Browsing by Subject "InsP6 degradation"

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Interactive effects of feed particle size, calcium, and exogenous phytase on gastrointestinal phytate degradation and related traits in broiler chickens
(2025) Wolfrum, Stephanie; Rodehutscord, Markus
Phosphorus (P) is an essential element in maintaining the physiological mechanisms of poultry, making an adequate dietary P supply crucial. In plant-based feed ingredients commonly used in poultry nutrition, the primary form of P is phytate, any salt of phytic acid (InsP6). Enzymes that hydrolyze InsP6, such as phytases and phosphatases, are needed to release P from InsP6 for digestion and absorption. The extent to which P is released depends on the limited and variable endogenous enzyme capacity of poultry. Consequently, diets are often supplemented with costly mineral P sources derived from finite global rock phosphates to meet P requirements. Any unabsorbed P is excreted and contributes to environmental impacts. Incorporating exogenous phytases into poultry diets enhances the P release from InsP6, thereby enabling reduced use of mineral P supplements. To further improve P utilization and completely replace supplemental mineral P, it is essential to understand the effects on phytase efficacy, both single and interactive. Therefore, three studies were conducted to gain deeper insight into the InsP6 degradation and related characteristics along the digestive tract of broiler chickens, as influenced by dietary ingredients and their physical properties. Using coarsely ground feed particles in broiler diets improves digestive tract development and nutrient utilization. Coarse particles may therefore be beneficial for InsP6 degradation. Moreover, dietary coarse particles might mitigate the inhibitory effects of high dietary calcium (Ca) concentrations by lowering the pH in the digestive tract. The first study aimed to investigate the single and interactive effects of feed particle size and Ca concentration in the absence and presence of exogenous phytase on InsP6 degradation, prececal digestibility of P, Ca, and amino acids (AA), and retention of P, Ca, and nitrogen (N). Ross 308 broiler chickens received experimental diets from day 7 to 22/23 of life. Experimental diets differed in feed particle size (fine and coarse; 222 and 309 μm), Ca concentration (low and high; 4.9 and 7.2 g/kg), and phytase supplementation (0 and 1,000 FTU/kg). Prececal InsP6 disappearance increased with coarse particle size without phytase supplementation. Supplemented phytase removed such differences. Coarse particles were associated with higher gizzard weights and lower gizzard content pH compared to fine particles, whereas high dietary Ca concentration increased the pH of the gizzard content. Thus, the antinutritive effects of the higher dietary Ca concentration were not mitigated by using coarse feed particles, resulting in a reduction in prececal InsP6 disappearance and digestibility of P and most of the AA. Prececal AA digestibility increased with dietary coarse particles compared to fine particles. In the presence of phytase, high dietary Ca enhanced InsP6 disappearance in the crop. The first study found that dietary coarsely ground feed particles without supplemented phytase increased prececal InsP6 disappearance, but phytase supplementation compensated for this particle size effect. Accordingly, the objective of the second study was to determine the single and interactive effects of feed particle size and phytase level. Effects on growth performance, prececal InsP6 disappearance, prececal digestibility of P and Ca, and tibia characteristics were examined. From day 10 to 38 of life, Ross 308 broilers were fed experimental diets containing fine and coarse feed particles (434 and 729 μm) and without and with phytase supplementation (300, 600, and 1,200 FTU/kg). Particle size and phytase did not interact significantly concerning any measured trait. Contrary to expectations, finely ground feed particles increased prececal InsP6 disappearance and P digestibility, suggesting coarse grinding of rapeseed meal may not benefit birds. Growth performance, prececal InsP6 disappearance and related P digestibility, as well as tibia ash and breaking strength, were increased by phytase supplementation. This indicated that diets met the bird’s P requirement at the given total P level and 1,200 FTU phytase/kg, allowing the renouncement of feed phosphate in the grower and finisher phases without adverse effects on performance and bones. Based on a previous study that found a linear relationship between the dietary InsP6 concentration and the prececal InsP6 disappearance caused by supplemented phytase, the third study aimed to verify this indication of a constant prececal InsP6 disappearance per unit of supplemented phytase. This suggested that the efficiency of supplemented phytase was not affected by dietary InsP6 concentration. The study investigated the effects of dietary InsP6 concentration and phytase supplementation on gastrointestinal InsP6 degradation, prececal digestibility of P, AA, and Ca, and N-corrected metabolizable energy (MEN) in broiler chickens. Ross 308 broilers were provided with diets from day 14 to 22/23 of life. Dietary InsP6 was increased by substituting corn starch with a mixture of 50 % soybean meal, 20 % rapeseed meal, 20 % sunflower meal, and 10 % rice bran (oilseed meal-rice bran levels (ORL)). Experimental diets included four dietary InsP6-P concentrations (ORL1, ORL2, ORL3, and ORL4) and three phytase levels (500, 1,500, and 3,000 FTU/kg). Feed ingredient exchange led to additional diet alterations beyond changes in InsP6 concentration, including variations in P, crude protein, Ca, and fiber concentrations. Increasing ORL decreased the InsP6 disappearance in the crop. Prececal InsP6 disappearance and P digestibility decreased linearly with increasing ORL at 500 FTU/kg, whereas ileal myo-inositol concentration was unaffected. This indicated that the supplemented phytase was the limiting factor for the complete dephosphorylation of InsP6 to myo-inositol. At 1,500 and 3,000 FTU/kg, prececal InsP6 disappearance and P digestibility differed hardly among ORL but decreased with increasing ORL. A non-linear relationship was found at 500 FTU/kg when prececal InsP6 disappearance or ileal myo-inositol concentration relative to FTU was regressed against dietary InsP6. Such relationships were linear at 1,500 and 3,000 FTU/kg, suggesting that the efficiency of supplemented phytase to fully hydrolyze InsP6 to myo-inositol at 1,500 FTU/kg or higher was impaired by phytase level but not ORL. The cecal InsP6 concentration increased with ORL and decreased with phytase. Increasing ORL decreased the prececal digestibility of all AA (except cysteine) and MEN. In conclusion, conflicting effects on InsP6 degradation concerning feed particle size and its effects on endogenous and supplemented enzymes were found. This suggests that using coarsely ground particles in the feed may not be equally effective for all ingredients. Rapeseed meal is potentially less suitable than wheat or corn in coarsely ground form. Regardless of phytase level, coarse feed particles increased prececal AA digestibility. Due to the inconsistent results and a lack of studies regarding feed particle size effects on InsP6 degradation and prececal AA digestibility, further research is needed. The antinutritive effects of dietary Ca on InsP6 degradation and prececal AA digestibility could not be compensated for by using coarse feed particles. To maximize nutrient utilization, feed particle size should be adapted to the respective raw material, and dietary Ca should be as low as possible without risking a deficit, combined with phytase. Supplemented phytase at 1,500 FTU/kg or higher does not impair InsP6 degradation and prececal AA digestibility in response to increasing ORL. Thus, adjusting the phytase level to increased dietary InsP6 concentrations was not necessary under the conditions of this study, and further research is necessary.