Evaluation of the Effect of Intake on Methane Production in Growing Cattle Fed Forage-Based Diets

Crossbred steers (n=80; initial BW = 274 kg, SD = 21) were used to evaluate the effect of DMI on CH₄ production in growing steers. Two treatments with 4 pens per treatment (10 steers/pen) were used in a generalized randomized block designed experiment using 4 blocks based on BW. The treatments included feeding the same diet either ad-libitum or limit-fed. Diets consisted of 45% alfalfa, 30% sorghum silage, 22% modified distillers grains plus solubles and supplement at 3% on a DM basis. The limit-fed cattle were fed 75% of the ad-lib cattle intake from the previous week from their corresponding paired pen. Methane measurements were performed on cattle using pen-scale methane chambers within each block so that both treatments (ab-libitum and limit-fed) could be measured at the same time. The steers were limit fed for 5 d at the beginning and end of the trial and weighed on two consecutive days to equalize gut fill for accurate initial and ending BW measurements. Steers were fed treatments for 105 d and emissions data were collected for 3, 5 consecutive d periods. The results presented are only from one rotation (3^rd collection) through the barn due to sensor errors for methane data collection in the first 2 periods. Steers fed ad-libitum had greater ending BW, DMI, and ADG (P < 0.01) compared to limit-fed cattle; however, G:F was not different between treatments (P = 0.33) because DMI was 26.2% greater and ADG was 23.3% greater for ad-libitum cattle compared to limit-fed cattle. Cattle fed ad-libitum eructated 156 g/d which was greater (P < 0.01) than limit-fed cattle (126 g/steer daily). When adjusted to an equivalent DMI basis, limit-fed steers tended to produce more CH₄ (P = 0.06) than ad-libitum fed steers. No difference was observed when expressing CH₄ per unit of ADG (P = 0.46) between ad-libitum and limit-fed treatments. Cattle fed ad-libitum produced more CO₂ (P = 0.04) per day compared to limit-fed cattle, but produced more (P = 0.02) CO₂ per unit of DMI. These data are consistent with previous work, illustrating that level of intake affects daily amounts of methane production but lower intakes result in slightly greater amounts of methane per unit of intake.