37. Effects of 3-nitrooxypropanol on Methane Emissions and Lactation Performance of Dairy Cows in Early Lactation.

Abstract Enteric methane emissions from dairy cattle constitute a substantial portion of agricultural greenhouse gases. The objective of this study was to evaluate the effects of 3-nitrooxypropanol (3-NOP) supplementation on lactation performance in dairy cows during the first 100 days of lactation. At the start of the dry period, 60 days prior to calving, cows were randomly assigned to one of three treatments: control (CON), 40 mg 3-NOP/kg DMI (40NOP), or 80 mg 3-NOP/kg DMI (80NOP). Daily emissions were measured using the GreenFeed system, while production parameters – dry matter intake (DMI), milk yield, body weight (BW), body condition score (BCS), and milk composition – were collected throughout this experiment. Data were analyzed in R (version 4.3.3) using liner mixed-effects models (lme4), with treatment, days in milk (DIM), and their interaction as fixed effects, cow as a random effect, and repeated measures over time accounted for within cow. Supplementation with 3-NOP had no effect on DMI (53.2, 52.1, and 50.9 kg/d for CON, 40NOP, and 80NOP respectively; P = 0.58), milk yield (44.7, 45.5, and 44.6 kg/d; P = 0.90), body weight (621, 627, and 628 kg; P = 0.93), body condition score (3.02, 3.13, and 3.05;P = 0.26), milk fat percentage (4.07, 3.87, and 4.08%; P = 0.44), milk protein percentage (3.02, 3.02, and 3.06%; P = 0.76), or energy corrected milk, ECM (48.1, 49.9, and 48.1 kg/d; P = 0.82). Methane production differed by treatment (P < 0.001) and averaged 436, 298, and 252 g/d for CON, 40NOP, and 80NOP, respectively, with reductions of 32% and 42% for 40NOP and 80NOP respectively. However, methane yield differed by treatment (P < 0.001) and was lower in 40NOP and 80NOP compared with CON averaging 9.49, 5.99, and 5.15 g/kg DMI for CON, 40NOP, and 80NOP, respectively: corresponding to reductions of 37% and 46%. Methane intensity per unit of ECM differed by treatment (P < 0.001), and averaged 4.68, 3.03, and 2.63 g/kg ECM for CON, 40NOP, and 80NOP, respectively. This study demonstrates that 3-NOP effectively reduces methane without negatively affecting DMI and performance parameters. Thus, 3-NOP can serve as an effective methane-mitigation strategy for reducing the environmental footprint of dairy production.