Cattle entering the feedlot for finishing eat a diet that contains corn along with by-products (such as distillers grains leftover after ethanol production), vitamins and minerals, and forage or roughage (such as hay). Grainfinished cattle remain in the feedlot for approximately four to six months and are sent for harvesting at 14 to 22 months of age. Grain-finished cattle reach market weight faster than grass-finished1,2
because the diet the animals receive is higher in energy, which results in more efficient weight gain. In contrast, grass-finished cattle gain at a slower rate due to the forage-based diet they eat and typically go to harvest at 20-26 months of age and at a lower weight than grain-finished animals. Grassfinished cattle may finish either faster or slower than this age range depending on the forage and grass resources available to the beef producer (e.g., the growing season is shorter in northern U.S. states, which may shorten the finishing period and lead to lighter weights at harvest). The difference in harvest weights translates into different numbers of U.S. citizens that could be fed per animal (Table 1
). Utilizing forage as the primary source of feed also contributes to an increased carbon footprint for grass-finished beef,2 because high forage diets (e.g., grass) produce more methane emissions from the animal’s digestive tract than higher-energy, grain-based diets. The combination of consuming a higher energy, lower forage diet, shorter time spent on feed during finishing, and heavier carcass weights translate into a 18.5 to 67.5% lower carbon footprint for grain-finished beef as compared to grass-finished beef.1,2
Even though grass-finished beef has a higher carbon footprint, it does have some sustainability advantages. Grass-finished animals utilize plants that are inedible by humans as the primary source of energy and nutrients for their entire lifetimes. In contrast, 82% of feed intake per unit of carcass weight for conventional animals occurs from grazing forage, pasture or rangeland.5 Beef cattle can utilize forage grown on land not suitable for crop production, and thus produce human edible food from a resource that could not otherwise be used to produce food. Additionally, grasslands and pastures can sequester carbon dioxide from the atmosphere, which can help to mitigate global climate change. Research has shown an advantage for grass-finished beef production over grain-finished beef production when expressing feed conversion as human edible energy returned per unit of human edible energy consumed by the cattle.2,6
Accounting for carbon sequestration of grass-finished beef that is finished on pastures could lower the carbon footprint of grass-finished beef by 42%.2 Ultimately, tradeoffs exist between the two beef production systems; however, beef producers using either system can sustainably meet consumer demand for beef by utilizing the resources they have in their part of the country.