A Comparison of Bimonthly and Quarterly Testing with Monthly Testing for Estimating Dairy Cattle Production

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Abstract
Milk and butterfat records for 1255 Holstein-Friesian cows in 42 herds were computed for the first 305 days of lactation. The centering day method and monthly, bimonthly and quarterly tests were used. The bimonthly and quarterly records were compared to the monthly records according to their variability, avg. difference in yield, avg. % error, and frequency of errors larger than [plus or minus] 10%. The results were similar for both milk and butterfat yield. The differences in variability between the monthly, bimonthly and quarterly tests were small. The avg. differences in yield were significant but unimportant. The avg. % errors from milk yield were 3 for the bimonthly records and 5 for the quarterly records. The avg. % errors for fat yield were 4 and 6, respectively, for the 2 methods. The frequency of errors larger than 10% was 1/46 regarding milk yield in bimonthly records and 1/8 in quarterly records. Errors of this size occurred in the butterfat comparisons at the rate of 1/16 bimonthly records, and 1/6 quarterly records. The frequency of the large errors indicates that bimonthly and quarterly records should be satisfactory for sire provings and population studies, but they may be unsatisfactory when used as individual lactation records.

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