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Selection for carcass merit begins in the bull buying pen

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Published on March 21, 2020

“Consumers want beef that is tender, juicy, flavorful and lean,” states Professor Emeritus and Texas A&M Extension Beef Cattle Specialist Stephen Hammack in an A&M Extension publication.  “The primary indicators of these factors are U.S. Department of Agriculture (USDA) Quality Grade and USDA Yield Grade.” 

            Quality grade predicts eating satisfaction while yield grade predicts percent leanness, or cutability, according to Hammack.

            The publication, produced by AgriLife Communications, The Texas A&M System, and titled Texas Adapted Genetic Strategies for Beef Cattle IX: Selection for Carcass Merit, discusses selection of cattle based on carcass merit. The publication points out one of the first places a producer can start improving their carcass merit is in the bull sale pen when selecting for sires. 

Factors affecting carcass traits

            First and foremost, Hammack points out there are many factors affecting carcass merit. 

            “According to the U.S. Meat Animal Research Center, important factors affecting tenderness include genetics, age, time on feed, feed rations, growth implant programs, animal temperament, pre-slaughter techniques, slaughter procedures, electrical simulation, chilling conditions, calcium chloride injection, blade tenderization and carcass aging time and conditions,” explains Hammack. 

            On top of these, carcass merit may also be improved through selection of carcass traits.

In order to make significant genetic improvements through selection on a carcass trait within a particular breed, Hammack states producers need to select outstanding sires, which is usually accomplished through AI.

            “For the majority of commercial producers who do not use AI, the fastest genetic change can be made by using superior sires from a breed noted for high expression of the specific trait they are looking at,” says Hammack.

            “The greatest benefit usually results from a combination of moderate levels, not extremes, of traits economically important to the producer,” he continues.

Relationships between carcass traits

            In order to better understand how to change carcass merit through genetic selection, Hammack says producers need to have knowledge of genetic influences on carcass traits and how they are related. 

            “Research has shown marbling, ribeye area, fat thickness over the ribeye, cutability and tenderness are all moderately to highly heritable,” states Hammack. “Therefore, improvement should be possible if breeding stock are selected for those traits.” 

             He notes selecting for a specific carcass trait may affect others.

            “Based on documented genetic relationships, selection for reduced fat should have little effect on ribeye area but markedly improve yield grade, although tenderness may be slightly reduced,” states Hammack. 

            “There are conflicting estimates of the genetic relationship between external fat thickness and marbling. Research indicates marbling declines somewhat as external fat is reduced by genetic selection,” he adds. “However, some breed associations have found little genetic relationship between fat thickness and marbling, based on field data collected for developing carcass EPDs.” 

            He continues, “Research also shows if genetic selection is used to increase marbling, it should cause a slight reduction in ribeye area, moderate improvement in tenderness and slightly reduced cutability. However, breed association field data shows little genetic relationship between marbling and cutability.” 

            Hammack also notes selecting for specific carcass traits may affect other important production traits as well. 

            He explains research shows genetic selection for increased marbling will likely reduce weaning weight and yearling weight, while selection for higher cutability will likely increase weaning weight, yearling weight and mature cow weight. 

            He also explains there appears to be little genetic relationship between reproductive factors and marbling, other than the fact that genetic types with more marbling may also reach sexual maturity somewhat earlier.

            “Selection for higher cutability may have negative effects on calving rate and calving ease,” he says. “Selection for extreme muscling appears to affect reproduction adversely in both males and females.” 

Overcoming affects of genetic correlation

            Hammack states it may be possible to overcome the effects of undesirable genetic correlations by concurrently selecting for all of the traits a producer is concerned with. However, he also notes selecting for more traits slows the rate of genetic change and concurrent selection for genetically antagonistic traits slows the rate of change even more. 

            Hammack points out most breed associations have an EPD for carcass weight, some have carcass-derived EPDs for marbling, ribeye area, fat thickness, yield grade and percent retail product and others have EPD for ultrasound measures of ribeye area, fat thickness, retail product and intramuscular fat.

            “Several also have $Value Indexes, which combine carcass and ultrasound measures with economic factors,” he says. “A few also have an EPD for tenderness.”

            Since carcass weights are closely related to yearling weight, ribeye area and fat thickness are included in yield grade and percent retail product and tenderness is important in consumer satisfaction, Hammack says the most useful EPDs in selecting for carcass merit are marbling or ultrasound intramuscular fat, yield grade or percent retail product and $Value carcass indexes. 

            Hannah Bugas is the assistant editor for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.

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