by: Dr. Lisa Kriese-Anderson
Extension Animal Scientist Auburn University
Selecting beef cattle based on expected progeny difference (EPD) values provides the most accurate selection method currently available to beef producers for economically important traits. EPD values predict on average how future progeny of each animal are expected to perform relative to the progeny of other animals. It cannot be over emphasized that EPD values must be combined with visual appraisal for structural correctness, muscling and overall eye appeal when making herd selection decisions.
For most Alabama commercial cattle producers, pounds of weaned calf are the market product. These calves, once sold, gain additional weight on forages before going to a feedyard or head directly to a feedyard for finishing. For those cattle producers selling all calves at weaning or yearling, EPD values to concentrate on include calving ease, birth weight, weaning weight, perhaps yearling weight and carcass traits.
EPD values do not predict actual performance. They predict differences in performance because actual weights and measures are controlled not only by genetics, but also the environment. A calf will weigh more raised in an excellent environment compared to a calf raised in a poor environment. Looking at the information in Table 1, several pieces of information can be analyzed.
Calving ease is the best EPD value to use to predict whether calving problems will arise. Calving ease EPD values indicate the percentage of progeny unassisted births from first calf heifers compared to another animal or the breed average. From the data in Table 1, Bull A's progeny will be born unassisted 10 percent more than bull B's progeny from first calf heifers. Additionally, Bull A's progeny will be born six percent more unassisted compared to all other animals of this breed born in 2015.
Birth weight EPD values can also be used to predict calving difficulties in first calf heifers. However, birth weight is only an indicator trait. Birth weight does not provide the percentage of calving problems or percentage of unassisted births from first calf heifers. In this case, Bull A's progeny will weigh two pounds less at birth than the progeny of Bull B. Again, EPD values do not predict actual birth weight. Birth weight is not only determined by genetics, but also the breed of the dam, whether the calf is born to a first calf heifer, the time of year the calf is born, the sex of the calf or whether the calf is an embryo transfer calf or a natural calf. From the information in Table 1, progeny of Bull A will weigh slightly less than the breed average, while progeny from Bull B weigh one pound more. Using calving ease EPD values are much more useful in determining whether a bull should be used on first calf heifers to prevent calving difficulty.
Weaning weight is what most cattle producers are paid for. In this example, progeny from Bull B will weigh nine pounds more at weaning than progeny from Bull A. Calves produced from Bull A will be comparable to all calves born from animals born in 2015, while progeny from Bull B will be eight pounds heavier than all other animals born of this breed in 2015. Multiplying additional pounds by market price per pound will give an indication of the economic impact selection decisions based on EPD values will produce.
Actual weaning weights depend on the farm environment. The primary factor for differences in actual weaning weights on farms is available nutrition for both the cow and the calf. Those animals with access to adequate and appropriate nutrition will be able to express their genetic potential more so than animals raised under limited nutrition. Herd health will also play a factor, especially respiratory disease and parasite loads. Producers who also administer growth implants to calves according to label recommendations will also see boosts in actual weaning weights with adequate available nutrition.
Accuracy indicates how much information was available to predict the animal's genetic value. Accuracy values range from 0 to 1. EPD values with an accuracy level close to one predict the true genetic value of that individual very well. Accuracy values can be thought of as a level of risk. As animals get older and produce more progeny with performance records, accuracy values increase. Most young bulls will have accuracy values between 0.25 and 0.45.
Rank indicates how the animal genetically stacks up in the breed. Bull A is in the top 15 percent of the breed born in 2015 for calving ease, slightly above average, where average is 50 percent, for birth weight and slightly below average (52 percent) for weaning weight. Bull B is in the bottom 20 percent of the breed born in 2015 for calving ease, bottom 10 percent of the breed for birth weight and top 20 percent of the breed for weaning weight. Both Bull A and Bull B have a place in the beef industry. Most likely, Bull A would be used on first calf heifers to minimize calving difficulties while still producing adequate pounds at weaning. Bull B most likely would be used on mature cows and produce fairly heavy calves at weaning.
When keeping replacement heifers, at least two additional EPD values need to be considered. These EPD values are maternal calving ease and milk or maternal milk. Maternal calving ease EPD values predict the calving ease of daughters. Milk or maternal milk EPD values predict the added pounds of weaning weight of a daughter's calf due to her ability to milk.
Many producers have felt the need to use bulls with maximum or very high EPD values for growth, milk and carcass traits while minimizing birth weight EPD values. If the environment is not good enough, differences in performance probably will not be seen. For many, a moderate or breed average approach may be best.
Replacement females with higher milk or maternal milk EPD values will have increased maintenance energy requirements. The maintenance energy requirement does not just increase during lactation, but for 365 days/year. Thus, cows with higher milk production will have higher feed requirements. Again, match the genetics with the environment. Many of our southern forages do not have high enough protein or energy value to support moderately high or high milk EPD values without supplementation.
Almost all U.S. Beef Breed Associations have EPD values for calving ease, birth, weaning and yearling weight, milk or maternal milk, maternal calving ease and carcass traits. Some breed associations also have EPD indexes. EPD indexes combine EPD values along with economic weights to create a simplified selection tool for commercial breed producers. However, all EPD indexes are breed specific. Another important note is EPD values cannot be compared across breeds. They are only valid within a specific breed unless across breed EPD adjustment factors are used.
Effective use of EPD values within a herd depends on remembering three concepts.
1. Use EPD values that are relevant to your production system. For example, there is no need to worry about milk or maternal milk EPD values if replacement heifers are not retained.
2. Match the EPD values with the environment. Do not purchase or create genetics that your environment can not maintain without the addition of significantly more feed inputs.
3. EPD values are the best and more accurate genetic tool available to predict the future performance of progeny.
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