Effects of Corn Varying in Extractable Salt-Soluble Protein Content with Phytase and Xylanase Supplementation on Growth Performance and Nutrient and Energy Digestibility of Broilers Fed Diets Adequate in Calcium and Non-Phytate Phosphorus
Type of Degreedissertation
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Extractable salt-soluble protein content can be assayed rapidly to help identify corn that may have been improperly dried or stored. Research indicates a relationship between this variable and broiler performance. Identification of corn with submarginal nutritional value will be advantageous to nutritionists. However, it may be beneficial to identify strategies to mitigate losses in performance and economic returns. One potential strategy is to supplement diets with exogenous enzymes. Enzyme supplementation may reduce nutritional variability among sources of corn. The first experiment evaluated the relationship between chemical composition of corn and nutrient and energy utilization in broilers from 28 to 30 d of age. Six of 12 sources of corn with similar proximate composition but with extractable salt-soluble protein content (PS) that varied from 25.7 to 49.2%, were selected for use in ileal digestibility assays. Ileal digestibility of N (IND; apparent), CF, and starch did not differ (P > 0.05) among sources of corn. Salt-soluble protein concentration was correlated with ileal digestible energy (IDE) among the corns (r = 0.5; P ≤ 0.001). Ileal N and fat digestibility were correlated with IDE (r = 0.4 and 0.3, respectively; P ≤ 0.05). Apparent MEn ranged from 3,262 to 3,342 kcal/kg and was correlated with PS (r = 0.8; P ≤ 0.001) and IDE (r = 0.36; P ≤ 0.05). These results indicated that sources of corn with similar proximate composition may vary in their digestible energy content, and in such a situation PS may be used to differentiate sources of corn varying in IDE or AMEn. The second and third experiments evaluated extra-phosphoric effects on amino acid (AA) and energy digestibility (experiments 2 and 3) and growth performance (experiment 3) of broilers fed diets (adequate in Ca and non-phytate P) supplemented with phytase and xylanase. In both experiments, factorial arrangements of treatments were evaluated consisting of 6 phytase (0, 1,000, 2,000, 4,000, 8,000, and 16,000 FTU/kg) and 2 xylanase (0 and 16,000 BXU/kg) concentrations in experiment 2 and 4 phytase (0, 500, 1,000, and 2,000 FTU/kg) and 4 xylanase (0, 8,000, 16,000, and 32,000 BXU/kg) concentrations in experiment 3. In each experiment, phytase and xylanase did not interact in their effects on AA and energy digestibility (P > 0.05) and only phytase main effects were observed. Broilers fed diets supplemented with phytase at 1,000 FTU/kg had increased (P ≤ 0.05) apparent ileal digestibility (AID) of most amino acids (AA). No linear or quadratic effects of phytase were observed in experiment 2. In contrast, broilers fed diets supplemented with phytase in experiment 3 exhibited linear (P ≤ 0.05) increases in AID of AA but not apparent ileal digestible energy. However, supplementation with 2,000 FTU/kg phytase increased (P = 0.049) ileal digestible energy by 36 kcal/kg compared with the basal diet. Broilers fed diets with 1,000 or 2,000 FTU/kg consumed more feed and grew faster (linear P ≤ 0.05) than their counterparts fed diets supplemented with 0 or 500 FTU/kg of phytase. The fourth experiment evaluated the potential interaction between sources of corn varying in PS and dietary supplementation with phytase and xylanase. The experiment consisted of a factorial arrangement of 16 treatments with 4 sources of corn (varying in PS) with or without phytase (0 or 1,000 FTU/kg) and xylanase (0 or 16,000 BXU/kg). Eight sources of corn were obtained in a similar manner as experiment 1 and were evaluated for PS. Of the 8 sources, 4 with similar proximate composition but with varying PS were chosen for the experiment. Broilers were provided experimental diets from 1 to 9 and 24 to 29 d of age. From 10 to 23 d of age, broilers were fed diets that included the same enzyme concentrations as the experimental diets but with a common source of corn. From 1 to 9 d of age, main effects of corn, phytase, and xylanase were observed (P ≤ 0.05). Among source of corn, Corn D (the source with the lowest PS content ) had the lowest (P ≤0.001) IND and IDE. Phytase increased digestibility of N and energy (P ≤ 0.001); however, xylanase supplementation decreased digestibility of both (P ≤ 0.029). From 23 to 29 d of age, broilers fed diets with either corn A or D had reduced IND with phytase and xylanase in combination compared with phytase or xylanase alone (P ≤ 0.05). Supplementation with both enzmes reduced IDE of diets based on corn A or D compared with xylanase alone, or either enzyme alone, respectively (P ≤ 0.05). In conclusion, corn sources varying in PS content interacted with phytase and xylanase supplementation on ileal nutrient and energy digestibility in broilers at 29 d of age. Phytase supplementation increased ileal digestibilities but had a more pronounced effect from 1 to 9 d of age. Further research should focus on clarifying the use of exogenous enzyme supplementation to mitigate effects of corn with sub-marginal nutrient value on nutrient utilization of broilers.