Isoacid supplementation influences feed sorting, chewing behaviors, and enteric methane emissions differentially in mid-lactation dairy cows depending on dietary forage level

Past studies have shown that isoacids (ISO) improve dairy cow performance, with effects varying based on dietary forage levels, leading us to speculate that ISO supplementation may also differentially affect enteric methane (CH4) emissions depending on dietary forage levels. Therefore, our primary objective was to examine the effects of ISO supplementation on enteric CH4 emissions in lactating dairy cows fed 2 forage NDF levels (FL), along with monitoring feed particle sorting and chewing behaviors to assess any potential interactions. a 10-wk long randomized complete block design trial. Parity, DIM, and prior milk yield (MY) for multiparous cows or genetic merit for primiparous cows were used as blocking factors. Cows were randomly assigned to 1 of 4 diets (n = 16 per diet) with a 2 x 2 factorial arrangement of treatment combinations, including 2 FL, 17% (LF) and tation (7.85 mmol/kg DM for isobutyrate and 3.44 mmol/ and chewing activity (rumination and eating time) were measured using the GreenFeed system and sensor-based in HF (100.8 vs. 92.5; P = 0.04). In contrast, ISO did not affect the physically effective particle sorting index (P = 0.51) or intake (P = 0.27) regardless of FL. In alignment with the long particle sorting index, ISO decreased eating and chewing time in the HF but increased them in the LF diet (P < 0.01). In contrast, rumination time was comparable between FL (P = 0.70) and ISO levels (P = 0.19). In the LF diet, ISO supplementation reduced daily CH4 production (g/d) by 9% and intensity (g/kg of MY) by 18% (P < 0.01). In the HF diet, ISO supplementation led to a 10% increase in daily CH4 (P < 0.01) but did not change CH4 intensity (P = 0.17; g/kg of MY) due to improved milk production. Overall, ISO altered feed sorting, feeding behaviors and enteric CH4 emissions depending on FL.