RESUMEN
A spring calving herd consisting of about 350 beef cows, 14-16 breeding bulls, 60 replacement heifers and 112 steers were used to compare the whole-farm GHG emissions among calf-fed vs. yearling-fed production systems with and without growth implants. Carbon footprint ranged from 11.63 to 13.22 kg CO2e per kg live weight (19.87-22.52 kg CO2e per kg carcass weight). Enteric CH4 was the largest source of GHG emissions (53-54%), followed by manure N2O (20-22%), cropping N2O (11%), energy use CO2 (9-9.5%), and manure CH4 (4-6%). Beef cow accounted for 77% and 58% of the GHG emissions in the calf-fed and yearling-fed. Feeders accounted for the second highest GHG emissions (15% calf-fed; 35-36% yearling-fed). Implants reduced the carbon footprint by 4.9-5.1% compared with hormone-free. Calf-fed reduced the carbon footprint by 6.3-7.5% compared with yearling-fed. When expressed as kg CO2e per kg carcass weight per year the carbon footprint of calf-fed production was 73.9-76.1% lower than yearling-fed production, and calf-fed implanted was 85% lower than hormone-free yearling-fed. Reducing GHG emissions from beef production may be accomplished by improving the feed efficiency of the cow herd, decreasing the days on low quality feeds, and reducing the age at harvest of youthful cattle.