Enteric and fecal methane emissions from dairy cows fed grass or corn silage diets supplemented with rapeseed oil

Abstract

This study evaluated potential trade-offs between enteric methane (CH4) emissions and CH4 emissions from feces of dairy cows fed grass silage or partial replacement of grass silage with corn silage, both with and without supplementation with rapeseed oil. Measured data for eight dairy cows (two blocks) included in a production trial were analyzed. The cows were assigned to a 4 x 4 Latin square design, with a 2 x 2 factorial arrangement of dietary treatments and 28-d periods. Dietary treatments were: grass silage (GS), GS supplemented with rapeseed oil (GS-RSO), GS plus corn silage (GSCS), and GSCS supplemented with rapeseed oil (GSCS-RSO). Enteric CH4 emissions were measured by the GreenFeed system. Data from the last 10 days of each period were used for CH4 and for feed intake. Feces samples were collected after each period and incubated for 9 weeks to estimate fecal CH4 emissions. Including RSO in the diet decreased dry matter intake (DMI) by 1.75 kg/d, while partial replacement of grass silage by corn silage tended to reduce DMI by 1.2 kg/d. Enteric CH4 emissions were reduced by inclusion of RSO in the diet (on average 473 vs. 607 L/d). Microbial analysis showed no differences in Archaea abundance in cow feces, regardless of forage type or RSO supplementation. In 9-week incubations, there was a trend for lower CH4 emissions from feces of cows fed diets supplemented with RSO (on average 3.45 L/kg DM) than cows with diets not supplemented with RSO (3.84 L/kg DM). However, fecal total CH4 emissions (L/d) did not differ between the diets. Total CH4 emissions (enteric + feces, L/d) were significantly lower for the cows fed diets supplemented with RSO. Thus partial replacement of GS by CS supplemented with RSO reduced DMI, and consequently enteric CH4 emissions, in dairy cows. Total fecal CH4 emissions were similar between treatments, indicating no trade-offs between enteric and fecal CH4 emissions