A pound of flesh — a puzzle about estimates, energy, and life

3 thoughts on “A pound of flesh — a puzzle about estimates, energy, and life”

  1. Here’s the answer to the puzzle: It’s the *natural* lifespan of animals that scales as M^(1/4), not the actual lifespan of farm animals, which is far shorter. The lifespan of beef cattle is about 2 years; the natural lifespan is about 20 years. “Fattening” Pigs: about 6-7 months versus 20 years. “Broiler” chickens: 40 days versus 8-15 years. A chicken is about 300x less massive than a cow, but its lifespan on a farm isn’t 300^(1/4) = 4.2x shorter, but rather about 20x shorter. (Lifespan numbers: http://www.four-paws.us/campaigns/farm-animals-/farm-animal-life-expectancy/)

  2. I wonder, shouldn’t the industrial parameter b also be dependent on mass? If cows are 300x more massive than a cow, then for b to be constant, you would need to house 300 chickens in the same space as a single cow. While I know the current industry standards are pretty horrendous as far as spacing for chickens go, I don’t think they store 300 chickens in the same space as a cow, although I’m not sure: https://www.farmsanctuary.org/learn/factory-farming/chickens/

    1. Hi Fehmi,
      I don’t know much about cows or chickens, but I would guess that you *could* keep a lot of chickens in the space needed by one cow! From this: https://extension.unh.edu/resources/files/Resource000471_Rep493.pdf, a broiler chicken needs 3-4 sq. feet, and a beef cow needs about 200 sq. ft (housing + exercise), a ratio of 50-70, which isn’t too far from 300. Furthermore, in case the relevant thing is the volume of required space, the ratio becomes even higher (50^1.5 = 350!). Moreover, I doubt that the “industrial” power needed to keep a unit mass of animal alive is dominated by the space the animal needs, but rather by the energy requirements of growing the animal’s food, which are probably pretty similar for most common animal types. (It would be good to read a simple but thorough analysis of this.) I wouldn’t be surprised, though, if there are subtle mass dependences (or economies of scale) that come into this, but I can’t guess which way they would go!
      Raghu

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