358 Late-Breaking: Growth performance and enteric gas emissions in grazing beef heifers fed Agolin®

Abstract A grazing trial was conducted to evaluate the growth performance and enteric gas emissions of beef heifers effects of fed a plant-derived essential oil supplement (Agolin®). For this study, 63 crossbred beef heifers were used (BW = 274 ± 42 kg) and grazed a 24-hectare triticale (Triticosecale spp.) pasture near Minneola, Kansas. Heifers were stratified based on BW and pre-trial AHCS (Automated Head Chamber System) acclimation rates into one of two supplementation treatments: 1) AGO: Agolin® with dry distillers grain at 0.5 kg/d, or 2) CON: dry distillers grain at 0.5 kg/d. The primary objectives were to assess differences in enteric methane (CH₄) and carbon dioxide (CO₂) emissions, and average daily gain (ADG) with and without Agolin® supplementation. Body weights were recorded at the start (day 0), midpoint (day 35), and conclusion of the 78-day grazing period. Enteric emissions were measured using a GreenFeed emission measurement system (AHCS; C-Lock Inc., Rapid City, SD). Supplement treatments were offered using SmartFeed Pro units (C-Lock Inc., Rapid City, SD) to allow individual-heifer access and consumption while enabling comingling of treatments in one experimental pasture. Only animals with ≥20 SmartFeed Pro visits (and an average supplement intake ≥0.25 kg/day) over the trial were selected to represent consistent supplement users (n = 28). Statistical analyses were conducted in R (version 4.4.1). General linear models were used to assess differences between treatments for ADG (kg/d), CH4 (g/d), CO2 (g/d) and emission intensity (g CH4 per kg ADG) with potential influential points identified using Cook’s distance model. ADG did not differ significantly between AGO (0.69 kg/d) and CON (0.62 kg/d) cattle (P = 0.18), although numerically higher ADG was observed in the AGO group. Enteric CH4 production was lower (P = 0.05) for AGO (162 g/d) compared to CON (178 g/d), while CO2 did not differ (P = 0.15) between treatments, but numeric differences were observed (6,120 g/d AGO vs 6,507 g/d CON). The numeric differences in performance and lower enteric CH4 emissions are reflected in the emission intensity results. AGO cattle demonstrated lower (P = 0.03) emissions intensity (243 g CH4/kg ADG) compared to CON cattle (293 g CH4/kg ADG). These findings suggest beneficial modulation of enteric emissions with Agolin, but further studies with larger sample sizes and optimal supplement intake are needed to confirm efficacy under grazing conditions.