response of laying hens to diet inclusion of canola meal as influenced by die-tary nonphytate phosphorus level and microbial phytase supplementation

An experiment employing a factorial arrangement of three levels (0, 8 and 16%) of canola meal (cm), two levels (0.15 and 0.25%) of nonphytate phosphorus (npp), and two levels (0 and 450 unit/kg; as fed basis) of microbial phytase was conducted using 216 hy-line w36 laying hens from 39 to 47 weeks of age. the birds receiving cm consumed more (p < 0.05) feed than birds receiving corn-soybean meal (sbm) diets. during the second 4-week of the experiment (44 to 47 weeks of age), egg production and egg mass were lower (p < 0.05) for birds receiving corn-sbm diet containing reduced npp level; however, the adverse effects of reduced npp were overcome by phytase supplementation (p < 0.05). during the second 4-week (44 to 47 weeks of age) and over the whole experiment (39 to 47 weeks of age), production of abnormal eggs was increased (p < 0.05) by feeding reduced npp level; phytase supplementation decreased (p < 0.05) egg abnormali-ty only when added to this diet. at the first egg sampling (43rd week of age), egg shape index and eggshell thickness were increased (p < 0.05) by phytase supplementation. reduced npp level caused a lower eggshell thickness in hens fed corn-sbm diet (p < 0.05). at the second egg sampling (47th week of age), birds fed corn-sbm diets or reduced npp level produced eggs with lower (p < 0.05) shell thickness, whereas dietary phytase supplementation reversed these adverse effects (p < 0.05). reduced npp level increased serum thyroxine concentration in birds fed corn-sbm-cm di-ets (p < 0.05). the results showed that cm can be included in laying hen diets up to 16% during 39 to 47 weeks of age without any adverse effect on their health and productivity. moreover, the re-sults indicated that reduction of npp level in corn-sbm-cm diets had little effect on performance and eggshell quality. the adverse effects of lowering npp level in corn-sbm diets could be sub-stantially reduced by phytase supplementation.