Effects of 3-nitrooxypropanol on methane emissions, rumen fermentation and performance of Hanwoo steers fed an early fattening stage diet.

3-nitrooxypropanol (3-NOP) has been recognized as an effective feed additive to reduce enteric methane (CH4) emissions in ruminants. The current experiment evaluated the effects of supplementation of Bovaer®10 (diluted preparation of 3-NOP, minimum 10% w/w) on enteric CH4 emissions in Hanwoo (Korean native cattle) steers. Twelve Hanwoo steers (average body weight 342 ± 17 kg) were divided into three groups of 4 steers balanced for body weight. Within each group, steers were randomly assigned to three dietary treatments in a crossover design, receiving each treatment in a different period of 32 days. The treatments were: (1) CON, 500 g/kg dry matter (DM) timothy hay and 500 g/kg DM commercial concentrate; (2) NOP100, CON diet supplemented with 100 mg of 3-NOP per kg dietary DM; (3) NOP150, CON diet supplemented with 150 mg of 3-NOP per kg dietary DM. Gas emissions (CH4 and carbon dioxide [CO2]) were measured using the whole-body respiratory chambers (RC). Compared to control, NOP100 and NOP150 decreased CH4 absolute emissions by 21.9% and 29.5% (p < 0.01), and CH4 yield (g/kg DM intake [DMI]) by 22.9% and 27.7% (p < 0.01), respectively. The proportion of gross energy intake lost as CH4 (Ym) decreased (p < 0.01) by 22.8% and 27.6% in NOP100 and NOP150, respectively. NOP150 diet slightly decreased DMI of the steers both in the barn (2.5%; p < 0.05) and in the RCs (3.3%; p = 0.06). However, no negative effect (p > 0.05) on final body weight, average daily gain or gain to feed ratio was observed. Increased (p < 0.05) ruminal pH and decreased total volatile fatty acid and ammonia concentration was noted in 3-NOP fed animals in a dose-dependent manner after 2 h of feeding. The increase (p < 0.01) in molar proportions of butyrate and propionate and decrease (p < 0.01) in acetate: propionate ratio, respectively, clearly reflected a shift in the ruminal H2 sink in 3-NOP fed animals. Overall, supplementing 3-NOP to ruminant diets decreased CH4 emissions without any adverse effects on performance of Hanwoo steers at the tested levels.