Saturday, October 20, 2007

Calling All Green Carnivores

Are you trying to be greener? Are you an immutable carnivore? Me too.

Struggling intermittently with my conscience, I am trying to take account of two factors that should have some bearing on my dietary decision-making. I assume there’s some connection between the two factors, but I don’t know what it is.

First, there’s the efficiency of the meat production. How much food must the animal consume per pound of meat that it produces for people? In a situation of food scarcity and high human population density, it makes no sense for a person to eat meat from animals that themselves consume a great deal of food fit for human consumption. We should eat the corn, for example, instead of feeding it to the pigs. However, I’m not about to become a , so the best sacrifice I’m willing to make is to limit my meat to efficient types. The conventional definition of fed utilization is “the body weight gain per units of energy intake.”

So far, I haven’t found a source on the Internet giving the comparative efficiencies of the whole list of animals. I assume that fish are okay, unless one takes account of the fuel necessary to maintain fishing fleets, freezers, and the like — which I’m not taking into account here. (A thorough green researcher would come up with a single equation that would combine all these factors and give a single efficiency number for each animal that human beings consume, but that hasn’t been done yet, apparently.)

One article looks just at poultry, comparing the efficiencies of chickens, turkeys and ducks at 7 weeks of age. The turkey broiler is most efficient in feed use, but there are other costs that make it less attractive to farmers. The chicken broiler edible meat is cheaper to produce than meat from turkeys and ducks. However, turkeys have less body fat, so some people would prefer their meat for reasons of health.

We turn now to mammals. It seems that animals fed from their mother’s milk costs at least fifty percent more energy than that made from forage. This is why are highly efficient; they eat forage quite early, even before they are weaned. Jackrabbits are 1.82 times more efficient than the range sheep and about 2.04 times more efficient than the range .

C. Wayne Cook writes: “It has been determined that beef, lamb, and domestic rabbit have an average of 1316, 1040, and 792 kcal per pound of body meat, respectively.” His paper tries to figure out how efficient rabbit-meat production would be, given specified conditions of feeding, rates of reproduction, length of lactation, etc. This is too complicated for me to work out. However, it is comforting to realize that rabbits as livestock are about 2.2 times more efficient than sheep and about 2.8 times more efficient than cattle. (Comforting, I say, because I have already figured out that I’ve got to stop eating beef.) However, I have not bought and cooked a rabbit for many years and wouldn’t know where to obtain one. Maybe I’ll start looking.

Second, there’s the matter of , a far more serious form of than even carbon dioxide. produce methane by digesting a forage-based diet through rumen fermentation. They belch and fart, with the belching accounting for most of the methane emissions. In the world, between 15-20 percent of the methane in the atmosphere comes from animals – mostly ruminants.

A good deal depends on the quality of the forage, and according to R.A. Leng,

“The majority of the world’s ruminants depend over their lifetime on forages that can be described only as poor quality, in which the limitations to production are a low protein supply from the microbial ecosystem and a virtual absence of dietary bypass protein.”

Fortunately, it is possible to improve the microbial growth efficiency and therefore the protein content of animal feed. Doing so on a big scale would markedly influence the amount of methane in the atmosphere.

However, I am not going to wait. I must adjust my right away, taking account of the comparative amounts of methane produced by various domestic . I am pleased to list here the estimates of methane emissions from animals, taking account of the different types of forage available in developed and developing countries. Here are figures from a table Leng has produced, showing the methane produced in kg per head. These numbers in absolute terms may mean little, but their relative size tells me a lot:

Cattle: developed countries 55
Cattle: developing countries 35
Buffaloes 50
Sheep: developed countries 8
Sheep: developing countries, Australia 5
Goats 5
Camels 58
Pigs: developed countries 1-5
Pigs: developing countries 1-0
Horses 18
Mules, asses 10
Humans 0- .05
Wild ruminants and large herbivores 1-50

Well, that tells me a lot. I will eat fish, poultry, sheep, goats, rabbits, and pigs. I will not longer eat beef, bison, camels, horses, or most wild ruminants (deer, moose, boar, or elk). Bear that in mind when you invite me over.

Unfortunately, milk cows apparently produce methane as much as cattle. What do I do about dairy products? Soy milk, I guess. And goat and sheep cheese. I already eat a lot of chevre, so I'm halfway there. But I'll miss the Limburger.



Blogger Fat Knowledge said...

I was just reading Vaclav Smil's Feeding the World and he looks into the efficiency of using various animals as food sources in Chapter 5 of his book. You might find an answer to your question there.

You had left a question on this post, and I just wanted to let you know that the numbers do include the impact of methane as well as CO2. I should have probably labeled the values as "CO2 equivalent tonnes" rather than "CO2 tonnes" to make that more obvious.

2:31 PM  

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