Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 27, 2013
Publication Date: September 27, 2013
Citation: Freetly, H.C., Brown-Brandl, T.M. 2013. Enteric methane production from beef cattle that vary in feed efficiency. Journal of Animal Science. 91(10):4826-4831. Interpretive Summary: Methane gas released by cattle is a product of fermentation in the digestive tract. Released methane represents both a lost opportunity to capture dietary energy and a source of greenhouse gas. Two experiments were conducted to determine the relationship between the efficiency of feed utilization for body weight gain, and the amount of methane produced per unit feed consumed. On a high-forage diet, methane emissions increased with increased feed efficiency. There was not a relationship between methane production and feed efficiency on a high-grain diet. Our findings suggest that selecting only for reduced methane may have a negative impact on conversion of feed to body tissues.
Technical Abstract: We hypothesized that CH4 production will decrease with increased feed efficiency. Two experiments were conducted to determine CH4 production of cattle that differed in feed efficiency. Cattle in both studies were selected from larger contemporary groups. Animals furthest from the confidence ellipse that resulted from regressing BW gain on DMI were selected. In the first experiment, 113 crossbred steers were evaluated for feed efficiency for 64 d. Steers were 355 ± 1 d of age and weighed 456 ± 10 kg when they began the study. Steers were fed a ration that consisted of (dry matter basis) 82.8% corn, 12.8% corn silage, and 4.5% supplement (contains 0.065% monensin, 32% CP (28% NPN), 7.5% Ca, 0.8% P, 4.8% NaCl 1.8% K, and 55,116 IU/kg Vitamin A). Thirty-seven steers were selected to measure CH4 production. In the second experiment, 197 heifers were evaluated for feed efficiency for 64 d. Heifers were 286 ± 1 d of age and weighed 327 ± 2 kg when they began the study. Heifers were fed a ration that consisted of (dry matter basis) 60% corn silage, 30% alfalfa hay, and 10% wet distillers grains with solubles. Forty-seven heifers were selected to measure CH4 production. Methane production was measured with respiration calorimeters. In both experiments, cattle had ad libitum access to feed, and DMI consumed during the 24 h before CH4 production was measured. Methane production was collected for a 6-h period on untrained cattle; consequently, methane production is not a quantitative measure of daily methane production rather it is an index value to rank cattle. Multiple regression analysis was used to determine the relationship between either BW gain:DMI ratio or residual feed intake (RFI) on CH4 production after adjusting for the previous 24 h DMI. In the steers, gain:DMI ratio and previous 24 h feed intake accounted for little of the variance in CH4 production (R2 = 0.009), nor did RFI and previous 24 h feed intake (R2 = 0.001). In the heifers, the gain:DMI ratio contributed 28% toward the variance estimate and previous 24-h DMI contributed 72% toward the variance estimate (R2 = 0.31). As the gain:DMI ratio increased daily CH4 production increased. The regression coefficient for RFI (P = 0.45) did not differ from zero for CH4 production. Our study does not support our original hypothesis that CH4 production decreases with increased feed efficiency, and suggests that CH4 production may increase with increased feed efficiency.