An objective and accountable method is needed for deducing the number of registered animals in a breed from registration data. By following the principle that individual breeders register sufficient young females to be certain of having enough replacements for their current breeding stock, the ratios were calculated of the number of adult females in a breed to the number of female registrations, in a given year. Number of breeds considered were 8 cattle, 16 sheep, 8 pigs, 1 goat and 2 equines, all in the United Kingdom or Ireland. This yielded multipliers (4.4 for cattle, 3.3 for sheep, 3.1 for pigs, with confidence limits; and a point estimate of 5.2 for goats) enabling total adult female population to be predicted from a single year's registration data. There was considerable variation between breeds in values of the multiplier, apparently for reasons of breed history and function. This was particularly evident for equines where the two breeds yielded multipliers of 3.8 and 13.9. Multipliers, using registration data that are already in the public domain, can provide an estimate of breed numerical size, which a breed society can either accept or replace with an audited census.
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