Energy Use in Livestock Production

The amount of energy expended in livestock production systems depends mainly on the type of animal itself, on its reproductive system and on the type of feed. Animals vary in the efficiency with which they convert plant energy and protein into animal protein and fat. In addition, they vary in their ability to utilize different plant foods.

On a worldwide basis, about 34 %, i.e. 44 million tonnes, of the protein consumed by humans is animal protein, from which 60 % come from animals fed grasses and forages that cannot be utilized by humans (Pimentel and Pimentel,1996). The remainder comes from plant and animal protein fed to livestock but which is suitable food for humans. Livestock consume 50 million tonnes of plant and animal protein suitable for humans, yielding an estimated 41 million tonnes of livestock protein. This means that 1,2 kg of dry plant protein suitable for human consumption is converted into 1 kg of animal protein (Pimentel and Pimentel, 1996).

Obviously, this conversion from plant to animal protein is not as efficient when compared with direct consumption of plant proteins by humans. There are, however, other benefits to be considered in raising livestock besides simply the energy their production consumes: meat can provide concentrated sources of protein and other nutrients (i.e. iron) essential for human nutrition that are more difficult and/or less efficient to obtain from plant sources. Livestock also produce manure, which is a farm-based and organic source of nutrients that can be used to replenish the soil used to produce crops; thereby reducing the requirement for high-energy synthetic fertilizers. Livestock can also be used to consume feed (i.e. barley) which is in surplus in one region, thereby releasing supplies of other higher protein feeds (i.e. soybeans) to other regions experiencing a deficit in protein requirements. In a world where undernourishment is a reality for millions of people, it is essential that meat production be as efficient as possible in all respects in order to maximize the availability of protein and calorie food sources consumable by humans.

Range Beef production

When looking at the ratio of fossil fuel energy expended per kcal of protein produced, range beef production is the most efficient of all animal protein production systems (see Table 1). Range production of meat is that which takes place largely on open-range or pasture which is extensively managed, that is to say with the minimum of inputs and/or intervention by the farmer.

Table 1 - Fossil fuel energy input per animal protein production output for various livestock systems

Animal production system	Kcal energy input / kcal protein output
Range beef	10 : 1
Chicken	16 : 1
Range lamb	16 : 1
Milk	19 : 1
Eggs	28 : 1
Beef	35 : 1
Pork	68 : 1
Lamb	188 : 1

Source: Pimentel and Pimentel, 1996

One major advantage of husbanding beef animals that could explain this efficiency is that they convert forage grasses and shrubs that are unsuitable for human consumption into animal protein. An excellent pastureland in Texas can produce 2,2 kg/ha of beef protein per year while average grasslands range from as little as 0,2 to 0,5 kg/ha per year. Another major advantage explaining the efficiency of this system is that range beef animals have to move and harvest their own feed, while under feedlot conditions the feed is brought to the animals. Hence, range beef require only 10 kJ of fossil fuel per kJ of range beef protein produced, as opposed to 35 kJ per kJ of feedlot beef protein. (Pimentel and Pimentel, 1996). In this case, the fossil fuel energy for range beef is mainly used for pickup trucks used in herding the beef cattle on the range.

Range lamb production

Like beef, sheep can be maintained on rangeland, resulting also in a very efficient animal protein production system. But sheep require a large land area for grazing: in Utah, for example, it takes nearly 6 ha and a feed energy input of 3,075 MJ to produce 1 kg of lamb protein. Lambs and sheep, however, also produce wool during their growing period, which is converted into clothing and other materials made from natural fibres.

As with range beef, the fossil fuel energy input to produce range lamb protein is very small, amounting to only 16 kJ per kJ of lamb protein produced and is used primarily for fuel for pickup trucks in herding the sheep.

Chicken production

Chicken (broiler) production is also one of the most efficient of all the animal protein production systems. This efficiency results from the fact that the hen produces a large number of offspring (230-plus eggs per year), that less than 10 weeks are necessary to feed a broiler up to marketable weight and that broilers make efficient use of their feed (broilers convert about 2 kg of feed (dry) into 1 kg of live weight). Chicken production is also very efficient in its use of labor.

Milk production

Additional considerations in the production of milk are the energy expenditures for tractors, trucks, manure movers, and electricity other equipment such motors and pumps. In the US, the fossil fuel energy input for feed and animal production requires about 19 kJ per kJ of milk protein produced.

Egg production

Next to chickens and milk, eggs are the most efficiently produced type of animal protein. An estimated 27 percent of plant protein fed to the chickens is converted into egg protein, 2,6 kg of grain being required per kg of egg produced (Pimentel and Pimentel, 1996). An important consideration, however, is that 70 % of the plant protein fed to chickens is suitable for human consumption.

Beef production

Pork production

Pork production is one of the less efficient animal protein production systems in terms of energy consumed. Hogs convert only about 14 % of the plant protein fed to them into pork protein, i.e. 6,9 kg of feed protein are needed to produce 1 kg of pork protein. Also, their fossil fuel energy input is calculated to be about 68 kJ feed per kJ of pork produced, a high ratio for animal protein production.

But hog production also presents some advantages. One of them is that, although much of the protein fed to hogs is suitable for human consumption, they can be fed satisfactorily on food wastes, such as table scraps or garbage, or surplus foods produced from gardens during the growing seasons. Another advantage is that hogs produce litters ranging from 8 to 12 piglets. This litter size substantially reduces the number of animals in the breeding herd that must be fed and maintained to supply the young that will be reared solely for meat. Maintaining a breeding herd has high costs in both feed and maintenance energy.

Lamb production

Feedlot lamb protein production is certainly the least efficient of the livestock protein production systems. The only slight advantage that sheep production would have over beef production, for example, is that sheep usually produce twins. In fact, one breed of sheep can even produce 4 offspring per lambing. If this characteristic could be bred into all commercial breeds of sheep, the efficiency of lamb protein production would be increased because of the size of the breeding flock and the energy expenditure to maintain it could be reduced.