Expected Progeny Differences: A New Tool for Breeders

The first time a person specifically chose two animals to mate in the hopes of producing a better offspring is lost to history. Likely that person was trying to produce a faster horse or camel that would bring them the prestige or wealth associated with winning races. Over time our ability to select the best animals for a breeding program and our knowledge of inheritance and genetics has greatly improved. Today in the beef, dairy, pig, and sheep industries, the most widely used technology for the selection of breeding animals are expected progeny differences (EPD). Breeders of the species have used EPDs to make rapid and marked genetic improvement in numerous traits. In Europe, equine breeders have begun using EPDs to make genetic improvement in a variety of performance traits as well. Over all of these species, EPDs have proven time and again to be the most accurate method of selection of breeding animals and, with appropriate use, to result in rapid rates of genetic change.

Remember, EPDs are predictions about an animal’s genetic merit for a specific trait and how their progeny should perform for those traits. EPDs are calculated using pedigree information, including relationships amongst all animals in a population, and trait performance data (e.g. fiber diameter, fleece weight, etc.) on those animals.

While the application of this technology is relatively new to the alpaca industry, it has been in use in the other livestock industries for over 30 years. The statistical theory behind the BLUP (best linear unbiased prediction) methodology used to calculate EPDs was originally developed in the early 1960’s. However the computer technology/capability was not available at that time to implement the technology on a large scale. In the 1970’s computing technology began to catch up with genetic evaluation theory and the ability to calculate EPDs on a large scale became possible. Originally EPDs were calculated for sires only, however since that time further statistical and computing technology advances have resulted in the ability to calculate EPDs for all animals in large populations. For instance, the Colorado State University Center for Genetic Evaluation of Livestock services more than 20 different beef cattle breeding organizations in the U.S. and abroad with the largest database used to calculate EPDs for over 2.7 million animals.

As with any “new” technology, when EPDs were first adopted in beef and dairy industries there was considerable skepticism and opposition voiced by some breeders. They questioned the effectiveness and some thought EPDs took the “art” out of animal breeding. These skeptics were a valuable part of the process, as that skepticism led to studies designed to validate the usefulness of the tool. Since the original release of EPDs in the beef and dairy industries, there have been numerous scientific studies to evaluate whether EPDs work in the field. Repeatedly these studies have shown EPDs to be an extremely effective selection tool for making genetic change in animal populations. On the other side, the “art” of breeding is still intact, because on an individual animal basis, EPDs can change as additional data becomes available and sometimes an animal expected to be outstanding proves not to be such, or conversely an animal expected to be a marginal performer is proven to be outstanding.

To fully understand why EPDs are such an excellent tool for making genetic change, one needs to understand the factors that influence how rapidly genetic progress can be made in your herd. Genetic improvement in any trait is a function of four factors which include: the generation interval of your breeding program, the selection intensity, accuracy of selection, and the genetic variability in the breeding population. Generation interval is the average age of breeding animals in the herd when progeny are produced. The more superior young stock put into your breeding program, which lowers the average age of your herd, the faster the rate of genetic change. Selection intensity is how selective or “choosy” you are in selecting new replacement animals to enter your breeding program. The more selective, the more rapid the genetic progress you will make in your breeding program. Accuracy of selection is how well you choose the superior animals for breeding and is a function of the amount of performance data on animals and their relatives. The more accurate you are, the faster the rate of genetic progress. I am certain, that most of us have selected animals to use in a breeding program that eventually produced progeny who performed considerably more poorly than we had hoped for. My accuracy of selection was poor in those cases. Accuracy reflects that ability to select the “best” animals. Finally, the underlying genetic variability in a population also effects the rate at which genetic progress can be made but there is little breeders can do to influence genetic variability.

Of those four factors, EPDs act favorably on two of those factors: accuracy and selection intensity. Because EPDs account for relationships amongst all available performance data on all animals in the database, accuracy of selection is higher, which results in faster rates of genetic change. Selection intensity is also improved with EPDs. At first this may be confusing, but in essence the pool of animals from which to select animals has expanded. EPDs allow fair comparison of potential animals from multiple herds. We all know there are management and environment differences between breeders and locations. Often, just by being better managers and having a better nutritional program, an animal may look better than those of a sub-par manager, even though it may not be genetically superior. EPDs account for these differences and thereby expand the pool for selection. This is one of the reasons EPDs are so widely used in the other livestock species — it gives breeders the ability to compare animals on a genetic level, factoring out environmental differences.

EPDs have been adopted by breeding industries outside of livestock as well. In recent years, EPDs have been used to select breeding animals for the assistance dog industry. The goal obviously is to produce dogs that are better suited to providing assistance to the disabled and others in need.

EPDs have been widely adopted in both the livestock and non-livestock industries and for good reason — EPDs result in rapid genetic improvement in those animal populations. The beef cattle breed associations continually examine how their animals have genetically changed over time with the outcomes of EPD calculations and subsequently publish these trends to their members. Graphs of these genetic trends for most breeds show rapid improvement after EPDs were adopted. The dairy industry shows similar improvement. Today’s dairy industry produces more milk from fewer cows than ever before, much of which is due to genetic improvement in that industry. To say the least, EPDs work! It is an exciting time for alpaca breeders as this technology becomes more widely used.