Estimated Breeding Values (EBVs) estimate the genetic worth of animals. They are produced for each animal for each recorded trait from Lambplan using BLUP technology. EBVs use the same units as the recorded traits (ex: kg for liveweight, mm for fat and loin depth, and % for number lambs born or reared) and are expressed relative to a common baseline for all animals in all contemporary groups. In the Tamarack flock that baseline was established in the mid 90's.

Because BLUP takes environmental influences into account and all EBVs are expressed relative to a common base, direct comparisons can be made across flocks (as long as they are linked genetically). Across-flock BLUP increases the size of the genetic pool from which replacements can be accurately chosen, thus increasing selection intensity and reducing the risk of inbreeding.

Comparisons can also be made between animals across time allowing measurement of genetic progress. Genetic progress in a breed can be charted year by year, both nationally and on an individual flock basis.

In short an EBV is simply a description of that animal's performance in a trait as compared to the base for that flock or breed. The value of an EBV in one individual is compared to all the animals in its linked gene pool that is within that flock, and across flocks, as well as across years greatly increasing the accuracy of that information in predicting genetic superiority. (The more records the individual is compared to (with valid genetic links) the higher the accuracy of the information). So while an adjusted weight on an animal, his siblings, and his parents has an accuracy of 5-10%, the accuracy of an EBV on that same individual can be as high as 99% depending upon how much data is behind the number. As of 2006, the Tamarack flock has over 3436 records behind its EBVs with accuracies in the 70-90% range. This number will be increasing at a more rapid rate as links to other flocks are established.

Most of the sheep producing world has embraced the use of EBV's in their sheep selection programs, and the US has been a world leader in pork and dairy selection through the use of EBVs, yet U.S. sheep producers have been very slow to adopt the use of this proven selection technology due to a heavy emphasis on evaluating visual traits in the show ring. The result has been very little genetic progress in the US sheep population in the economically important traits.

Below is a more precise definition of each trait used in the Tamarack selection index:

MWWT = maternal weaning weight. MWWT EBV's are an estimate of the ewe's potential for milk production and ability to provide a better maternal environment. They are expressed as kilograms of weight at weaning. 80% of the mwwt is due to milk production so this trait is a good measure of milk producing ability. Expressed as kg of lamb weight.

NLB = number of lambs born. Estimates the genetic difference between animals for number of lambs born each lambing opportunity. Expressed as a %.

NLW = estimates the genetic difference between animals for number of lambs weaned each lambing opportunity. Expressed as a %. NLW has had a profound influence on improving lamb survival rate in the Tamarack flock.

WWT = weaning weight. Estimates the genetic difference between animals in liveweight at 60 days of age. Expressed as kg's of weight.

PWWT = post weaning weight. Estimates the genetic difference between animals in liveweight at 150 days of age. Expressed as kg's of weight.

PEMD = post weaning eye muscle depth. Estimates the genetic difference between animals in loin eye muscle depth at the ‘C' site (12 th /13 th rib). Expressed as mm of loin eye depth at 45 kg liveweight.

PFAT = post weaning fat depth. Estimates the genetic difference between animals in fat depth at the GR site. Expressed as mm fat depth at 45 kg liveweight.

Loin eye depth is used throughout the rest of the world as a measure of muscling. The US uses loin eye area. Research has found that ultrasound measurement of loin eye depth is more accurate than measuring area, and the correlation between depth and area is over 90%.

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For more information or questions, please contact:

janet@tamaracksheep.com

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