Factors Involved in Calculating Grain:Meat Conversion Ratios
By Jeanne Yacoubou, MS
VRG Research Director
An environmental argument for vegetarianism often involves a discussion of the relative efficiency by which livestock convert grains and legumes that they consume into meat eaten by some people. The process of converting grain, legumes, and their byproducts into human-edible meat is commonly expressed as a grain:meat conversion ratio.
While researching the quantities and types of feedstuffs needed by livestock to produce meat, the writer noticed wide discrepancies in grain:meat ratios calculated by various scientists, government agencies, nonprofits, and agribusiness. Some ratios ran as high as 16 pounds of grain per pound of meat to a low of 0.3 pounds of grain per pound of meat. Thus began an investigation into some of the many factors involved in calculating grain:meat conversion ratios. The investigation revealed the importance of considering the assumptions implicit in all of the determinations. Without a working knowledge of authors' assumptions, the ratios lack meaning. When two competing values based on different assumptions are viewed together, they cannot be accurately compared.
One of the major reasons for differences in grain:meat conversion ratios stems from the definition of the word feed. The United States Department of Agriculture (USDA) publishes annual statistics at www.nass.usda.gov/Publications/Ag_Statistics that discuss feed fed to livestock. It is not made explicitly clear how feed is defined for the purposes of these tables. Personal email communication between the writer and several USDA employees confirmed that feed is NOT synonymous with "concentrates" such as grains and legumes. Some USDA tables may use "as-fed" feed values which means the moisture content of the feed (which may vary between 7 and 70% of the feed weight itself) is included. Similar tables found in other sources may be based on "dry matter weight" which excludes all weight of the feedstuff due to water. Feed may have been assumed to be synonymous with grain, and/or to contain moisture, by some whose ratios are very large.
A large portion of the diets of ruminant livestock, including cattle, sheep and goats, consists of feedstuffs that are not edible by humans such as pasture, hay and crop residues (i.e., corn stalks). In some regions of the world, ruminants subsist entirely on these. However, most ruminant livestock produced under intensive conditions, (i.e., feedlots), do spend a significant part of their life eating grains and soybean byproducts, such as soybean meal and soybean oil, that are human-edible.
The situation is different with monogastric livestock, (i.e., animals with one stomach), such as hogs and poultry. Under intensive rearing conditions that are common in the United States, their diet consists almost exclusively of human-edible grains and legumes. So for these species, their feed is almost all grain and legume. Consequently, tables such as those published by the USDA containing values of total feed consumed and total number of (monogastric) livestock produced, do provide a rough estimate for grain:meat ratios (ignoring moisture content). Such tables cannot provide accurate ratios for ruminant livestock such as cattle and dairy cows.
When considering ratios, it is also important to determine if they are extrapolations based on a single stage of an animal's life cycle spent on a feedlot, to the entire lifetime of the animal. Although many cattle spend the last few months of their lives on feedlots, most of their lifetime had been spent grazing on pasture. Large ratios do not reflect this fact.
Thirdly, it is important to know which weight (referred to as live, carcass or boneless cut in agribusiness) was used in the ratio's calculation. Animal producers typically analyze "the amount of feed consumed per pound of live weight gain" when making economic comparisons between the efficiencies of different diets, or comparisons between weight gains in animal groups on different dietary regimes. Carcass weight is closer to the actual amount of meat produced by an animal that is consumable by humans while boneless meat cuts (considering fat trimmings here as insignificant) are the most accurate. When based on live weights, smaller feed:meat ratios are often calculated, while larger ones could imply that carcass weight or boneless cut weight was used, assuming all other variables were constant in the cases under consideration.
For those interested in reading about the animal industry's feed:meat ratios using yet another indicator (i.e., price of corn and price of live weight unit produced) as well as other issues related to this topic, see the 2009 Reference Issue and Buyer's Guide of Feedstuffs magazine available at www.feedstuffs.com.