Long-term supplementation of diets with 3-nitrooxypropanol resulted in a sustained reduction in methane production in beef cattle

Abstract Text:

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