Estimated Breeding Values (EBVs) explained
Why have EBVs?
The value of EBVs comes from their use in breeding plans because they help breeders achieve the aims of their breeding plan more quickly and more accurately than might otherwise be achieved for the traits that have EBVs.
The benefits of an EBV system are that the breeding progress is:
EBVs will help breeders make better breeding decisions, identify good and bad alpacas early, and can help with the valuation when buying and selling.
What are EBVs?
EBV stands for estimated breeding value and uses measurements to calculate an estimate of the genetic worth of an alpaca for one or more traits of interest. EBVs can only be calculated for traits that can be measured, like fleece weight and micron diameter, so they always have units like kg or mm. Alongside measurements of the alpaca in question data is used from related alpacas – parents, offspring, aunts and uncles – to help improve the estimate of genetic worth. The more data there is available the better the estimate that can be made.
In the example below the reliability of the estimate is represented by the narrowing blue cone. The true value of the fibre diameter EBV is 17.5 micron but if we only had measures from the individual the EBV might be anywhere between 19 and 15 micron. Using measures from parents as well means the estimate improves, to give a measure between 18 and 16 and if you add in further data from, say, 10 progeny the estimate could narrow to between 17 and 18.
EBVs are recalculated every year to reflect the increased data available. So, for a widely used stud male after a few years there could be 30 or 40 offspring contributing to his EBV and it probably would not move as much as it might when the first few offspring contribute to his EBV calculation.
How do EBVs work?
EBVs uses measures of a trait (for example micron diameter of fibre) and the pedigree (which animal is related to which) to disentangle the effects of genetics and environment. The measurement taken on a particular trait at a particular time is the product of the genes the alpaca has, and the management environment it has experienced (like feed availability and disease challenges), as well as other factors like age, and sex.
One way to think about it is to imagine identical twins separated at birth and exposed to vastly different feeding regimes, one good and one poor. At a year old one twin could conceivably be 50% heavier than the other. The environment has made the difference, but we know they have the same genetic potential for growth because they are identical. So, when it comes to breeding, the quality of offspring from either twin would be expected to be the same and their EBVs would reflect that despite the very different appearance.
The way genes are passed from one generation to the next means that for lots of traits predicting the outcome in the offspring is difficult. For complex traits like micron of fleece this is because there are many genes that to contribute to the quality of fleece produced.
If you mated a male with an EBV of 18 micron to a female with an EBV of 22 micron you might expect the offspring to have an EBV of 20 micron. And that is what happens on average BUT, and it is a big BUT, the possible range of outcomes for the offspring could be anywhere from 16 to 24 micron. Which is why you need to measure the performance of offspring even from fully performance recorded parents. In practice we don’t see enough offspring from a single set of parents to see the full range of possible outcomes.
If you breed an alpaca that turns out to be better than either of its parents then well done! Interestingly the odds of that happening are just the same as breeding an alpaca that is worse than both of its parents.
By using data from the registry and measures taken by breeders EBVs can be calculated. In practice breeders need to weigh the shorn fleece, whether skirted or not, and send off a mid-side sample for analysis as well as record shearing dates.
The table below summarises what is required and what the EBV calculated will be like.
|Date of Birth
|Micron Average Diam
|Yes – negative finer than average
|Standard Deviation mic diameter
|Yes – negative less variation than average
|Yes – negative less coarse fibres than average
|Spinning fineness – Mic
|Yes – negative finer than average
|Staple Length mm
|Yes – positive is longer than average
|Yes – positive more crimp than average
|fleece weight (kg)
|Yes (standardised to 365 days) positive heavier than average
|skirted (yes or no)
|previous shearing date
|Micron measures from the same alpaca in a series of years
|Persistence of fineness – probably expressed as micron per year, smaller good.
To make it easy to do there is an Excel template which the breeder can fill in and send to the BAS CEO by email.
The raw data will remain confidential to the owners. The aim is for EBVs derived from the raw data to be published to help members understand how EBVs work and make breeding decisions. Historic data is also valuable if you have it in your records because the calculation of persistence of fineness needs repeated measures.
In the autumn data from breeders will be collated and the EBVs will be calculated by SRUC.
The aim is that BAS members will use the data to:
If you are not already part of the project, then contact the BAS CEO for more information by emailing email@example.com.