Factors Involved in Calculating Grain: Meat Conversion Ratios
An environmental argument for vegetarianism often involves discussing how livestock consume grains and legumes so they may grow and become meat for people to eat, when it would be more efficient for people to consume those grains and legumes directly. The process of converting grain, legumes, and their byproducts into human-edible meat is commonly expressed as a grain:meat conversion ratio.
In researching the quantities and types of feedstuffs that livestock need to produce meat, there are wide discrepancies in the grain:meat ratios that various scientists, government agencies, nonprofits, and agribusiness have calculated. Some ratios ran as high as 16 pounds of grain to produce a pound of meat, while others were as low as 0.3 pounds of grain to produce a pound of meat.
So, what are some of the many factors that affect calculating grain:meat conversion ratios? Without knowing what the author used to calculate the ratios, the ratios cannot be accurately compared.
One of the major reasons there are differences in grain:meat conversion ratios is because there are varying definitions 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 provided to livestock. It is not made explicitly clear how 'feed' is defined for the purposes of these tables. Personal e-mail communications 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 is included. (The moisture content of the feed may vary between 7 and 70 percent of the feed weight itself.) Similar tables from other sources may be based on 'dry matter weight,' which excludes all weight due to water. Feed may have been assumed to be synonymous with grain and/or to contain moisture, and this could explain why some of the grain: meat conversion ratios are very large.
Ruminant livestock-including cattle, sheep, and goats-often consume diets that consist largely of feedstuffs that humans can't consume, such as pasture, hay, and crop residues (i.e., cornstalks). In some regions of the world, ruminants subsist entirely on these feedstuffs. However, most ruminant livestock produced under intensive conditions (i.e., feedlots) spend much of their lives eating grains and soybean byproducts, such as soybean meal and soybean oil, that humans could consume.
The situation is different with monogastric livestock (i.e., animals with one stomach), such as hogs and poultry. Under the intensive rearing conditions that are common in the United States, these species' diets consist almost exclusively of human-edible grains and legumes. Consequently, tables, such as those that the USDA publishes, that address 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.
Furthermore, it is vital 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 they make economic comparisons between the efficiencies of different diets or when they compare weight gains in animal groups on different dietary regimes. Carcass weight is closer to the actual amount of meat that a consumable animal produces, while boneless meat cuts (considering fat trimmings here as insignificant) are the most accurate. When calculations are based on live weights, the result is often smaller feed:meat ratios. In contrast, larger ratios could imply that carcass weight or boneless cut weight was used to calculate the amounts. This is assuming that all other variables involved in the cases under consideration are constant.
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.