Genetic parameters of several measures of milk flow rate and milking time.

Heritabilities and genetic correlations of milking rate, time, and yield were estimated by intrasire regression of daughter on dam for 252 Holstein pairs. Heritabilities were: lactation yield, .51 +/- .11; peak rate, .47 +/- .11; bucket milk yield, .38 +/- .10; average rate, .37 +/- .12; milk yield to .45 kg/min, .19 +/- .12; total time, .17 +/- .12; duration of peak rate, .10 +/- .10; strip time, .08 +/- .15; yield during peak rate, .07 +/- .11; and strip yield, .01 +/- .17. The genetic correlation of peak rate with lactation milk yield was .69 +/- .08, indicating substantial genetic improvement in milking rate by selecting for milk production. The genetic correlation between total milking time and lactation milk yield was .50 +/- .20, indicating an increase in total milking time due to selection for milk. Direct selection for peak rate would provide an opportunity to reduce total milking time.