Combined value ($C), expressed in dollars per head, includes all 15 traits involved in $M and $B.
The breeding objective, which drives the $C model, is built around a 500 head commercial cowherd
that replaces 20% of their breeding females per year with replacement heifers retained within their
own herd. In addition, this same herd then retains ownership on these cull heifers and their steer
mates through the feedlot and market those cattle on a quality-based carcass merit grid. Expected
progeny differences (EPDs) directly influencing a combined index: calving ease direct (CED) and
maternal (CEM), weaning weight (WW), yearling weight (YW), maternal milk (Milk), heifer pregnancy
(HP), docility (DOC), mature cow weight (MW), foot angle (Angle), claw set (Claw), dry matter intake
(DMI), marbling (Marb), carcass weight (CW), ribeye area (RE) and fat thickness (Fat).
$C is a linear combination of $M and $B. The simple formula to calculate $C on any animal is $C = $M + (1.297*$B).
In the example below, Bull A and Bull B are compared head-to-head. As a result, Bull A and Bull B should produce
progeny with similar profitability if heifers are being retained as replacements and remaining calves are fed and
marketed on a carcass merit grid.
||$M + (1.297*$B)
||70 + (1.297*127)
||51 + (1.297*140)
The idea of combining maternal and terminal traits into one economic selection index allows
a producer to make genetic progress in several different traits at once while accounting for
the relationships among these traits which may pull costs and revenues in different directions.
For example, continuing to increase WW, YW and CWT results in more saleable product, increasing
revenue; however, it also drives up input costs across other segments of the operation. Mature
cow size, for instance, is positively correlated to these three growth traits. As increased
selection pressure on weaning, yearling and carcass weight continues, mature cow size will
increase resulting in higher maintenance energy requirements increasing costs. $C recognizes
these types of relationships and targets optimal level of genetic change in each of these
traits that results in maximum profitability.