Using and Understanding Sheep EPDs When Purchasing Sheep

By Sarah Young Livestock Editor
Thursday, October 23, 2008 7:37 AM CDT

Expected Progeny Differences, EPDs, when understood and used correctly can aid sheep producers in purchasing decisions along with advancement and enhancement of their flocks.

Although the sheep industry may lag behind the cattle industry in EPD use, the information is becoming more readily available and producers need to take advantage based on their flock’s needs.

“The main purpose of your flock should drive your purchasing decision,” said Dr. Dave Thomas, UW-Extension sheep specialist during an educational seminar in conjunction with the first Badger Production Sale featuring UW-Madison sheep program genetics.

Visual traits

Visual traits, characteristics you can see, are highly heritable. These traits include general conformation of sheep, length, height and wool quality.

“Its (visual traits) are 50 to 60 percent heritable in livestock,” he explained.

Thomas encouraged producers to select for visual traits if they are important to the producer and meets the flock goals. Overall, if sheep look good their progeny tend to look good, too.

Production traits

Unlike the highly heritable visual traits, production traits cannot be “seen” and they have a lower heritability rate.

“The production traits themselves are lowly heritable,” said Thomas.

These production traits include, but are not limited to, loin eye area, lambs born, fat thickness, disease performance and weaning weights.

Thomas pointed out conformation traits have low correlations with most production traits, so solely basing purchasing decision on visual traits may not get producers the results they want and need.

Performance data can improve accuracy for production rates.

* Type of birth, rearing and litter size are available. “It’s a good place to start,” said Thomas. This EPD lets producers know if the lamb was born a single, twin or triplet. If an individual’s EPD is 21 it was born a twin and reared as a single. If it is 22 it was born a twin and reared a twin. A 12 would be born a single and reared as a twin. The first number relates to the number born and the second number is how it was reared, as a single or twin etc.

* Weaning and post weaning weights. These weights are “adjusted” to represent the type of birth and age of the dam. The EPD represents the lamb as if it had been reared a single by a mature dam between 3 and 6 years old. This EPD allows producers to compare “apples to apples” said Thomas. If the 60 day weaning weight is +2 and the 120 day weaning weight is +4.2 this means lambs of this ram are expected to weigh two pounds more at weaning and 4.2 pounds more at 120 days than a ram with a 60 day weaning weight EPD of 0.0 and 120 weaning weight of 0. Negative numbers in this category mean the weaning weights would be lower than and average (weaning weight EPD of 0.0).

* Carcass merit measures offer loin eye area, fat thickness, which are adjusted for body weight.

EPDs for production traits

These EPDs use powerful statistical genetic techniques. The EPDs are determined by combining production data of individuals and their relatives into the most accurate estimate of genetic value possible.

“The sheep industry is really just getting started with this,” explained Thomas.

The most beneficial part of EPDs is that the information is compatible within the flock and across other flocks enrolled in the National Sheep Improvement Program (NSIP) in the country. Additional EPDs available include:

* Maternal milk n genes for maternal influence. This EPD represents the daughter’s expected maternal influence and not the individual’s.

* Milk and Growth n represents the weight of the weaned lambs from the daughter. It is calculated by taking the maternal milk EPD plus half of the 60 day weaning weight. If the milk growth EPD is +1.0 it means daughters of the individual sheep are expected to wean lambs that are one pound heavier than lambs of daughters with a 0.0 EPD. If it is a -1.0, daughters are expected to wean lambs that are one pound lighter.

Scrapie genotype

Specific genotypes that provide genetic resistance to the most common form of scrapie found in North America. Genotypes are RR, QR and QQ.

“These genotypes do not mean anything about infections of scrapie,” he explained.

It allows for the selection of resistance depending on the sheep genotype. A genotype of RR is resistant, QR is very resistant and QQ is susceptible to scrapie.

Although RR is the best, sheep with the genotype of QR are almost 100 percent resistant. Almost all (99 percent) of scrapie infected sheep carry the genotype of QQ.

Thomas said producers should select sheep that “have at least one R allele.”

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