Animals are Inefficient Converters of Food
It is widely accepted that farmed animals consume more food than they produce.
The question is not “IF” animals are inefficient food converters, but “HOW” inefficient are they? And are those inefficiencies worth having meat?
While these issues are generally discussed in terms of “efficiency” not “inefficiency,” based on the inherent loss of crops and natural resources involved in producing animal sourced foods (ASF), “inefficiency” is a far more accurate term.
Inefficiency is determined in large part by Feed Conversion Ratios (FCRs), which measure the amount of feed crops needed to produce a unit of meat/ASF.
Research on FCRs yield a wide variation in numbers. As interdisciplinary scientist Valcav Smil explains, “all unqualified single figures are misleading. Diversity of breeds, environments, and feeding practices are the necessity of making simplifying assumptions… means that a definite rate is valid only for a particular animal, herd, or flock.” (p.146)
This page will explain some of the factors that produce such wide variation and make recommendations based on the most useful measures.
The numbers below represent FCRs for crop-fed farmed animals. In other words, how much more food animals consume than they produce. Typical feed crops are grains and legumes: corn, soy, and wheat.
These numbers are important as crop-fed, factory/conventionally-farmed animals are the norm, representing the overwhelming majority (>98%) of meat produced in the United States. Furthermore, the global growth-rate of meat is alarmingly high. (There are different, but still serious concerns about grass-fed cattle).
Mainstream Feed Conversion Ratios
- Chickens – 2x-5x
- Pigs – 4x-9x
- Cows – 6x-25x
*These are mainstream/middle-range estimates.
Live weight FCRs – will have lower ratios because they represent the number of pounds in crop that animals consume to gain one pound while they are alive.
Edible weight FCRs – will have higher ratios because they more accurately represent the amount ready-to-eat of meat produced after slaughter and processing.
Even with edible weight, there will be variations such as carcass/hanging weight and final/take-home (which is roughly half of live weight for pigs and one-third for cows — thus doubling and tripling the inefficiency ratios — more when boneless). (detailed chart)
Most of the caloric energy animals consume is used to fuel their metabolism and to form bones, cartilage, feathers, fluids, and other non-edible parts. Thus, the inefficiencies more than double when liquid weight is removed – the weight of the water, blood, and other bodily fluids. Further weight loss occurs with the removal of bones and other non-consumable body parts.
Often times, the food industry will publish the low end FCRs, which minimizes the perceived waste. Those without a vested interest in animal agriculture and/or industry critics are more likely to publish the higher (more accurate) post-processing carcass or boneless numbers.
Even if method is held constant, there will be a variation in FCRs. Other factors that affect FCRs include: type/quality/moisture of feed, animal age, breed, activity level, number of offspring, and a host of other variables.
There is a great deal of focus on improving these factors in reduce inefficiencies, but the inherent waste of cycling crops through animals remains. Adjusting these factors merely shaves down some of the numbers without addressing the core issue that feeding animals to produce food is a massive net loss of available global calories and protein.
Consider how telling it is that a 2:1 loss of food crops is considered very efficient and cause to celebrate. When we talk food waste, would we consider losing half of all crops “good?”
FCR Mainstream Examples
- 6:1 – beef cows – Beef Magazine (industry)
- 6:1 – beef cows, 3.4:1 – pigs, 2:1 – poultry – Noble Foundation (industry)
- 7:1 – beef cows, 4:1 – pigs, 2-1 – chickens – Brown (advocate)
- 8-12:1 – beef cows, 5-6.5:1 – pigs, 2-2.5:1 – chickens – Smil (p.157) via Cassidy (p.6)
Edible Weight (more accurate)
- 16:1 – beef cows – Lappe (Diet for a Small Plant, 1991, p.69) – (frequently-cited advocate)
- 25:1 – beef cows, 9.4:1 – pigs, 4.5:1 – chickens – Smil (EM/2008 via UKY) (researcher)
More Comprehensive FCRs
Percent/Units of Edible Output per 100 Units of Feed
- Poultry – Calories – 11% – Protein 20%
- Pigs – Calories – 10% – Protein 15%
- Cows/Beef – Calories – 1% – Protein – 4%
Source: World Resources Institute (w/UN & WB): Creating a Sustainable Food Future, p.37
New, more comprehensive methods show that even the high-end of commonly cited FCRs are highly conservative.
Perhaps the most accurate way to gauge the inefficiencies of animal sourced food production is to calculate the sector-wide phytomass (plant biomass) energy that goes into animal production versus how much energy comes out in the form of animal sourced foods.
In other words, what portion of plant energy dedicated to raising animals becomes edible calories in the form of meat, dairy, and eggs. This method looks beyond costs associated with a single animal and instead at the the energy flows in the broader food system.
By calculating the fates and flows of phytomass energy on a macro scale, it is possible to track how and where food energy is being wasted in the production of various food products.
Energy Flows in the Broader Food System
The inefficiencies expressed as “units of edible output per 100 units of feed input,” are lower than the previous feed conversion calculations not only because the inefficiencies are based on energy flows from plant phytomass to edible animal parts, but because they factor in feed that gets wasted before it reaches livestock animals, the plant mass that goes to non-feed purposes such as bedding, the energy grass and other forage that goes into feeding livestock, and the energy needed to support animal production beyond just producing animals. Many animals involved in livestock production do not directly produce food, such as animals that are inevitably culled, that die before reaching maturity, and that are used in breeding. (Stefan Wirsenius, Human Use of Land and Organic Materials, 2000)
Wirsenius’s work takes a macro look at the food system, calculating how much phytomass is appropriated for food production in the form of pasture and cropland, related to how much food is produced. This method is helpful because it gets at the total food energy that into animal agriculture as a system.
According to previous estimates, over two-thirds of phytomass energy appropriation is dedicated to farmed animal production, despite that the sector only produces about 13% of total food calories.
In the same way that one can get an accurate estimate of how much a college education will cost by including the cost of housing, supplies, and other living expenses with the cost of tuition, so too can one get a more accurate estimate of the inefficiency with which farmed animals convert plants to animal sourced foods by considering the feed needs (including pasture and grain) of the animal agriculture sub-sectors.
Another strength in Wirsenius’s method is that, unlike the previous feed conversion methods that only calculate conversions in terms of feed such as soy or corn, it also factors grass and forage into its calculations.
Grain weight is easier to quantify since producers tend to purchase and feed it to animals in given weights, whereas the amount of grass and forage animals consume on pasture can only be roughly estimated.
In this gross energy calculation that looks at all phytomass appropriation involved in food production, pasture land is the largest source of phytomass energy. This, combined with the inherent feed conversion inefficiencies of cattle, are one of the reasons why beef production is one of the least efficient forms of food production.
While phytomass that is not in not edible to humans is often discounted in determining the crop costs and opportunity costs of using animals for food, much of the land cleared for pasture could also be used for crop production, so it should be thought of as forgone plant-based food production. There are also significant environmental impacts related to clearing wilderness areas for pasture land/
But even if we were to adjust these calculations to remove the phytomass energy derived from non-edible material, such as grass on open pasture or the straw that is used as bedding in some animal operations, there would still be a dramatic difference in the quantity of food that can be yielded as edible calories for human consumption from livestock food and from plant-based protein alternatives.
Conclusion: Feeding People
Regardless of the exact numbers, producing crops (soy, corn, wheat, etc.) for animal feed is many times more resource-intensive than using crops for direct human consumption. While there are perilous trade-offs related to fuel vs. food, a more serious concern for a variety of reasons is feed vs. food.
With 75% of all agricultural land used for animal production—and more than a third of global calories and half of global protein inefficiently used as animal feed —the impact of increasing global meat consumption is monumental. (ERL p.2-3)
For more on the opportunity costs of animal agriculture, please see: Cassidy’s “Redefining Agricultural Yields: From Tonnes to People Nourished Per Hectare.”
“[F]eed 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.”
“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.”
Cassidy, Emily et al, “Redefining Agricultural Yields: From Tonnes to People Nourished Per Hectare.” Environmental Research Letters, V. 8(3). IOPScience, September 2013, p. 2-3. http://iopscience.iop.org/1748-9326/8/3/034015
Smil, Vaclav, Feeding the World: A Challenge for the 21st Century, MIT Press, 2000, p. 145-157.
Yacoubou, Jeanne, “Factors Involved in Calculating Grain:Meat Conversion Ratios.” Vegetarian Resource Group, last accessed October 2015. www.vrg.org/environment/grain_meat_conversion_ratios.php
Last updated October 26, 2015