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Selection Indexes for Beef Cattle



There are many traits of economic importance to the commercial cattle breeder. Profitability is related to herds with a high level of fertility, calf survival, and cow longevity as it maximizes calf numbers for sale and minimizes cow culling and replacement cost. Additionally, cow size and milk production are important affecting both feed expense, stocking rates, as well as calf weaning weight and associated revenue. In addition to weaning weight, post weaning gain and efficiency as well as carcass attributes affect the market value of calves sold as feeders and profitability of calve fed to finish. Carcass value is determined largely by factors affecting quality grade as marbling and yield grade as fat thickness, ribeye area muscling as well as carcass weight.

Therefore genetic evaluations have progressed to include many traits for which data bases of animal records are obtained to a point of individuals having genetic values for a dozen or more traits. The genetic estimates expressed as EPDs for such an array of traits are the best tools available for selection, but the amount of information can be overwhelming if not unmanageable. In general breeders determine (usually by intuition) which traits will likely be most beneficial to their bottom line or if there is a particular problem to be fixed. Then it’s a balancing act to settle on traits of emphasis, set some genetic targets, or minimum/maximum levels acceptable.

The development and release of generalized selection indexes by breeds associations represents a simpler and easier way to multi trait select animals by accounting for traits of economic importance from either a cost or revenue basis. An index provides a composite value for the individual by combining relevant EPDs with assumed economics of production. More specifically an index is defined as a combination and weighting of multiple traits and their relative economic impact into one value that can be used to rank animals. They are generally expressed as dollars per head and can be used to compare sires in simple to understand dollar or profit differences associated with progeny in a particular production scenario. Breeds computing and publishing index values provide both maternal or all purpose and terminal or feedlot indexes.

Maternal or weaning indexes are focused on cow-calf producer’s needs and assume replacements will be retained. The America Angus Association Weaned Calf Value includes EPDs that impact four primary economic factors. Birth weight is included for its relationship to dystocia, calf losses and resulting revenues. Weaning weight and milk are included for their impact on pre-weaning calf growth and calf weight for sale and to costs related to lactation. Mature cow size also contributes for its effect on cow energy maintenance as an expense or cost adjustment. The American Simmental Association All Purpose Index includes emphasis on maternal traits including stayability along with some additional post weaning and carcass traits under the assumption heifers not held for replacement and steers, will be fed to finish and sold on a grade and yield basis.

A number of breeds also calculate what might be called terminal indexes. They are designed to simultaneously select for a combination of feedlot and carcass merit. They are useful in comparing and ranking sires for profitability of progeny post weaning.  The American Angus Association Beef Value uses growth and carcass grade and yield attributes EPD’s along with assumed feeding costs and a grid schedule of carcass premiums and discounts to produce a single value representing the average dollar-per-head difference in progeny feeding profitability for sire comparison. The American Simmental Association Terminal Index is designed for evaluating sires where sires are bred to cows with all offspring placed in the feedlot and sold on a carcass merit basis. While material traits are not included, direct calving ease is considered along with growth and carcass traits.

A number of other breed associations also publish a variety of indexes. Each is developed to include economically relevant traits available to account for revenues and costs associated with some defined breeding situation or objective. As generalized indexes, most are based on some assumed market factors and costs which may not be completely appropriate or accurate for everyone’s production situation. As an evolution from these first indexes, we will see computer applications which allow some customizing of indexes or decision support software applications which assist producers in fine tuning multi-trial selection based on their specific costs and markets.

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