The Average ages of Cows and Bulls in Six Breeds of Cattle

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Abstract
From the herd book records of six leading breeds of cattle in Great Britain (Shorthorn, Aberdeen-Angus, Hereford, Ayrshire, Jersey and British Friesian) the ages of the parents of 2618 pedigree calves born in 1925 were tabulated. The average age of cows at calving is found to be 5·722 years ± 0·04, with a standard deviation of 2·816. In four dairy breeds the average age is 5·485 years ± 0·05, while for the three beef breeds it is 6·022 ± 0·05. The “annual replacement percentage” is the number of heifers drafted annually into a herd or breed as first calvers expressed as a percentage of the total number of actively producing cows in the herd or breed. It is in effect the number required annually to make good the losses, and can be calculated from the average age of the cows at calving. This is found to be at least 27 per cent. and agrees substantially with the work of other investigators.

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