Age- Related Effects of Canola Meal and Digestibility Index Markers on Energy and Nutrient Utilization in Broiler Chickens

The objective of this thesis was to investigate the effect of age on energy utilization of canola meal using the regression method and evaluate the effects of age, marker, and analytical methods on nutrient digestibility in broiler chickens. Two studies were done to evaluate this objective. The first study was conducted to determine the ileal digestible energy (IDE), metabolizable energy (ME), and nitrogen-corrected ME (MEn) contents of canola meal (CM) for broiler chickens on days 8, 14, and 20 post-hatching using the regression method. Six hundred and twenty-four male Cobb 500 broilers were fed 3 experimental diets in which canola meal (CM) replaced energy ingredients in a corn-soybean meal-based reference diet at 0, 100, or 200 g/kg. The 3 diets were fed during the last 5 days of each of the 3 post-hatching days 8, 14, or 20 in a 3 x 3 factorial arrangement. Chicks were fed with experimental diets and grouped by weight into 8 replicates per treatment in a randomized complete block design. Excreta were collected during the last 3 days of each feeding post-hatching age, and ileal digesta on the last day of each period. The digestibility of dry matter (DM), nitrogen (N), energy, and IDE of the diet linearly decreased (P < 0.05) with increasing dietary levels of CM. Digestibility of DM, N linearly decreased (P < 0.001) and a quadratic reduction (P < 0.05) in energy and IDE with increasing age. There were linear and quadratic increases in total tract retention of DM, N, energy, ME, and MEn as the feeding age increased, and a linear decrease (P < 0.001) at increasing levels of CM inclusion. Regression-derived MEn values of CM as the age of birds increased were 1,630, 2,240, and 1,760 kcal/kg DM with the corresponding IDE values of 2,220, 2,230, and 2,910 kcal/kg DM and ME values of 1,810, 2,490, 2,000 kcal/kg DM for 8, 14 and 20 d, respectively. In conclusion, the study showed that utilization of energy and nitrogen in the CM is influenced by the broiler chicken age, and energy utilization in diets decreased with increasing inclusion levels of canola meal and increased with age of broiler chickens. The second study evaluated the effects of age, marker type, and analytical methods on nutrient digestibility in broiler chickens. Corn-soybean meal-based diets containing either chromium, titanium, or the combination of both markers were fed during the last 5 days of 3 experimental periods (d 7, 14, or 21), in a 3 × 3 factorial arrangement. Birds were grouped by body weight into 6 replicate cages per treatment in a randomized complete block design. Excreta were collected during the last 3 days of each period. Ileal digesta was collected on the last day of each period. The diets, excreta, and digesta collected were analyzed for chromium and titanium using an atomic absorption spectrophotometer and ultraviolet-visible spectrophotometer to determine the apparent ileal digestibility (AID), apparent total tract utilization (ATTU) of dry matter (DM), nitrogen (N), and gross energy (GE), apparent metabolizable (AME) and nitrogen corrected apparent metabolizable energy (AMEn). Data were analyzed using the GLM procedure of SAS. The main effects of age, marker type combination, analytical method, and their interactions were evaluated in a 3 × 4 × 2 factorial of 3 ages (d 7, 14, or 21), 4 maker type combinations (Cr2O3 alone, TiO2 alone, Cr2O3 in combination with TiO2, or TiO2 in combination with Cr2O3), and 2 analytical methods (atomic absorption spectrophotometry or ultraviolet-visible spectrophotometry). The means were separated using Tukey’s test. There was an age and method effect on AID and ATTU of all nutrients and energy evaluated, while marker effects varied, with significant difference on AID of DM, GE, N, ATTU of GE and N, and no effect on ATTU of DM, AME, and AMEn. There was an age × marker × method interaction (P