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The comparison of two methods of evaluating inheritance of milk production of dairy sires

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  • The production records used were all converted to a comparable based, 305 day lactation period, two times a day milking, and mature equivalent (305 days-2-x-ME) of 71 cows from four Holstein bulls and 59 cows from four Jersey bulls were used for the study. The Equal Parent Index, Regression Index and Herd-Mate Average were calculated for each of eight bulls using five daughters and using all daughters. The study consisted of data collected from 1957 to 1965 in Oregon State University dairy herd. The use of records from five randomly selected daughters gave as good an estimate as was obtained when the records of all daughters were used for indexing dairy bulls. In comparison between the Regression Index and Herd-Mate Average, neither method gave a clear-cut estimate; the Regression Index tended to give an overestimate while the Herd-Mate Average tended to give an underestimate of a bull's transmitting ability. All indexes except the Herd-Mate Average for Holstein bulls failed to give an accurate estimate of the average actual production of the daughters. There was a significant difference between the Holsteins and Jerseys for both milk and butterfat production. Also, the three methods differed significantly from one another in the estimates of transmitting ability of sires.
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