Livestock Update, December 2001
Scott Greiner, Extension Animal Scientist, Beef, VA Tech
Part 3: Carcass and Maternal Traits
With increased focus on carcass traits in today's beef breeding programs, the logical question arises- how does selection for carcass merit affect maternal traits? Specifically, does selection for improved carcass characteristics result in undesirable correlated responses in important maternal traits? Unfortunately, few selection experiments have been conducted that directly address this very relevant question. However, work conducted at the U.S. Meat Animal Research Station through the breed germ plasm evaluation studies has provided some insight to the carcass trait vs. maternal issue.
The following tables outline important genetic correlations between selected carcass measures and maternal traits. Both studies were conducted at the Meat Animal Research Center in Nebraska, and include a variety of breeds and crosses. The study conducted by MacNeil et al. (1988) evaluated the genetic relationship between fat trim weight and total retail product weight of steers and maternal traits of their female herdmates. All genetic correlation estimates for fat trim weight were antagonistic with female traits. Thus, selection for reduced fat trim (i.e. improved retail product % and yield grade) would be associated with a correlated increase in age at puberty, increased weight at puberty, reduced fertility, larger mature size, and more calving difficulty in females. Similarly, selection for enhance retail product weight (more saleable product) was found to have an undesirable genetic relationship with the female traits of age at puberty, weight at puberty, mature weight, and calving difficulty. Genetic correlations reported by Splan et al. (1998) also indicate that selection for decreased fat (fat thickness, carcass % fat, and retail product %) would negatively affect fertility (calving rate) and maternal calving difficulty. In these same studies, neither ribeye area nor marbling was negatively associated with calving rate or calving difficulty. Thus, it appears the undesirable associations between maternal traits and carcass merit are mediated through fat thickness.
Genetic Correlations for Maternal Traits with Carcass Fat and Retail Product Weight
|Female Trait||Fat Trim Wt.||Retail Prod. Wt.|
|Age at Puberty||- .29||+ .30|
|Weight at Puberty||- .31||+ .08|
|Conceptions/service||+ .21||+ .28|
|Mature Wt.||- .09||+ .25|
|Calving Difficulty||- .36||- .02|
Genetic Correlations Between Carcass Traits and Selected Maternal Traits
|Calving Rate||Calving Difficulty|
|Fat Th.||+ .19||- .14|
|Fat %||+ .18||- .23|
|REA||+ .15||- .04|
|Retail Product %||- .13||+ .18|
|Marbling||- .05||- .09|
These genetic antagonisms present great challenges to beef producers. Traits such as age at puberty, fertility, mature size, and calving ease all contribute significantly to the economic viability of the cowherd. At the same time, we are challenged to produce a high quality, consistent end product with consumer appeal. Due to the unfavorable correlations between these maternal traits and carcass measures, these goals tend to be in contrast to each other. Further troubling selection for a proper balance between maternal and carcass traits is the general lack of genetic predictors (EPDs) for important maternal traits such as fertility. Hence, tools are less readily available to select for simultaneous optimums in the cow herd as well as end product traits. This leads to the question: Can we genetically design a low-cost female that is adaptable and low-cost in our environment, while at the same time produce cattle that have carcass merit attributes desired by our customers?
In this series, genetic relationships that influence selection have been discussed. The major genetic antagonisms that exist include those between:
The difficulty becomes simultaneously making genetic improvement in these important traits. To do so successfully, several tools for genetic improvement need to be considered:
In summary, the number of economically important traits involved in beef production coupled with the unfavorable relationships that exist between many of these traits make multiple trait selection in beef cattle challenging. Proper use of existing tools such as crossbreeding and EPDs are necessary to optimize performance in multiple traits. Future development of genetic predictors for traits such as reproduction and efficiency, as well as the application of selection indexes for specific production and marketing systems, will enhance our ability to overcome these challenges.