AN ACRE A MEAL? - MEAT: A Benign Extravagance - page 34

or not required for it. Even the archetypal American feedlot cow is not fed entirely on grain
because cows need fibre. 'In the total feedlot system' says David Pimentel, 'the protein fed
to the beef and breeding stock consists of about 42 per cent forage with the remainder be-
ing grain'; 47 CAST provides a similar figure. Moreover, feedlot cows normally spend the
first half, or even two thirds of their life on grass, where they have already gained 50 to 70
per cent of their weight. 48 If we round this off to 60 per cent it means that human edible
food constitutes only 24 per cent of the animal's entire intake - which in practice brings a
8:1 feed conversion ratio abruptly down to about 2:1. However, much of the forage fed to
US feedlot cows is lucerne derived from unsustainably irrigated arable fields: if we count
this component of a feedlot cow's diet as equivalent to human food, then the effective ratio
of human edible feed to meat and other animal products in US feedlot beef comes to about
3.2:1.
CAST v CIWF: The Result
The information provided in the foregoing pages is, hopefully, sufficient to convince
the reader that whatever the metabolic feed conversion ratio may be for any breed of an-
imal, in the real world there is a multiplicity of factors that can and regularly does lower
the ratio significantly, sometimes to a point where the inefficiency of livestock rearing is
negligible, or even negative.
But what of our rule of thumb figure, so casually passed off as ten to one by some com-
mentators? Does this require revision, or should it be abandoned? Is it possible to arrive at
a global aggregate efficiency ratio for livestock as a whole?
In 1979, David Pimentel estimated that more than 60 per cent of the world's livestock
protein 'comes from animals fed grasses and forages that cannot be utilized by man. The re-
mainder comes from livestock fed plant and animal protein that is suitable food for man.' 49
This puts the matter into context, but it does not really help us, not only because it is out
of date, but also because we still do not know at what efficiency the 40 per cent was being
converted into human food. In 1997, a major FAO census on livestock concluded:
If it is assumed that all 966 million tonnes of cereals, roots and tubers used for
livestock are edible for humans (in effect they are not, as there are considerable pre-
paration losses in milling etc), then livestock gets 74 million tons of edible protein.
On the positive side, the 199 million of meat, 532 million tons of milk and 53 million
tons of eggs produced globally in 1996 contain 53 million tons of protein. 50
Assuming that this figure is correct, it means that the global aggregate conversion ratio
of human-edible feed to human edible meat is 74:53, or 1.4:1 (the figure has since been