Use of Bimonthly Records in Herd Testing

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Abstract
One objective of herd improvement work is to reduce the cost of herd-testing and one possible method of achieving this is to test cows in alternate months instead of every month. This paper reports comparisons of bimonthly records (obtained from herd-testing in alternate months) with monthly records (lactation figures obtained from monthly herd-testing) in a study involving 35 herds. Comparison of herd averages, within-herd ranking of cows and repeatability of records under the 2 systems indicate that bimonthly records are suitable for within-herd comparisons but not for between-herd comparisons. Within-herd ranking of cows was almost identical and the repeatability of the bimonthly records was only 0.04 lower than that of the monthly records. Sire proofs calculated from the 2 sets of records in these herds ranked the bulls similarly.