Genetic Improvement: EPDs in the Big Picture
The recent release of a new set of expected progeny differences (EPD) from a greatly expanded ARI performance database has generated considerable excitement amongst alpaca breeders. For some, the excitement comes from having observed the rapid genetic progress this technology has brought to other livestock industries and for some the excitement arises from a bit of trepidation arising from not fully understanding how EPD might fit into their alpaca breeding program.
From a broad perspective, there are four factors that determine how fast we can make genetic progress in our herd. No matter whether we are trying to improve fiber diameter, fleece weight, or spin fineness, those factors are the same. The four factors are selection intensity, accuracy of selection, generation interval, and genetic variability. The first three, we as breeders can control to some extent while the last one is not something over which we have much influence without additions to the genetic pool. I want to discuss the three factors over which we do have some control.
In our hypothetical breeding program, selection intensity refers to how “choosy” we are at selecting animals to use in our breeding program. Are they in the top 10% of animals for fiber diameter or are they in the top 50%? That “choosiness” is one factor that determines how fast we can genetically change fiber diameter with the rule being the more selective we are in choosing animals, the more rapid genetic progress we will make for the traits we are trying to improve.
The second factor, accuracy, also influences how rapidly you can improve any trait. Higher accuracy is associated with more rapid genetic progress. This is the primary reason that using EPD (if they are available for the traits you are interested in) maximizes your rate of genetic progress—EPD are calculated using all available performance data no matter whether it is on the individual, on its relatives, or on its progeny. As a general rule a single observation on an individual with no progeny results in a relatively low accuracy EPD. After an animal produces progeny upon whom data is also collected, the accuracy of the EPD increases. As a general rule of thumb, the more accurate selection decisions are the faster the rate of progress in the trait upon which selection decisions are made. For instance, if you base your selection decisions on fiber diameter, more accurate selection results in faster improvement of fiber diameter.
The final factor we as breeders have some control over is the generation interval or how fast we put new, young animals in our herds. Put another way, it is the replacement rate in our herd. As a general rule, the greater proportion of young, superior, replacements that are put in the herd, the faster the rate of genetic progress. Practically, there are trade-offs associated with putting many young animals back into the herd. First, young animals with no progeny have lower accuracy EPD compared to older animals that have already produced progeny. So it is hard to use younger animals, decreasing our generation interval while also increasing our accuracy of selection.
While we have control over three of the four factors that influence the rate of genetic improvement; this new tools, EPD, primarily improve 2 of these factors that determine rate of genetic progress: accuracy of selection and selection intensity. EPD leverage data on all animals in a population, accounting for relationships amongst animals and for differences in the way animals are raised and managed, this ability increases your ability to accurately select the superior breeding animals. Selection intensity is also increased because of the ability of EPD to account for those managerial and environmental differences between farms and ranches. This ability to fairly compare the genetic potential of animals from diverse environments expands the population from which you can choose replacement breeding animals thereby increasing selection intensity and speeding the rate of progress in the traits of interest.
As you contemplate the next round of breeding decisions, make sure to consider the value of using EPD to speed the rate at which you produce superior animals from your breeding program. EPD can influence both the selection intensity and accuracy of selection, thereby improving your rates of genetic improvement in your herd.