PS8-20. Influence of Natural Zeolite Supplementation on Dietary Energy Utilization in Finishing Nellore Bulls.

Abstract Improving energy utilization remains a key challenge in feedlot systems, where small efficiency gains can substantially impact profitability and sustainability. Natural zeolites (NZ) are aluminosilicates characterized by high cation-exchange capacity and adsorption properties, which may influence ruminal fermentation and nutrient utilization. Reports in the literature indicate that NZ supplementation can increase dietary energy utilization by approximately 4.5% in feedlot cattle. However, responses remain inconsistent under high-concentrate feeding conditions. Therefore, this study evaluated the effects of increasing levels of NZ on the energy value of high-concentrate diets fed to finishing feedlot cattle. Two hundred and fifty Nellore bulls (initial BW = 344 ± 15 kg) were allocated to thirty-two feedlot pens (experimental units) in a randomized block design. Treatments consisted of increasing levels of NZ (0, 1, 2, or 3% of diet DM), replacing high-moisture corn (HMC) in the diets. Diets contained 20% corn silage, 45 to 48% HMC, 30% DDGS, and 2% mineral mix plus monensin (30 ppm). Cattle were fed twice a daily for 112 d. Observed net energy (NE) of the diets was calculated from animal performance (pen means for DMI, ADG, and shrunk BW) using the methodology described by Zinn and Shen (1998). Energy gain (EG) was calculated as EG = (0.0557 × BW^0.75) × ADG^1.097 (NRC, 1984), where EG represents retained energy (Mcal/d) and BW is mean shrunk BW. Maintenance energy expenditure (EM; Mcal/d) was estimated as EM = 0.077 × BW^0.75 (Lofgreen and Garrett, 1968). Net energy for maintenance (NEm) and Net energy for gain (NEg) were calculated according to Zinn and Shen (1998). Expected NEm and NEg values were estimated from tabular TDN values of feed ingredients according to NASEM (2016), using the respective NE equations and accounting for monensin inclusion. Ratios of observed-to-expected NEm and NEg were calculated. Data were analyzed using Tukey’s test with significance declared at P ≤ 0.05 and tendencies at 0.05 < P ≤ 0.10. Natural zeolite supplementation did not affect calculated NEm or NEg of the diets (P > 0.05). The calculated NEm values were 2.10, 2.03, 2.06, and 2.03 Mcal/kg for the 0, 1, 2, and 3% NZ inclusion levels, respectively. The mean NEg across treatments was 1.4 Mcal/kg. Likewise, the ratios of observed-to-expected NEm and NEg were not altered by NZ inclusion (P > 0.05). These results indicate that replacing HMC with NZ, considered an inert ingredient in diet formulation, did not influence dietary energy utilization under the conditions of this study. Additional evaluations, such as nutrient digestibility measurements, may be necessary to further clarify potential mechanisms by which NZ could affect energy metabolism. Overall, NZ supplementation did not improve the energetic value of high-concentrate diets fed to finishing Nellore bulls.