Methane emissions and 13C composition from beef steers consuming binary C3-C4 diets

Authors: Jaramillo, David; RUIZ-MORENO, MARTIN - University Of Florida; VENDRAMINI, JOAO - University Of Florida; SOLLENBERGER, LYNN - University Of Florida; DILORENZO, NICOLAS - University Of Florida; DANTAS QUEIROZ, LUANA - University Of Florida; SANTOS, ERICK - University Of Alberta; GARCIA, LIZA - University Of Florida; ABREU, DACIELE - University Of Florida; DUBEUX, JOSE - University Of Florida

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2023
Publication Date: 6/2/2023
Citation: Jaramillo, D.M., Ruiz-Moreno, M., Vendramini, J., Sollenberger, L., Dilorenzo, N., Dantas Queiroz, L., Santos, E., Garcia, L., Abreu, D., Dubeux, J. 2023. Methane emissions and 13C composition from beef steers consuming binary C3-C4 diets. Journal of Animal Science. https://doi.org/10.1093/jas/skad181.
DOI: https://doi.org/10.1093/jas/skad181

Interpretive Summary: Investigating methods for reducing enteric methane emissions from ruminant livestock are important to reduce environmental impacts and improving production efficiency through reduced energy losses. This experiment evaluated the effects of increasing the proportion of rhizoma peanut hay (a C3 legume) into bahiagrass hay (a C4 grass) on intake, methane production, and methane carbon stable isotope composition in beef steers. Angus-crossbred steers were randomly allocated to one of five hay diets (treatments): 1) 100% bahiagrass; 2) 25% rhizoma peanut + 75% bahiagrass; 3) 50% rhizoma peanut + 50% bahiagrass; 4) 75% rhizoma peanut + 25% bahiagrass; 5) 100% rhizoma peanut. Inclusion of rhizoma peanut did not affect intake or methane production, but apparent total tract digestibility increased as proportion of rhizoma peanut increased in the diet. The carbon stable isotope composition observed from enteric methane production was within the expected ranges for C3-C4 forage diets. Furthermore, the carbon stable isotope composition from enteric methane production was useful in predicting contributions from each diet source in C3-C4 binary diets.

Technical Abstract: Improvements in forage nutritive value can reduce methane (CH4) emission intensity in grazing ruminants. This study was designed to evaluate how the legume rhizoma peanut (Arachis glabrata; RP) inclusion into bahiagrass (Paspalum notatum) hay diets would affect intake and CH4 production in beef steers. We also assessed the potential to estimate the proportion of RP contribution to CH4 emissions using d13C from enteric CH4. Twenty-five Angus-crossbred steers were randomly allocated to one of five treatments (5 steers per treatment): 1) 100% bahiagrass hay (0%RP); 2) 25% RP hay + 75% bahiagrass hay (25%RP); 3) 50% RP hay + 50% bahiagrass hay (50%RP); 4) 75% RP hay + 25% bahiagrass hay (75%RP); 5) 100% RP hay (100%RP). The study was laid out using a randomized complete block design, and the statistical model included the fixed effect of treatment, and the random effect of block. Methane emissions were collected using sulfur hexafluoride (SF6) technique, and apparent total tract digestibility was estimated utilizing indigestible NDF (iNDF) as an internal marker. A two-pool mixing model was used to predict diet source utilizing CH4 d13C. Inclusion of RP did not affect intake or CH4 production (P > 0.05). Methane production per animal averaged 250 g CH4/ d and 33 g CH4/kg DMI, across treatments. The CH4 d13C values were -55.5, -60.3, -63.25, -63.35, and -68.7 for 0%RP, 25%RP, 50%RP, 75%RP, and 100%RP respectively, which are within the accepted ranges for C3 or C4 forage diets. Moreover, there was a quadratic effect (P = 0.04) on the CH4 d13C, as the diet proportion of RP hay increased. Regression between predicted and observed proportions of RP in bahiagrass hay diets based on d13C from CH4 indicate d13C is useful (Adj. R2 = 0.89) for predicting the contribution of RP in C3-C4 binary diets. Data from this study suggest that CH4 production may not always be reduced with legume inclusion into C4 hay diets. However, there is potential to estimate CH4 production contribution from individual diet components in ruminants consuming binary C3-C4 diets.