From: The inefficiency of animal foods - food conversion rates (PDF file)

Commentators differ in their assessment of the efficiency of animal farming because they apply different criteria to their calculations. Those sympathetic to the livestock industry might omit some factors - perhaps losses through disease or transport costs for feed - that a more critical observer might include. It also depends upon the type of diet on which animals are fed and the proportion of their lives in which they consume high protein feeds. For example, a vested interest organisation such as the US National Cattlemen’s Beef Association has claimed that it takes only 4.5 kg of grain to produce 1 kg of beef raised intensively in a US feedlot. On the other hand, the US Department of Agricultural Economic Research Service puts the figure at 16 kg of grain to produce 1 kg of beef.

Similarly, the UK poultry industry claims that through selective breeding it has improved feed efficiency to the point where it takes only 1.6 kg of feed to produce 1 kg of weight gain per animal, but this takes no account of the fact that by its own calculation the total edible meat yield from each bird is only 33.7 per cent of the total carcase. Once the inedible part of the dead animal is taken into account, the ratio of grain to meat becomes considerably higher. Given that there is no such thing as the ultimate accurate scientific calculation, the following assessment by the US Council for Agricultural Science and Technology (CAST) - an organisation that would claim to have no bias - gives a useful indication. The statistics, based upon a survey of several other studies, are particularly relevant since they include conversion rates for feed to finished product, as well as the more often quoted feed to weight of animal when slaughtered.

Once again, assessments vary as to exactly how much more land it takes to produce meat than it does to provide the equivalent amount of calories by growing food directly for human consumption. According to the World Health Organisation (WHO) and the Food and Agriculture Organisation of the United Nations (FAO), ‘the number of people fed in a year per hectare ranges from 22 for potatoes and 19 for rice down to 1 and 2 people respectively for beef and lamb’. 72 While it would be wrong to conclude that a restricted diet of rice or potatoes alone will provide all the necessary micronutrients for human health, this can be taken, nevertheless, as another clear indication of how the answer to feeding hungry people is not to move towards a largely meat-based diet. A more sensible policy would be to base dietary goals on the traditional eating patterns of those populations in developing countries who, despite relative poverty, do have enough food to maintain good health. It would be unusual for livestock products to play more than a minor part in such diets, which consist for the most part of grains, legumes, fruits, vegetables and other plant products. Improving their quality and variety offers a more rational approach to world food production than attempting to emulate the unsustainable model practised in the developed world.