Livestock grazing comparison
Livestock grazing comparison is a method of comparing the numbers and density of livestock grazing in agriculture. Various units of measurement are used, usually based on the grazing equivalent of one adult cow, or in some areas on that of one sheep. Many different schemes exist, giving various values to the grazing effect of different types of animal.
Livestock grazing comparison units are used for assessing the overall effect on grazing land of different types of animals (or of mixtures of animals), expressed either as a total for a whole field or farm, or as units per hectare (ha) or acre. For example, using UK government Livestock Units (LUs) from the 2003 scheme a particular 10 ha (25-acre) pasture field might be able to support 15 adult cattle or 25 horses or 100 sheep: in that scheme each of these would be regarded as being 15 LUs, or 1.5 LUs per hectare (about 0.6 LUs per acre).
Different species (and breeds) of livestock do not all graze in the same way, and this is also taken into account when deciding the appropriate number of units for grazing land. For example, horses naturally graze unevenly, eating short grass areas first and only grazing longer turf if there is insufficient short grass; cattle graze longer grass preferentially, tending to produce a uniform sward; goats tend to browse shrubs if these are available. As these feeding styles are complementary, a pasture may therefore support slightly more units of mixed species than of each species separately. Another consequence of different grazing styles is variation between species in the number of units that can lead to overgrazing – for example, horses may overgraze the short parts of a pasture even when taller grass is still available.
Livestock grazing comparison units are used by many governments to measure and control the intensity of farming. For example, until 2004 the UK Government had an extensification scheme which paid additional subsidy to farmers who kept their livestock at less than an average of 1.4 LUs per hectare.
Although different schemes have similar aims, they vary in complexity and detail. For example, some schemes give no value to a young calf, but an additional value to a cow together with her calf at foot. Some give values to different-sized animals of the same species, or different values to the same species in different regions. Most schemes use a calculation based on the weight of the animal. Some use figures for animals of different sizes which are directly proportional to their weight – for example the 2006 UK Government scheme uses a figure for ruminants of the animal's weight (in kilogrammes) divided by 650. Others include an adjustment for the proportionally higher metabolic rate of smaller animals, according to Kleiber's law, which states that the metabolic rate of most animals varies according to their weight raised to the power of approximately 0.75. For example, the Food and Agriculture Organization's Tropical Livestock Unit is based on the weight of the animal raised to the power of 0.75, compared with the equivalent figure for a "tropical cow" of 250 kg (550 lb).
The following is a summary of some schemes in common use, using the most closely comparable categories:
|Unit||Livestock Unit: UK government 2006 ||Livestock Unit: The John Nix Farm Management Pocketbook||Animal unit||FAO Livestock Unit (North America)||FAO Livestock Unit (Sub-Saharan Africa)||Tropical Livestock Unit (Unité Bovin Tropical)||Unité de Gros Bétail, Livestock Unit||Dry Sheep Equivalent||Ewe Equivalent, Stock Unit or Livestock Unit|
|Abbreviation||LU, LSU||LU, LSU||AU||TLU, UBT||UGB, LU||DSE||EE, LSU|
|Region||UK||UK||US||North America||Sub-Saharan Africa||Tropics||Europe||Australia||New Zealand|
|Unit equivalent to||Dairy cow||Dairy cow||Beef cow||Tropical cow||Dairy cow producing 3,000 l (790 US gal) milk||2-year-old dry Merino sheep||Ewe with one lamb|
|Weight equivalent of one unit||650 kg (1,430 lb)||455 kg (1,003 lb)||250 kg (550 lb)||600 kg (1,300 lb)||45 kg (99 lb)||55 kg (121 lb)|
|Dry medium beef cow||0.70||0.75||1.00||1.00||0.50||0.80||8.0||6.3|
|Medium beef cow suckling||0.90||0.80||1.00||0.50||18.0|
|Calf under 6 months||0.00||0.34||0.10||0.0||2.5|
|Cow and unweaned calf||0.90||1.14||0.90||18.0||8.8|
|Heifer or steer under 1 year||0.60||0.34||0.30||10.0|
|Heifer or steer under 2 years||0.60||0.65||0.80||0.40||12.0||4.5|
|Heifer or steer over 2 years||0.70||0.80||0.60||9.0||6.0|
- Cattle Scheme Literature: Notes for Guidance 2003, UK Rural Payments Agency, 2003 (pp 11 & 25)
- Chesterton, Chris, Revised Calculation of Livestock Units for Higher Level Stewardship Agreements, Technical Advice Note 33 (Second edition), Rural Development Service, 2006[dead link] (Table figures for unlisted ruminants calculated from weights given in relevant Wikipedia articles)
- FAO paper about Tropical Livestock Units
- Nix, J. 2009. Farm Management Pocketbook. 39th Ed. Corby: The Andersons Centre.
- Jasper Womach, Report for Congress: Agriculture: A Glossary of Terms, Programs, and Laws, 2005 Edition 
- P Chilonda and J Otte, Indicators to monitor trends in livestock production at national, regional and international levels, Livestock Research for Rural Development, 18 (8), 2006, Article #117
- Compendium of Agricultural-Environmental Indicators, Annexe 2: Definitions, Food and Agriculture Organization of the United Nations (includes different values for various regions)
- Coefficients de conversion des animaux en unités de gros bétail (French): Conversion factors for livestock units.
- La Commission Européen: Agriculture et Environnement (French) European Commission, Agriculture and Environment (English version).
- McLaren, Colin, Agriculture Note AG0590: Dry sheep equivalents for comparing different classes of livestock, State of Victoria, Department of Primary Industries, 1997.
- Cornforth, I S and Sinclair, A G, Fertiliser Recommendations for Pastures and Crops in New Zealand, 2nd Ed (New Zealand Ministry of Agriculture, Wellington, New Zealand, 1984), quoted in A History of the Stock Unit System, New Zealand Ministry of Agriculture
- New Zealand Livestock Units on Ruralfind
- Horse stocking rates in Dry Sheep Equivalents
- McGregor, Bruce, Agriculture Note AG0998: A Guide to the Grazing Requirements of Fibre and Meat Goats, State of Victoria, Department of Primary Industries, 2007