POLLUTION LOCATOR|Definitions of Animal Waste Categories

Scorecard's data on livestock operations is provided by the 1997 Census of Agriculture, which compiles county statistics for livestock based upon mail and telephone surveys conducted by the state agricultural statistics offices. Using this population data, Scorecard estimates waste levels based on information about the amount of waste different animals produce. Some states and counties lack information on certain animal types. Note that Scorecard cannot tell you the environmental health impacts of animal waste in your area, or assess the waste management methods of livestock operations. See Limits of Scorecard's Data on Livestock Operations for further information.

Animal Types

The Census of Agriculture compiles county statistics for different livestock types. The general animal type categories that Scorecard covers are cattle, hogs, sheep, and poultry. These categories often have a number of important sub-categories within them that are relevant to the calculation of animal waste data. For example, "cattle" refers to "all cattle and calves", which includes both beef and dairy animals. "Hogs" includes all swine and has no sub-categories related to age. "Poultry" consists of layer hens, broilers and other chicken, and turkeys. "Sheep" refers to "all sheep and lambs."

Number of Head

In agricultural terms, the number of head refers to the number of animals of a particular type. Each animal is counted as one "head". Number of head is equivalent to saying "population" for a certain animal type.

Steady-state Live Weight

Animals on a farm can be measured in two different ways. (1) The actual number of animals, or number of "head", with each head refering to one animal; or (2) by weight. The steady state live weight represents the collective weight of all animals at a facility and is actually more representative of the animals at the site. Animal operations are "permitted" for a certain number of animals, which cannot be exceeded. However, some hog facilities may contain only sows, others may be nurseries and contain only piglets. A certain number of adult hogs will produce a different amount of waste than piglets. To account for this, the steady state live weight can be divided by an average hog weight, producing an average number of animal "units" for an operation. Using this unit number, the amount of waste can be calculated by multiplying animal units by an average hog waste factor.

Amount of Waste (tons/yr)

Amount of waste is the weight, in tons, of feces and urine produced per year for a particular livestock type. Different types of animals produce different average amounts of waste per year. Scorecard uses waste factors to calculate the total amount of waste produced by a population of each particular animal type.

Volume of Waste (gallons/yr)

Volume of waste refers to the amount of space taken up by a given weight of animal waste produced, and is expressed in gallons per year. Different animal waste types have different densities and therefore, a given weight of waste from one animal type will occupy a different volume than the same weight of waste from a different animal type. Scorecard uses waste factors to calculate the volume of waste produced by a population of each particular animal type.

Amount of Nitrogen in Waste (pounds/yr)

This is the amount of nitrogen, in pounds, that can be found in a given amount (weight) of animal waste and can be calculated using a different nitrogen factor for each waste type. It is important to note that this quantity will differ from the amount of nitrogen sprayed onto fields because a significant quantity of nitrogen is volatilized before it is applied.

Inorganic nitrogen predominately occurs as either ammonia (NH3) or nitrate (NO3), and is usually the limiting nutrient in marine ecosystems. A limiting nutrient is one which "limits" or controls the growth of primary producers, i.e., algae and other plants. Under conditions of N limitation, increases in nitrogen from any source, can result in rapid and excessive increases in algal growth. When these algae die, the bacteria responsible for decomposition consume dissolved oxygen in the water column. Therefore, a massive "bloom" of algae can cause a severe drop in the level of dissolved oxygen, the result being that not enough oxygen is left for fish, crabs and other animals to breathe.

Nitrogen Lost to Atmosphere (pounds/yr)

The nitrogen in animal waste goes through many conversions-- and much of it can be volatilized, or lost to the air, as ammonia (NH3). Ammonia volatilization occurs while the waste is still in the hoghouse, and the fans used for ventilation pump the nitrogen-laden air to the external atmosphere. Further volatilization occurs from the lagoon surface once the waste is transported to the lagoon. Finally, the process of spraying the lagoon slurry onto a field also causes loss of ammonia to the atmosphere. These rates of loss to the atmosphere have been estimated for different animals. To obtain the total nitrogen lost, the number of animals is multiplied by the rate constant.

Amount of Phosphorus in Waste (pounds/yr)

This is the amount of phosphorus, in pounds, that can be found in a given amount (weight) of animal waste and can be calculated using a different phosphorus factor for each waste type.

Animal waste contains a significant amount of phosphorus, a nutrient which often limits algal growth in freshwater systems. Under phosphorus limited conditions, increases in phosphorus can spur the growth of algae. When these algae die, the bacteria responsible for decomposition consume dissolved oxygen in the water column. Therefore, a massive "bloom" of algae can cause a severe drop in the level of dissolved oxygen, the result being that not enough oxygen is left for fish, crabs and other animals to breathe.