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Abstract
Extract
In New Zealand dairy cattle, the average gestation length is commonly accepted as 282 days. This is slightly longer than that reported in European and American studies of Jersey and Holstein or Friesian cattle (Anderson and Plum, Citation1965; O'Conner et al., Citation1968). A feature of these reports and previous New Zealand studies is the differing variation associated with the mean gestation lengths. Part of this may be due to sex, season, breed of sire, age of dam and unspecified herd effects, but is largely the result of excluding or including abnormal gestation periods. The criteria for determining normality have been rather arbitrary in most cases. Abnormally short and long gestation periods may result from disease or from incomplete data recording for conception dates.