Data management

Herd size and calf/cow ratio

The numbers of calves ≤ 12 months of age, weaners (12-36 months of age), adult males and adult females (≥ 36 months of age) alive on 1st March, 1st June, 1st September and 1st December each year (from 1987 to 1997) were calculated.

The two pairs of months (March and June) and (September and December) were then averaged to give average numbers over the two halves of the year. The numbers of animals in each category were then summed to give a total average herd size for each 6-month period.

The average number of calves alive during each 6-month period was divided by the number of adult females to estimate the average calf/cow ratio. This statistic gives an overall measure of cow reproduction/calf survival.

It was found easier to perform most of the calculations of the 6-month animal averages described in the previous pages in SAS rather than GenStat. However, the REML analyses and the least squares analyses of variance that used the 6-month animal averages as average observational units were done, as has been illustrated, in GenStat.