PS8-19. Effects of Aluminosilicate Supplementation on Fecal Starch Concentration and Starch Digestibility of Finishing Nellore Bulls.

Abstract Aluminosilicates have been used in feedlot diets because of their ion-exchange and adsorptive properties, which may improve starch utilization and reduce nutrient losses in high-concentrate systems. This study evaluated the effects of increasing doses of natural zeolite (NZ; 0, 1, 2, or 3% of diet DM) on fecal starch concentration of finishing feedlot cattle. Two hundred and fifty Nellore bulls (initial BW = 344 ± 15 kg) were allotted to thirty-two feedlot pens (experimental units) in a randomized complete block design. Cattle were fed once daily for 112 d. Fecal starch (FS, %) was evaluated on days 30, 60, and 90. Three samples were collected from three animals per pen immediately after defecation at 0800 h, taking care to sample only the upper portion of the fecal pad. Samples were immediately stored at − 20 °C. For analysis, samples were thawed and composited by pen and collection period. Animal identification was recorded to ensure sampling of the same animals across periods. Analyses were performed using a Total Starch K-TSTA Kit (Megazyme, Chicago, IL). Total-tract starch digestibility (TSD, %) was calculated according to Zinn et al. (2007). The statistical model included the fixed effects of treatment, sampling period, and their interaction. Data were analyzed using Tukey’s test, with significance declared at P ≤ 0.05 and tendencies at 0.05 < P ≤ 0.10. No effects of NZ supplementation or the interaction between treatment and sampling period were observed for FS or TSD (P > 0.05). However, sampling period affected both variables (P < 0.01). Fecal starch decreased from 30 d (3.80%) to 60 d (3.42%) and increased at 90 d (3.87%). Conversely, TSD increased from 30 d (98.47%) to 60 d (98.77%) and slightly decreased at 90 d (98.41%). These results indicate temporal variation in starch utilization across the finishing period. Supplementation with natural zeolite did not affect fecal starch concentration or total-tract starch digestibility in finishing Nellore bulls.