339. Influence of Cashew Nutshell Extract on Enteric Methane Emissions, Ruminal Fermentation, and Animal Performance of Finishing Natural Heifers.

Abstract Enteric methane (CH4) from feedlot cattle is both a greenhouse gas and an energetic loss, diverting 2 to 12% of dietary gross energy (GE). Cashew processing produces large quantities of waste, some of which can be refined into cashew nut shell extract (CNSE), a phenolic-rich supplement containing anacardic acid. This study evaluated effects of CNSE supplementation on methane emissions, animal performance, feeding behavior, and carcass characteristics in finishing heifers. Sixty crossbred heifers (initial body weight = 515 ± 9 kg) were assigned to 1 of 4 treatments (n = 15/treatment): 0, 2.5, 5.0, or 7.5 g CNSE/heifer daily for 105 d. The CNSE (DynOmik, Adisseo, Alpharetta, GA) contained at least 25% anacardic acid. The finishing diet contained (DM basis) 23% corn silage, 20% distillers' grains, 55% corn, and 3% vitamin/mineral supplement. Intake and feeding behavior were recorded using an Insentec Roughage Intake Control (RIC) system (Hokofarm, Emmeloord, The Netherlands). CH4 emissions were measured using an automated head chamber system (AHCS; GreenFeed; C-Lock Inc., Rapid City, SD). Relative to control, supplementation with 2.5 g/d CNSE increased dry matter intake (DMI) (12.64 vs. 11.86 kg/d), whereas supplementation of 5.0 (11.00 kg/d) and 7.5 g CNSE/d (10.72 kg/d) reduced DMI (cubic P = 0.005). Average daily gain (ADG) decreased linearly (P = 0.02) as CNSE inclusion increased (1.31, 1.34, 1.17, and 1.17 kg/d for 0, 2.5, 5.0, and 7.5 g CNSE/d). Gain:feed ratio was not affected by treatment (P ≥ 0.33). Methane production (g/d) was not different among treatments (P ≥ 0.26). Methane yield (g/kg DMI) and methane conversion factor (Ym, % of GE intake lost as methane) showed cubic tendencies, with lower values at 2.5 g/d than at 0, 5.0, and 7.5 g/d (14.2 vs. 15.8, 16.2, and 16.3 g/kg DMI; and 4.60 vs. 5.14, 5.30, and 5.33%; cubic P = 0.095 and 0.077), whereas methane intensity (g/kg ADG) was not affected by CNSE supplementation (P ≥ 0.09). Heifers supplemented with 2.5 g CNSE/d had greater meal size (1.85 kg/meal), whereas meals per day increased with CNSE inclusion (linear P = 0.03) and eating rate decreased as CNSE inclusion increased (linear P = 0.03). Carcass characteristics, including fat thickness, ribeye area, hot carcass weight, marbling score, and calculated yield grade were not affected by treatment (P ≥ 0.49). Prime and choice percentages showed quadratic tendencies, with lower prime and greater choice percentages at 2.5 and 5.0 g/d CNSE than at 0 and 7.5 g/d (P = 0.06 and 0.07). Supplementation with CNSE altered feeding behavior and reduced growth performance at 5.0 and 7.5 g CNSE/d. Absolute methane production was not affected by CNSE, although methane yield and Ym showed cubic tendencies suggesting a reduction in CH4 at 2.5 g CNSE/d.