Under this approach, different weights are applied to each trait considered important to dairy producers. Variation in traits is equalized through the application of weights. The numbers representing the weighted traits are added to produce a single number. This number is used to rank the bulls, and the higher ranking bulls are selected as sires. This approach allows strength in an important trait to offset weakness in some other trait and is more efficient than truncation selection.
Index selection is effective, but it has some problems in practical situations.
For instance, the weights often are difficult to establish and may vary from herd to herd. Also, index selection creates operational difficulties because one bull will be best for all dairy producers that have the same priorities. With this approach, each dairy producer establishes herd breeding goals for fat test, overall type, semen price and several individual type traits. The user then selects one of four economically important traits to receive primary emphasis in the selection program. The computer chooses bulls with the specified minimum averages for the fat test and physical type traits and with the specified maximum average semen cost.