Shreck Adam L, Zeltwanger Joshua M, Bailey Eric A, Jennings Jenny S, Meyer Beverly E, Cole Noel Andy
Conservation and Production Research Laboratory, USDA-ARS, Bushland, TX, USA.
Division of Animal Sciences, University of Missouri, Columbia, MO, USA.
J Anim Sci. 2021 Jul 1;99(7). 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.
提供能提高饲料利用效率的补充剂可以减少反刍动物的甲烷（CH4）排放。蛋白质补充剂被广泛用于增加低质粗饲料的摄入量和消化率，但人们对其对CH4排放的影响知之甚少。本研究采用三头期交叉设计，选用英国杂交阉牛（n = 23；初始体重[BW] = 344 ± 33.9 kg），评估给采食低质粗饲料的肉牛补充蛋白质对瘤胃CH4、代谢二氧化碳（CO2）排放、粗饲料摄入量和瘤胃发酵的影响。阉牛单独自由采食低质须芒草干草（粗蛋白[CP]含量为4.6%），并根据（干物质基础）提供补充蛋白质：棉籽粕（CSM；每日体重的0.29%；391 g/d CP）、干酒糟及其可溶物（DDGS；每日体重的0.41%，563 g/d CP），或不补充（CON）。向DDGS中添加尿素以匹配CSM提供的瘤胃可降解蛋白。使用自动开路气体定量系统（GreenFeed排放监测系统；C-Lock Inc.，拉皮德城，南达科他州），每天对每头阉牛进行2.4 ± 0.4次瘤胃CH4和代谢CO2通量测定。补充蛋白质后粗饲料摄入量增加（P < 0.01）；然而，CSM和DDGS处理之间的粗饲料摄入量没有差异（P = 0.14）。采食CSM和DDGS的阉牛的CO2通量（g/d）高于采食CON的阉牛（P < 0.01）。补充CSM的阉牛的CH4排放量（211 g/d）高于DDGS（197 g/d）（P < 0.01），两者均高于CON（175 g/d）（P < 0.01）。作为总能摄入量（GEI）比例的甲烷排放量，DDGS最低（P < 0.01）（7.66%），CSM阉牛居中（8.46%），CON最高（10.53%）。采食DDGS的阉牛的瘤胃乙酸:丙酸比例也最低（P < 0.01）（3.60），CSM（4.89）居中，CON阉牛（5.64）最高。本研究表明，给采食低质粗饲料的牛补充蛋白质的常见做法可降低单位GEI的温室气体排放量。
