Feedlot efficiency implications on greenhouse gas sustainability

Abstract

ABSTRACT The term sustainable has many meanings,but in agriculture it generally refers to somebalance between environmental, social, and economicgoals. The objective of this project was to quantify inputsand outputs to assess the sustainability implicationsof 2 feedlot cattle management systems: NeverEver 3 (NE3) and a conventional (CON) system usingmetabolic modifiers. Angus-cross steers (n = 104) werestratified by BW (337 kg ± 17) and randomly assignedto 4 pens per treatment group. The NE3 cattle receivedno feed additives or implants, whereas CON were implantedwith 100 mg of trenbolone acetate and 14 mg ofestradiol benzoate on d 1 and 70, and were additionallyfed monensin [330 mg/(animal·d)] and tylosin phosphate[90 mg/(animal·d)] in their ration throughoutthe course of the study, and ractopamine hydrochlorideat 254 mg/(animal·d) for the last 29 d on feed. Cattlewere shipped on a constant average pen weight basis(596 kg ± 32 BW). The CON cattle had greater ADG(1.81 vs. 1.35 kg, P < 0.01) and were on feed fewer days(146 vs. 188 d, P < 0.01) than the NE3 cattle. No significantdifferences were observed in HCW (P = 0.072)or dressing percentage (P = 0.62) between treatments(P > 0.05); however, CON carcasses averaged largerribeye area (87 vs. 80 cm2, P < 0.01), greater Warner-Bratzler shear force measurement (WBSF; 3.46 vs. 3.19kg, P < 0.01), and smaller USDA marbling score (5.4vs. 6.2, P < 0.01), and less backfat thickness (1.64 vs.1.84 cm, P < 0.05) and yield grade (3.38 vs. 3.95, P< 0.01) than NE3 carcasses. Overall, CON cattle consumed393 kg less DM in the feedlot (1,250 vs. 1,643kg; P < 0.05). No treatment effects were observed fordaily methane (CH4; P = 0.62) or nitrous oxide (N2O; P= 0.7) emissions per steer. Assuming a constant emissionrate on a DMI basis throughout the course of thefeedlot trial, CON feedlot management resulted in a31% decrease in emissions per finished steer comparedwith NE3 management. Expressing CH4 emissions ona carbon dioxide equivalent (CO2-eq) basis revealed a1.10-kg CO2-eq difference per kilogram BW gain (5.02kg of NE3 vs. 3.92 kg of CON) between the 2 feedlotmanagement systems. Although the metabolic modifiersresulted in additional costs for the CON treatmentgroup, the cost per kilogram of feedlot BW gain wassignificantly less ($1.12/kg vs. $1.35/kg; P < 0.05) thanNE3. Both production systems satisfied some sustainabilitycriteria, although neither concurrently fulfilledall of the environmental, social, and economic goals ofagricultural sustainability. ©2011 American Society of Animal Science. All rights reserved.