There is an urgent requirement internationally to reduce enteric methane (CH4) emissions from ruminants to meet greenhouse gas emissions reduction targets. Dietary supplementation with feed additives is one possible strategy under investigation as an effective solution. The effects of the CH4inhibitor 3-nitrooxypropanol (3-NOP) at reducing CH4emissions in beef have been shown mainly in adult cattle consuming backgrounding and high-energy finishing diets. In this study, the effects of dietary supplementation of young growing (≤6 mo) beef cattle with 3-NOP were examined in a 50:50 forage:concentrate diet. A total of 68 Dairy × Beef (Aberdeen Angus and Hereford dairy cross) male calves (≤6 mo of age at the start of experiment, body weight: 147 ± 38 kg) underwent a 3-wk acclimatization period and were then assigned to one of two treatments in a completely randomized block design. Dietary treatments were (1) control, placebo (no 3-NOP), and (2) 3-NOP applied at 150 mg kg−1DM. Calves were fed a partial mixed ration for 12 wk. Body weight was recorded weekly and feed intake daily using the Calan Broadbent feeding system. Methane and hydrogen emissions were measured using the GreenFeed system. Total weight gained, dry matter intake (DMI), and average daily gain were not affected by 3-NOP (P> 0.05) supplementation. On average, the inclusion of 3-NOP decreased (P< 0.001) CH4emissions: g d−1; g kg−1DMI; by 30.6% and 27.2%, respectively, during the study with a greater reduction occurring over time. Incorporating 3-NOP into beef cattle diets is an efficient solution to decrease CH4emissions during indoor feeding and when offered 50:50 forage:concentrate diet.This research highlights the efficacy of the methane (CH4) inhibitor, 3-nitrooxypropanol, in reducing CH4emissions in young growing beef cattle without affecting dry matter intake and animal performance when consuming a 50:50 forage:concentrate diet.Enteric methane (CH4) is a by-product from the fermentation of feed in the digestive tract of cattle. The production of CH4is responsible for the loss of 2% to 12% of the animal’s gross energy intake. A potent greenhouse gas, CH4from ruminant systems accounts for 30% of international anthropogenic CH4emissions. As a result, a significant effort has been made internationally to reduce CH4emissions from ruminants in order to achieve reductions in global greenhouse gas emissions. The supplementation of additives in the feed has been demonstrated to be an effective strategy in reducing CH4emitted from livestock. The purpose of this research was to investigate the effects of supplementing young growing cattle with the CH4inhibitor, 3-nitrooxypropanol (3-NOP), consuming a 50:50 forage:concentrate diet. A total of 68 Dairy × Beef (Aberdeen Angus and Hereford dairy cross) male calves (≤6 mo of age at the start of the experiment) were assigned to one of two treatments: control (no 3-NOP) and 3-NOP. Animals received their diets for 12 wk. Animal performance was recorded weekly, with CH4and hydrogen (H2) emissions recorded daily. Dry matter intake and animal performance were not affected by the inclusion of 3-NOP. Over the duration of this study, the inclusion of 3-NOP decreased daily CH4emissions by 30.6%, with a 227% increase in daily H2emissions.