Hourly methane production in finishing steers fed at different levels of dry matter intake

Methane (CH₄) loss from finishing cattle is important as it represents an energy loss that could be used for maintenance and growth, and CH₄ is a greenhouse gas with a global warming potential 21 to 25 times that of CO₂. Our objectives were to determine hourly CH₄ production from growing cattle fed diets differing in corn processing method (dry rolling or steam flaking) and wet distillers grains with solubles (WDGS) inclusion rate. Eight steers (195 kg ± 2.3 in Exp. 1 and 322 kg ± 3.7 in Exp. 2) were fed the following diets: 1) steam-flaked corn (SFC)-based diet with 0% WDGS (SFC-0); 2) SFC-based diet with 15% WDGS (SFC-15); 3) SFC-based diet with 30% WDGS (SFC-30); 4) SFC-based diet with 45% WDGS (SFC-45); 5) Dry-rolled corn (DRC)-based diet with 0% WDGS (DRC-0); and 6) DRC-based diet with 30% WDGS (DRC-30). All hourly CH₄ data were analyzed using the MIXED procedure of SAS. Individual animal was the experimental unit. The model included the fixed effect of h, diet, and the h × diet interaction. Hourly differences in CH₄ were analyzed using repeated measures. There were numerous h × diet interactions and thus simple-effect means are presented. In steers fed DRC-0 or DRC-30 at 2-times maintenance, the greatest hourly CH₄ emissions occur 6 h after feeding (P < 0.01) with a secondary peak between 10 and 11 h after feeding (P < 0.01). For cattle fed SFC-0, SFC-15, SFC-30, and SFC-45 at 2-times maintenance, all diets had peak CH₄ emissions 5 and 6 h after feeding (P < 0.01), with a secondary CH₄ peak for SFC-45 nine to 11 h after feeding (P < 0.01). Cattle fed all diets at a maintenance level of intake exhibited 1 peak in hourly CH₄ production between 3 and 6 h after feeding (P < 0.01). All steers fed SFC-30 and SFC-45 had sustained CH₄ production over several hours, irrespective of intake level. Steers fed SFC-45 produced more CH₄ beginning 4 h after feeding (P < 0.01) and produced a greater amount of CH₄ than any other treatment (P < 0.01). Methane production generally peaked 6 h after feeding irrespective of intake level or diet type. Additionally, when fed above a maintenance level of intake, a secondary peak in CH₄ production was observed 9 to 11 h after feeding, and steers fed at a maintenance level of intake had only 1 peak in CH₄ production in a 23-h period.