Long-term supplementation of diets with 3-nitrooxypropanol resulted in a sustained reduction in methane production in beef cattle
The objective was to evaluate whether long-term supplementation of diets with 3-nitrooxypropanol (NOP), a synthetic compound proven to reduce enteric CH4 emissions in short-term studies, results in a sustained reduction in enteric CH4 emissions in beef cattle. Eight ruminally cannulated heifers (637 ± 16.2 kg of BW) were used in a completely randomized design with 2 treatments: Control (0 g/d of NOP) and NOP (2 g/d of NOP). Treatments were mixed by hand into the TMR (60% forage, DM basis) at feeding time. Feed offered was restricted to 65% of ad libitum DM intake (DMI; maintenance energy intake) to avoid excessive growth. Duration of the experiment was 146 d, including an initial covariate period without NOP supplementation (18 d), 4 periods with NOP supplementation (28 d each), and a final recovery period without NOP supplementation (16 d). Methane was measured at the end of each period for 3 d using metabolic chambers. Volatile fatty acid (VFA) concentration and microbial populations were measured using rumen samples collected 0, 3 and 6 h after feeding. Data were analysed using the PROC MIXED procedure of SAS. Average DMI for the experiment was 7.0 ± 0.2 kg. Methane intensity was reduced by 60% when NOP was supplemented (22.6 vs 8.9 g/kg DMI; P < 0.01) with no signs of adaptation (period × treatment, P = 0.2). Total VFA concentrations were not affected (P = 0.12); however, acetate concentration was reduced and propionate concentration increased when NOP was supplemented (P < 0.01), which led to a reduction in the acetate to propionate ratio (3.9 vs 2.9; P < 0.01). NOP had no effect on the copy number of the 16S rRNA gene of total bacteria (P = 0.5) but the copy numbers of the 16S rRNA gene of methanogens (P < 0.01) were reduced and copy numbers of the 18S rRNA gene of protozoa (P = 0.03) were increased. All effects of NOP observed during the measurement periods were absent during the recovery period when supplementation was discontinued. These results showed that reduction of CH4 production in ruminants is sustained with long-term dietary supplementation of NOP.
Keywords: 3-nitrooxypropanol, beef cattle, methane