The Advantage of Genetic Evaluations

The growth of an animal at weaning is influenced by environmental factors as well as genetic factors.  Environmental factors include such things as management, nutrition, weather conditions, season of calving, and so on.  Genetic evaluations are superior to all the other methods of selection for a trait because it adjusts for the environmental differences, takes into account the animals pedigree and is a prediction of true genetic merit. 

The Basics on Genetic Evaluations

The calculation of Genetic Evaluations and Across Breed EPDs (ABCs) is quite simple in its basic conceptual form. Generally, genetic evaluations are modeled based on three key aspects;

·        Animal Relationships (Pedigree)

·        Multiple Trait Evaluation

·        Environment

Animal Relationships

All animals receive 1/2 of their genes from the dam and 1/2 of their genes from the sire. Therefore, every animal will have a relationship to other animals which provides some very important connections that are used to calculate genetic evaluations, not only within the herd but also across herds which may have related animals

Multiple Trait Evaluation

Multiple trait evaluation is a calculation method that uses information about how different traits that are related. The relatedness is accounted for by genetic a correlation, which indicates how much two things vary together. For example, weaning gain is related to yearling gain. This has the effect of adding more information to each of the trait’s evaluations, therefore improving the accuracy.

Environment and Management Groups

Environment is defined as the things that make one farm different from another. The concept of management grouping (sometimes called contemporary groups) is what allows the genetic evaluation procedure to separate environmental influences from genetic influences.  It is very important that animals in a management group are treated alike and had equal opportunity to perform.  We do not need to know absolutely everything about how the animals were fed, but we instead look at the differences from the average animal in that group for the estimation of genetic merit.  Animals are grouped by herd, year, age and management programs.  This grouping accounts for differences between:

·        herd owners and their cattle management practices;

·        years, and the effect of wet or dry summers on pasture conditions etc.;

·        age groups; and

·        how cattle have been fed or handled.

BIO has developed requirements for the definition of  a management group that allows for the calculation of genetic evaluations.

Management Group Requirements

The Computation of Genetic Evaluations

Genetic evaluations are computed using sophisticated computer programs that are designed to express all the available information in the form of a genetic prediction.  If one could write the formula for the computation in words it would be:

Genetic evaluation = Actual measurement

                                    + adjustment for breed, age, sex

                                    + adjustment for management group (environment)

                                    + adjustment for information from related traits

                                    + adjustment for genetics of related animals

Adjustment for genetics of related animals is one of the key components that allows genetic comparison across herds and years.  Information from parents, progeny, grandparents, half-sibs, full-sibs, cousins and all other relatives' performance are used in the calculation.

Accuracy of Genetic Evaluations

Every genetic evaluation has an associated accuracy value.  Accuracies ranges from 1 to 100 and relate to the reliability of the estimate.  Genetic evaluations with high accuracies are based on more performance information and are more reliable.

Some traits are controlled by genetics more than others.  Accuracies are generally higher for traits that are controlled more by genetics, because more genetic information is known from each weight or measurement.  Growth traits and carcass traits or more genetically controlled than reproductive traits and have higher accuracy values.

For some animals, performance information is not available or it was not raised in a management group that met the minimum requirements.  As a result, the genetic evaluation for this animal is based solely on pedigree information and data from related traits.  The accuracy of this evaluation is quite low due to the limited amount of information.  To indicate this lower reliability, the accuracy for evaluations without a performance record is labeled ‘PE’, which stands for pedigree estimate.

Scale of Genetic Evaluations

Genetic evaluations are reported in units of the trait.  They are expressed as a difference between an animals genetic ability and a base population. 

 Beef Improvement Ontario’s genetic evaluations have a base defined as the average animal born between 1995 and 1998.  The base number for each trait is shown in the following chart.

 Because genetic evaluations are expressed relative to a base population, it is difficult to understand how an animal ranks compared to other animals of the same breed or population.  For this reason, percentile ranks were developed.

Percentile Ranks

Percentile ranks were developed to provide a measure of how good a genetic evaluation is compared to the current population of animals.  For each genetic evaluation, there are two percentiles ranks – one indicating the rank compared to all other breeds, and a second indicating its rank compared to animals of the same breed.  The percentile ranks range from 1 to 99 – higher numbers are better. 

For more information on Beef Improvement Ontario's Genetic Evaluations, or to find out how you can receive Genetic Evaluations on your animals, please call the BIO office at 1-800-373-2253.