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Genetic Selection Principles BY MATT SPANGLER, PH.D., PROFESSOR AND BEEF GENETICS EXTENSION SPECIALIST, UNIVERSITY OF NEBRASKA-LINCOLN

S ire selection does not need to be of data (information) available to make sire selection decisions and to clearly identify breeding goals. Basics of Expected Progeny Differences (EPDs) Too often seedstock producers and bull buyers get caught up in the actual weights, ultrasound data, etc., when selecting sires. EPDs provide a measure by which animals within a breed can be compared to one another for their genetic potential as par- ents for specific traits. EPDs incorporate multiple sources of information, including full pedigree, an animal’s own record and progeny information. As additional sources of information become available, the accu- racy of the EPD value increases. Why do “good” sires sometimes have “bad” calves? Why do full siblings some- times look and perform very differently? One potential reason is the phenomena of Mendelian sampling. Mendelian sampling arises because each parent passes a sample with half of its alleles to its offspring, and every allele has an equal likelihood of be- ing passed on. This effect can be quantified using contemporary group deviations and is a measure of how much better or worse an animal is compared to the average of his parents. One could envision a scenario in which an animal could receive only the most de- This effect can be quantified using contemporary group deviations and is a measure of how much better or worse an animal is compared to the average of his parents. overwhelming or complex. The key is to understand the various sources

sirable alleles from both parents, result- ing in a favorably large Mendelian sampling effect or the exact opposite, which could result in an unfavorably

2018 CONVENTION

large sampling effect. Perhaps the best ex- ample is a set of flush mates. Although all of them have the same pedigree estimate EPD, they differ considerably in terms of performance. Consequently, their EPDs, once they have a record, differ due to Men- delian sampling. Relatively recent advances in the use of genomic tools allow more accurate estimates of the relationships be- tween animals, thus capturing part of the Mendelian sampling variation. This is why the inclusion of genomic information into EPDs increases EPD accuracy, particularly for young animals. EPDs Compared to Raw Data and Ratios Many producers mistakenly place more emphasis on raw measurements than EPDs. Raw measurements include the confounded effects of genetics and environment, mak- ing it difficult to know an animal’s true ge- netic ability. Below is a very simplistic equa- tion describing an animal’s phenotype. P = G + E Where P is the phenotype, G is the genet- ic effect and E is the environmental effect. The phenotype is what is seen or mea- sured, such as actual weights or carcass measurement. Both genetics and the envi- ronment influence these values, and be- cause we are interested in identifying ani- mals based on their potential as parents, the environment should not be included in the tool used to select animals. Further- more, actual phenotypes (e.g., weights, 

Akaushi Prime Time • Winter 2019

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