What are EPDs?

This technology -- called Estimated Progeny Differences, or sometimes called Estimated Transmitting Ability -- has been used extensively in the beef cattle, dairy, swine, poultry and sheep industries for many years, and is only now being implemented in the alpaca industry. The important points here are that we don’t have to reinvent the wheel and we don’t have to wonder if this technology actually works. Breeders use these EPDs to guide them in their selection and genetic improvement programs. If implemented, an alpaca breeder receives reports on the genetic values for every animal in their herd, based on the performances of those animals and all the animals that are genetically related to them, over many years and management systems. The breeder then uses these EPDs to increase their Selection Accuracy and make the best mating decisions for the goals of their own specific breeding program and thus substantially improve their rate of genetic gain towards those goals.

EPDs allow a breeder to rank all the animals in the herd by genetic value, identify the animals that will be most predictable at producing the desired results in the next generation, and to decide which animals to sell to their customers based on the customers breeding goals.

Estimated breeding value, EBV, is a way of estimating the genetic value of a parent. However, we often prefer to think of what will the effect of using this particular parent be on the offspring. In other words, how much better than average will Mr. Studly’s offspring be for a particular trait. This is referred to as the Estimated Progeny Difference (EPD) or some geneticists use the term Estimated Transmitting Ability (ETA). Since each parent can only contribute ½ of its genes to the offspring, then on average that parent only passes on ½ of its breeding value to the offspring. So one half of the parents breeding value is the estimated progeny difference.

How will we figure out EPDs?

Alpaca breeders keep records on the performance values for polygenic traits that are important to the viability and value of their animals (weights, fiber characteristics, etc) and will enter all this information into a software application that could be added to ARI’s current system. The ARI computer then identifies the genetic linkages between these animals and across years -- like when sires are sold or traded, or when progeny are distributed into many other herds -- and puts this data into one massive calculation for all of the alpacas in the network. This calculation will vary based on the traits that are determined to be important by alpaca breeders to determine the EPD. As time progresses, this database of traits will begin to include all the data from previous years, for all the relatives, across all generations. The EPD calculations even include data from related traits, because an animal's performance in any trait gives information on how it will perform in a similar trait (for example, a good preweaning weight for a fast-growing cria suggests it will also have a good postweaning weight). Each EPD for each animal is recalculated annually once the new data from each new year’s crias, fleece measurements, etc. are entered into the system. Therefore, an alpaca’s EPD could change over time as more data is gained on the alpacas in its pedigree.

What do EPDs look like?

EPDs are given in the normal units of a trait. For example +0.8 pounds (for weights) or perhaps -0.3 microns (for fiber diameter). We must understand that an EPD value is not a ratio or an index. EPDs are expressed as differences (+ or -) from the population mean. Thus, EPDs are always reported as a positive (+) or negative (-) number.

The positive or negative symbols d not necessarily always mean better or worse -- it depends on the trait. For example, a Fleece Weight EPD of +0.7 pounds is good (i.e. more fleece produced at shearing), but an Average Fiber Diameter EPD of -0.5 microns would also be good (i.e. smaller diameter fiber, which is more valuable to fine fiber users).

We can then compare alpacas with positive and negative EPDs, or we can use EPD values to compare animals who both have positive EPDs. For example, a sire with a Fleece Weight EPD of +1.0 lb is good, but a different sire with a Fleece Weight EPD of +2.0 lbs is better. (Assuming of course that we want the offspring to produce more fleece than the parents). EPDs are a new concept to most alpaca breeders, but once you get used to them, they give the most objective and reliable estimation of genetic value possible.