytase at different pHs. The results showed that the use of 150 ppm Cu and 300 ppm Cu of Cu2O is adequate to ensure broiler growth performance and a lower Cu organ accumulation in comparison to CuSO4.
Taking the results all together, the use of high dietary levels of Ca and P or the use of highly soluble mineral sources can produce negative responses on bird performance and bone mineralization.
