The performance, economic, and environmental consequences of feeding rumen degradable protein (RDP) levels above and below calculated maximum energy-dependent microbial crude protein (MCP) synthesis potential are poorly understood. Yearling steers (n = 54; initial BW = 484.1 ± 26.03 kg) were assigned to one of two pens that each contained an automated head chamber system (GreenFeed; C-Lock Inc., Rapid City, SD) for individual measurement of enteric methane (CH4) emissions. Each steer was assigned to an individual feed bunk (Calan Gate; American Calan, Northwood, NH) and randomly assigned to one of three dietary treatments: low RDP intake (LRDPI; n = 8), neutral RDP intake (NRDPI; n = 8), or high RDP intake (HRDPI; n = 8) in a completely randomized design. Steers were transitioned to treatment diets utilizing a two-ration blend system for 20-day followed by an 80-day finishing period. Diets were formulated to provide cattle with similar metabolizable protein (MP) and net energy for gain (NEg) but different RDP supply. Diets were formulated to provide approximately 87% (LRDPI), 100% (NRDPI), or 113% (HRDPI) of calculated RDP requirements to maximize energy-allowable MCP-yield. Paired-day, unshrunk BW was collected on d 0, 50, and 80, and cattle were transported to a commercial abattoir for carcass data collection. Statistical analyses were conducted using Analysis of Variance in JMP Pro6.0 using the Fit Model procedure. Least-squares means differences were considered statistically significant if P < 0.05 and considered a tendency toward significant if 0.05 ≤ P < 0.15. Treatment rations provided approximately 94% (LRDPI), 106% (NRDPI), and 118% (HRDPI) of the RDP required to maximize energy-allowable MCP yield, respectively. Daily DMI was similar (P > 0.15) for HRDPI and NRDPI cattle, but LRDPI cattle tended (P = 0.06) to have less DMI than NRDPI cattle. Dietary treatment did not affect (P ≥ 0.32) ADG, feed conversion efficiency, ribeye area, marbling score or carcass yield grade. Yet, LRDPI cattle had lighter hot carcass weight (P < 0.05) and less subcutaneous fat thickness (P < 0.05) than NRDPI cattle, whereas HRDPI cattle were not different (P ≥ 0.15) from the other treatments. On average, LRDPI cattle tended to emit 7.0% more daily CH4 (g×d-1; P = 0.05) than both NRDPI and HRDPI. Moreover, the LRDPI treatment elicited a 14.7% and 18.1% increase in CH4-yield (g CH4×kg DMI-1; P < 0.01) and emission intensity (g CH4×kg ADG-1; P < 0.05) compared with the other treatments, respectively. These data indicate that limiting MCP-yield by restricting RDP intake may reduce subcutaneous fat thickness and carcass weight while increasing enteric CH4 emissions. These results reiterate the importance of meeting RDP requirements and suggest no performance or methane emission benefits of overfeeding RDP.

Methane (CH4) is a greenhouse gas associated with global warming that is released as a byproduct of rumen fermentation. Two experiments were conducted to determine if dietary inclusion of a novel high anthocyanin (Hi-A) containing corn cob meal [CCM; 4.99 mg anthocyanin×g-1 of dry matter (DM)] influences in vitro CH4 emissions relative to a conventional CCM (CNV; 0.04 mg anthocyanin×g-1 of DM). High-roughage starter (experiment 1) and low-roughage finisher (experiment 2) diets were formulated to contain 20% and0% total CCM (DM-basis), respectively. Treatments were based on the proportion of Hi-A to CNV CCM within each diet and consisted of 0% (0A), 25% (25A), 50% (50A), 75% (75A), and 100% Hi-A (100A) CCM. In experiments 1 and 2, ruminal fluid was collected from 4 cannulated steers offered traditional feedlot starter or finisher diets, respectively. Filter bags (F57; ANKOM; Macedon, NY) were loaded with 0.5 g of substrate and 2 bags per ANKOM RF system were incubated in buffer and rumen fluid for 48 h at 39°C. Cumulative gas production was recorded at 10-min intervals. The concentration of CH4 as a proportion of total gas production (%CH4) was measured using gas chromatography after 48 h. Total gas production was fit to the Ørskov model to determine asymptotic and fractional rates of gas production. In experiment 1, there was a cubic relationship between total gas production and Hi-A CCM inclusion for the intercept, asymptote, and fractional gas production rate (P ≤ 0.04). There was also a cubic relationship between %CH4 and Hi-A CCM inclusion (P = 0.04), where 50A had the largest reduction relative to 0A at -19.6% (P = 0.05). Total CH4 production (mL CH4×g DM-1) also exhibited a cubic relationship with Hi-A-CCM inclusion (P = 0.03), where 100A produced 20% less CH4 than 0A. In experiment 2, there was a cubic relationship between total gas production and Hi-A CCM inclusion for the intercept and asymptote (P ≤ 0.02) of the Ørskov model; however, fractional gas production rate expressed a quadratic relationship (P < 0.01). Furthermore, a cubic relationship existed between %CH4 and Hi-A CCM inclusion, where 100A had the largest reduction relative to 0A (17.4%; P = 0.03). Lastly, there was a tendency for a cubic relationship between Hi-A CCM inclusion and total CH4 production (P = 0.06); however, 100A reduced total CH4 production by 22% relative to 0A (P = 0.01). Collectively, the greatest level of Hi-A CCM inclusion reduced total CH4 production relative to 0A in both starter and finisher diets. These results indicate that dietary inclusion of anthocyanins through CCM decreased CH4 emissions in vitro. Further research is needed to determine if anthocyanins from Hi-A CCM are effective at mitigating CH4 emissions in vivo.

Monensin is an ionophore commonly fed to feedlot cattle to increase feed efficiency (gain:feed ratio; G:F) typically by decreasing dry matter intake (DMI) when fed at the commonly adopted dose of 33 mg∙kg DM-1. During the receiving period when intake is often suppressed due to management stressors, feeding monensin to light-weight feedlot calves may be detrimental to DMI and consequently to growth performance. The objective of this experiment was to evaluate the effects of feeding sodium monensin to newly-received feedlot calves. A total of 380 crossbred beef steers [initial body weight (BW) = 231 ± 25 kg and approximately 8 months of age] were sourced from local auctions in Delhi, LA and transported approximately 16 h to Clayton, NM. Upon arrival, steers were processed, blocked by off-truck shrunk BW, randomly assigned to 20 pens (19 animal∙pen-1), and pens were then randomly assigned to one of two dietary treatments (n = 10 pens/treatment): control (CON; no feed additive) or sodium monensin at 170 mg∙animal-1∙day-1 (MON; Rumensin 90; Elanco Animal Health, Greenfield, IN). The basal diet consisted of a complete starter feed composed predominantly of wet corn gluten feed (RAMP; Cargill Sweet Bran, Dalhart, TX). The experiment was 56 days in length. The amount of feed offered to each pen was adjusted based on the DMI of the previous day and bunks were managed to contain trace amounts of feed at 0600 h. Body weight was recorded on days 0, 14, 28, and 56 for average daily gain (ADG) and G:F calculation. Dietary net energy for maintenance (NEm) and gain (NEg) were estimated based on observed growth performance. Daily animal health evaluations were performed using a 4-point scale method based on depression, appetite, respiration, and temperature throughout the experiment. All data were analyzed as a randomized complete block design using SAS with pen serving as the experimental unit. Feeding MON did not affect feed intake (P = 0.58) compared with CON, yet ADG was increased (P < 0.01) by 12.5% in steers fed MON compared with CON. Thus, there was a 10.7% increase (P < 0.01) in G:F for MON, which corresponds with a greater (P = 0.02) observed NEm and NEg for MON compared with CON. Feeding MON tended (P = 0.07) to elicit a 2.9% increase in final BW compared with CON. Additionally, there was no treatment effect (P ≥ 0.57) on morbidity based on the number of therapeutic treatments among calves which were treated for indications of bovine respiratory disease. Moreover, treatments did not affect mortality rate. In summary, feeding monensin at 170 mg∙animal-1∙d-1 (26 mg∙kg DM-1) increases growth performance of light-weight, newly-received feedlot cattle without influencing DMI or animal health.