Genetic Parameters of Five-Month Lactation Records

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Abstract
Genetic parameters of five-month records were estimated from 27,612 records divided into 2 age of freshening groups and 5 breeds from between and within sire group analyses of deviations from herd-mate averages. Heritability estimates of 150-day milk production for first and later lactations were: Ayrshire, .40 and .20; Guernsey, .03 and .14; Holstein, .27 and .10 and .07, and Brown Swiss, .59 and .21. Genetic correlation estimates between 150-day and 305-day milk production of the first and later lactations were: Ayrshire, .95 and .93; Guernsey, .66 and .68; Holstein, .96 and .89; Jersey, .88 and 1.02; and Brown Swiss, .91 and .93. Estimates of the within sire regression of daughter records on herd-mate averages were for 150-day and 305-day first lactation records: Ayrshire, 1.01 and .89; Guernsey, .71 and .72; Holstein, .89 and .88; Jersey, .59 and .56; and Brown Swiss .73 and .80. Similar, although generally slightly higher, regression coefficients were found for later lactation records. The results suggest that differences in persistency and rate of maturity are not likely to be of major importance in evaluating sires on 150-day rather than 305-day daughter performance.