IMPACT OF CHANGES IN GENETIC-IMPROVEMENT PROGRAMS AND ANNUAL CYCLES ON HOLSTEIN SERVICE SIRE MERIT

Monthly averages of Holstein service sire PD from January 1960 through December 1985 were examined to determine if a relationship existed with changes in evaluation methodology. Monthly average of service sire PD for registered cows from January 1971 through December 1985 suggested three linear periods of increase. Regression of PD on sequential month were significantly different for periods defined by hypothesized points of rate change (January to February 1975 and February to March 1984). Rate change points determined from data corresponded reasonably well to times of methodology changes, which can be attributed to new evaluations and accompanying educational programs. Changes in service sire PD by calendar month also were studied. After adjustment for general trend, PD for service sires of registered cows were slightly lower in December and January and about 20 kg lower in June and July than for the highest months. The unexpected bimodal oscillation was nearly the same as for percentage of services that were AI. Apparently, less AI is used in the 2 mo preceding availability of semiannual sire evaluations and in summer months. For a typical 100-cow herd, a dairy producer annually would sacrifice $121 in gross sales, because AI usage was less than in the highest month, February, and $1381 because AI was not used exclusively. Corresponding amounts for the nation would be $12.3 million and $140.9 million. © 1990, American Dairy Science Association. All rights reserved.