Daily methane production pattern of Welsh ponies fed a roughage diet with or without a cereal mixture 1

Methane production from Welsh ponies fed 2 isoenergetic diets (NE basis) at maintenance was studied in a crossover design with 4 mature geldings (230 ± 10.5 kg BW, mean ± SE). Treatments included a roughage-only (R) diet (5.1 kg DM/d) or a roughage plus cereal mix (RC) diet (2.5 kg DM hay/d plus 1.1 kg DM cereal mix/d). For both diets, the same grass hay was used (898 g DM/kg and 4.5 MJ NEm/kg DM) and a commercial cereal mix was used in the RC diet (890 g DM/kg and 9.6 MJ NEm/kg DM). Ponies were housed in pairs in climate-controlled respiration chambers. Carbon dioxide production (CO^sub 2^), oxygen (O^sub 2^) consumption, and CH^sub 4^ production were measured over 3 consecutive days. Heat production (HP) rates were calculated from gaseous exchange. Feces were collected quantitatively to determine dietary nutrient digestibility. Dry matter intake differed between diets (P < 0.0001), but NE intake was equal for both diets (22.3 ± 0.07 MJ NEm/d). Organic matter digestibility was lower (P = 0.006) for the R diet (47.2%) than the RC diet (55.6%). Methane production was higher (P = 0.014) on the R diet (29.8 L.pony^sup -1^.d^sup -1^) compared to the RC diet (23.2 L.pony^sup -1^.d^sup -1^). Methane production expressed in liters/kilogram metabolic body weight (BW^sup 0.75^) per day tended (P = 0.064) to decrease with 21% for the RC group compared with the R group. Heat production, O^sub 2^ consumption, and CO^sub 2^ production were not affected by diet. Diurnal patterns of CH^sub 4^ production and HP were similar for both diets. Methane production increased slightly (P < 0.652) after feeding and was numerically lower for the RC diet for all time points throughout the day. For both diets, HP was higher after feeding than before feeding and decreased again within approximately 3 h after feeding. Isoenergetic replacement of roughage by a cereal mix reduces CH^sub 4^production in ponies. No clear diurnal pattern in CH^sub 4^ emission can be discerned in ponies fed at maintenance.