Heritability of Rates of Milk Flow and Time Required to Milk

Data on rate of milk flow were collected in the Illinois Crossbreeding experiment on 337 first and second lactations. Estimates of the heritability of maximum rate of flow, initial rate of flow, and two measures of Milking Time 1 and 2 were obtained for each month of lactation and for the average of the first six months by doubling the intra-sire, intra-breed group regressions of daughter on dam. These estimates were obtained on the unadjusted data and on the data after adjusting for the total yield at each milking. Estimates of heritability of .54 .12 and .50 .12 were obtained for maximum rate of flow and initial rate of flow, respectively, from the adjusted data for the average of the first six months of lactation. The estimates of heritability of milking time ranged from .22 ---+ .13 to .27 -4-.14. One would make substantial gains in improving maximum rate of flow by selecting for milk yield on a basis of milk yield alone or on a basis of an index constructed from milk yield and maximum rate of flow.