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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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