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Graphic Method Showing Efficiency of Dairy Bulls

Department of Farm Development, Nevada Agricultural Experiment Station

ABSTRACT

Dairy bulls are commonly evaluated by comparing the yields of daughters and dams. The result is usually expressed as an index which is supposed to represent an estimate of what the production of the bull's daughters would be if they were not influenced by the hereditary effect of their dams.

Such an index is concise and valuable but for educational purposes in classes or farmers' meetings it may be helpful to illustrate the efficiency of bulls by a graphic method such as that used in the accompanying chart.

In this chart the butterfat production of dams and daughters from six different bulls is shown. The records are from a small dairy herd over a period of years.

The graphs are so designed that when the records of a dam and daughter are equal, the dot will fall on the diagonal line; if the daughter's production is greater than the dam's the dot will be above, while if it is less than the dam's it will be beneath the diagonal line.