Space allowance for pigs is typically expressed as the number of square metres per animal, with the inverse being the stocking density (the number of animals per square metre). However, without also understanding the age, weight or size of the pigs in question, these units of measure are relatively meaningless (Spoolder et al., 2012). In the early 1980s, Petherick and Baxter (1981) used allometry to establish the static spatial requirements of livestock. Allometry describes the growth relationship between part of an animal and the whole of it, regardless of age and weight (Petherick, 2007). Petherick (1983) introduced an allometric equation that described the relationship between a pigās weight and its linear dimensions. This equation is currently used to calculate the minimum space allowance for growing pigs as follows:
- Space allowance per pig (m2) = k Ć Liveweight(kg)0.67.