Using indexes to guide bull buying decisions

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There has really been an explosion of information available to ranchers to help make genetic decisions. The number of traits for which we have Expected Progeny Differences (EPDs) has increased to include carcass traits as well as traits such as stayability and disposition. All that information doesn’t mean that the task is any easier. It can be a bit like picking your twenty favorite George Strait songs; some hard decisions need to be made.

One of the challenges of using EPDs is balancing between different traits and what kind of trade-offs we can afford to make. Perhaps there are two bulls you’re considering; one offers excellent growth performance and acceptable carcass traits, the other just meets your target for growth, but the bull’s marbling EPD is exceptional. Traditional trait EPDs don’t do a very good job of telling us which one of these two bulls will be more profitable to own. 

EPDs also don’t address costs. We all know that selecting for more growth and more maternal milk in the sires of our replacements can increase our weaning weights. We also know that those higher-producing cows require more nutrients, and that costs money. In that situation, a tool that evaluates the value of the outputs but also considers input costs would be very useful.

Fortunately, those kinds of tools are becoming more available in the form of selection indexes. Selection indexes use the trait EPDs in an economic model to put a dollar value on an individual bull. A listing of the selection indexes currently available can be found in Table 1. For example, the American Angus Association publishes a Weaned Calf Value ($W) index that considers birth weight, weaning weight, maternal milk, and mature cow weight. The model considers how changes in those traits might affect percent calf crop and weaning weights, and also considers what might happen to feed costs over time using real world prices for both cattle and feed.

1Adapted from the Mississippi State University publication: “Expected Progeny Differences and Selection Indices for Beef Cattle Selection.”

We still need to use our common sense when we use these tools. We could have a case where a bull might be undesirable for one trait, but so superior for one or two that he still ranks very high on an index. A rancher might want to set some minimum or maximum values for some traits to make sure that the bull will “fit” in their system.

Also, these indexes are set up using a one-size-fits-all approach that may not exactly fit your situation. Suppose an index assumes that bulls will be used on both heifers and cows. If a ranch is selecting bulls that will only be used on mature cows, that index might place more emphasis on calving ease than would be necessary.

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