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Multiple factors may influence responses to phytase inclusion in broiler diets; therefore, a Plackett and Burman (1946) factorial design was used to identify the influential factors (Table 1). Eleven variables were screened over 12 treatments (six replicate cages of six birds per treatment) at two levels. Broiler chicks were offered steam-pelleted diets based on maize or wheat and soybean meal with 1000 FTU/kg exogenous phytase from 7-28 days post-hatch and their growth performance met 2014 Ross 308 objectives. Outcomes are shown in Table 2 (significance was declared at P < 0.10). High levels of Ca (P < 0.0001), canola meal (P < 0.0001) and a xylanase and β-glucanase cocktail (P < 0.10) negatively influenced weight gain, whereas higher levels of digestible lysine (P < 0.0001), xylanase (P < 0.003), available P (P < 0.04) and wheat as the feed grain (P < 0.06) positively influenced weight gain. High levels of Ca (P < 0.05), canola meal (P < 0.02) and available P (P < 0.1) negatively influenced gain-to-feed ratio whereas high digestible lysine (P < 0.0001) positively influenced gain-to-feed ratio. Given the responses to digestible lysine, one possible implication is that phytase supplementation will be effective in low crude protein diets with less ‘intact protein’ and high crystalline amino acid contents. It is noteworthy that xylanase inclusion per se amplified phytase response in diets that were based on both maize and wheat. Contrary to expectations, phytate-P did not significantly influence performance. |
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