The majority of that improvement has been due to the implementation and use of expected progeny differences (EPDs).
Since beef producers are paid for their animals on the basis of weight, or in some cases by the merit of animal carcasses, most EPDs found in sire summaries involve growth traits and carcass traits.
There is no disputing the level of importance reproduction has when compared to other traits. Several studies have shown that in commercial beef cow herds, the value of improvements in reproductive traits outweigh the improvements in other traits.
As an example, consider the evaluation of the relative economic weights of various trait categories conducted by the American Gelbvieh Association.
The estimated relative importance of reproductive traits, growth traits and product traits was approximately 4 to 2 to 1, respectively.
To gain some perspective of the economic effect of reproductive performance in beef cattle herds, consider the following example.
The value of a weaned calf per cow exposed when 100 percent of the cows are pregnant is $750 per cow [500 pounds of weaned calf x $1.50 per pound x 100 percent cows pregnant].
When the percentage of pregnant cows drops to 85 percent, then the value of a weaned calf per cow exposed drops to $637.50 [500 pounds of weaned calf x $1.50 per pound x 85 percent cows pregnant].
The loss of $112.50 is due to the poor [85 percent vs. 100 percent cows pregnant] reproductive performance in the herd.
Even though a high level of reproductive performance is vital to a beef operation’s bottom line, selection for reproductive traits has often been overlooked, or not emphasized, when breeding programs are developed.
Recently, Walmart has expressed a desire to place higher-quality (USDA Choice) beef in its retail counters.
As Walmart begins to implement this change and branded programs such as Certified Angus Beef® seek to source cattle, the increased demand for higher-quality beef has resulted in wider USDA Choice-Select spreads.
In November 2011, CattleFax reported a Choice-Select spread of $18 per hundredweight (cwt) and an average carcass weight of 860 pounds.
This results in a price differential of $154.80 between Choice and Select carcasses. CattleFax projects the average Choice-Select spread for 2011 and 2012 to be $7.25 and $9.25, respectively.
As the Choice-Select spread fluctuates around these levels, it seems clear that carcass quality will warrant some consideration as beef producers make their selection decisions.
The examples listed above clearly show that reproductive performance and carcass quality can be categorized as economically important traits in many beef cattle operations.
As beef cattle producers struggle to prioritize the traits to include in their selection strategies, a question often arises – Can we select for carcass quality without adversely affecting reproductive performance?
Historically, there has been little agreement on how reproductive performance should be described, or expressed, and few studies exist that examine the direct relationship between carcass quality (marbling) and reproductive performance.
A couple of studies look at the relationship indirectly. In these studies, daughters of low-marbling sires, high-marbling sires, low-accuracy (marbling EPD) sires, and high-accuracy (marbling EPD) sires were evaluated based on reproductive performance measures.
The measures included age of puberty, age at first calving and calving interval. In each case, the marbling potential or accuracy of the sire’s marbling EPD did not have an effect on the reproductive performance of the daughters.
More recently, Colorado State University researchers conducted a study to estimate the genetic relationships between reproductive traits (heifer pregnancy and scrotal circumference) and carcass quality traits (intramuscular fat and marbling score) in Red Angus cattle.
The heritabilities reported for these traits were moderate (ranging from 0.17 to 0.35), suggesting the traits should respond to selection.
The genetic correlations between the reproductive traits and the carcass traits were low (ranging from 0.01 to 0.13), suggesting there is little (if any) genetic association between the traits. It was concluded that genetic selection for both reproductive traits and carcass traits should not be antagonistic.
These studies suggest that it is possible to select for carcass quality without adversely affecting reproductive performance.
Generally, as beef producers plan and develop their herd’s breeding program or selection strategy, they should accurately identify the traits of economic importance for their particular operation, focus selection efforts on traits with moderate-to- high heritabilities, be aware of trait antagonisms and how they might affect selection response, maintain objectivity when evaluating the selection strategy and set realistic and obtainable goals. 
References omitted due to space but are available upon request.
PHOTO:
Top Right: Studies suggest a possibility to select for carcass quality without adversely affecting reproductive performance. Staff Photo.
J. Benton Glaze, Jr.
Extension Beef
Cattle Specialist
University of Idaho
bglaze@uidaho.edu
