After the great feedback on Fridays post which was written by Dr Sara Via on EPDs I have decided to include more of her thoughts on this topic. So here is Sara back by popular demand.

"I got interested in alpacas because I wanted to be able to utilize my training in quantitative genetics (the source of EPDS) in a practical non-academic way.
Just to review, an Expected Progeny Difference EPD is the predicted difference between the average trait value of an individuals progeny and the mean trait value in the group of animals for which the EPDs have been estimated. Estimations involve probabilities, but an estimated progeny difference is far better than a "guess". In the same vein, "expected" is statistical jargon for "predicted using a whole ton of math").

An individual alpaca's EPD for a given trait is estimated using information from all of its relatives.
This means that even a new born cria has an EPD if its relatives have been measured. Using the entire pedigree really speeds things up relative to older methods that only used the progeny. So, it isn't necessary to worry that a stud will be decrepit before his EPD is estimated reliably. Anyway, additional measurements on an individual in the first few years of life, and then on its offspring increase the accuracy of its EPD estimate.
Fortunately, when EPDs are reported they come with an indication of their accuracy, which is important to take into account when making your alpaca breeding decisions.

This post is getting long, but I wanted to comment on two other issues- first, in a perfect
world it would be great to measure everything and calculate alpaca EPDs for conformation traits, birth weights, weight gain and other indices of vigor, as well as for fleece traits. However, the experience in the Ideal Alpaca Community has been that "just"
getting fleece measurements is enough of a challenge to start with. One good thing about the way that the fleece data have been collected is that the measurements are reported to the database directly from Yocum-McColl, which cuts down on errors and on the temptation to just not send in the measurements that aren't what the breeder was hoping for.

Lastly, the purpose of the Studmasters male alpacas in the IAC is not to restrict the group of males used for breeding within the community, but to provide a reference set of excellent studs whose progeny will be found on numerous farms. This is one very important way that the environmental variation that mentioned is handled in EPD estimates. Breeders in the IAC will have many other sires that have produced progeny this year.
The important thing is that all of those alpacas are measured and included in the population for which EPDs are estimated. Then we will see how the Studmasters actually stack up relative to other alpaca males in the group. We probably want to add some additional Studmasters to increase the genetic variability in the reference group (and replace those that are getting old), and these are likely to come from the pool of males that are measured each year." Sara Via
Professor of Biology, University of Maryland Owner, Meadowlark Farm Alpacas
4811 Manor Lane
Ellicott City, MD 21042