Fossil energy is expended in livestock production systems. For example, broiler chicken production is the most efficient, with an input of 4 kcal of fossil energy for each 1 kcal of broiler protein produced. The broiler system is primarily dependent on grain. Turkey, also a grain-fed system, is next in efficiency, with a ratio of 10:1. Milk production, based on a mixture of two-thirds grain and one-third forage, is relatively efficient, with a ratio of 14:1. Both pork and egg production also depend on grain. Pork production has a ratio of 14:1, whereas egg production has a 39:1 ratio.

livestock systems depending most heavily on forage but also using significant amounts of grain are the beef and lamb production systems. The beef system has a ratio of 40:1, while the lamb has the highest, with a ratio of 57:1. If these animals were fed on only good-quality pasture, the energy inputs could be reduced by about half.

Average fossil energy input for all the animal protein production systems studied is 25 kcal fossil energy input per 1 kcal of protein produced. This energy input is more than 11 times greater than that for grain protein production, which is about 2.2 kcal of fossil energy input per 1 kcal of plant protein produced.

http://ajcn.nutrition.org/content/78/3/660S.full#T2