Effects of protein supplementation to steers consuming low-quality forages on greenhouse gas emissions

• Published in: Journal of animal science Vol. 99; no. 7
• Main Authors: Shreck, Adam L, Zeltwanger, Joshua M, Bailey, Eric A, Jennings, Jenny S, Meyer, Beverly E, Cole, Noel Andy
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 01.07.2021
• Subjects: Acetic acid; Beef cattle; Body weight; Carbon dioxide; Carbon dioxide emissions; Cattle; Circuits; Cottonseed meal; Dry matter; Emissions; Energy intake; Fermentation; Fluxes; Greenhouse gases; Metabolism; Methane; Propionic acid; Proteins; Ruminant Nutrition; Supplements; Urea; methane; cattle; low-quality forage; protein; Low-quality forage; Methane; Cattle; Protein
• ISSN: 0021-8812; 1525-3163
• DOI: 10.1093/jas/skab147

Providing supplements that enhance the efficiency of feed utilization can reduce methane (CH4) emissions from ruminants. Protein supplementation is widely used to increase intake and digestion of low-quality forages, yet little is known about its impact on CH4 emissions. British-cross steers (n = 23; initial body weight [BW] = 344 ± 33.9 kg) were used in a three-period crossover design to evaluate the effect of protein supplementation to beef cattle consuming low-quality forage on ruminal CH4, metabolic carbon dioxide (CO2) emissions, forage intake, and ruminal fermentation. Steers individually had ad libitum access to low-quality bluestem hay (4.6% crude protein [CP]) and were provided supplemental protein based on (dry matter basis): cottonseed meal (CSM; 0.29% of BW daily; 391 g/d CP), dried distillers grains with solubles (DDGS; 0.41% of BW daily 563 g/d CP), or none (CON). Urea was added to DDGS to match rumen degradable protein provided by CSM. Ruminal CH4 and metabolic CO2 fluxes were obtained 2.4 ± 0.4 times per steer daily using an automated open-circuit gas quantification system (GreenFeed emission monitoring system; C-Lock Inc., Rapid City, SD). Forage intake increased (P < 0.01) with protein supplementation; however, no difference in forage intake (P = 0.14) was observed between CSM and DDGS treatments. Flux of CO2 (g/d) was greater (P < 0.01) for steers fed CSM and DDGS than for steers fed CON. Steers supplemented with CSM had greater (P < 0.01) CH4 emissions (211 g/d) than DDGS (197 g/d) both of which were greater (P < 0.01) than CON (175 g/d). Methane emissions as a proportion of gross energy intake (GEI) were lowest (P < 0.01) for DDGS (7.66%), intermediate for CSM (8.46%) steers, and greatest for CON (10.53%). Steers fed DDGS also had the lowest (P < 0.01) ruminal acetate:propionate ratio (3.60), whereas CSM (4.89) was intermediate, and CON (5.64) steers were greatest. This study suggests that the common practice of supplementing protein to cattle consuming low-quality forage decreases greenhouse gas emissions per unit of GEI.