Animal Breeding Genetics: BLUP, EPDs, and Sire Selection

What is large-scale genetic evaluation?

Genetic evaluation of large populations, such as entire breeds, to compare animals and improve selection.

What is the purpose of large-scale genetic evaluation?

To compare genetic merit among animals from different herds or flocks.

What is selection intensity?

How selective breeders are when choosing animals to reproduce.

What happens when selection intensity increases?

The potential rate of genetic improvement increases.

What are central tests?

Tests that compare animals from different herds or flocks under a common testing environment.

What were the limitations of central tests?

They evaluated few traits, focused on individual performance, and could be affected by testing location.

What is BLUP?

Best Linear Unbiased Prediction.

What is the purpose of BLUP?

To predict genetic merit while accounting for fixed environmental effects and genetic relationships.

When did BLUP become widely used?

The 1980s.

What is BLUE?

Best Linear Unbiased Estimation.

What does BLUE estimate?

Fixed effects, such as sex and management groups.

What does BLUP predict?

Random effects, including animal breeding values.

What is a fixed effect?

A systematic effect included in a model, such as sex or management group.

What is an EBV?

Estimated Breeding Value; an estimate of an animal's additive genetic merit for a trait.

What is an EPD?

Expected Progeny Difference; the expected difference in average offspring performance due to a parent's transmitted genetics.

What is MPPA?

Most Probable Producing Ability; a prediction of an animal's future producing ability based on repeated performance.

What is a direct genetic effect?

The effect of an individual's own genes on its performance.

What is a maternal genetic effect?

The effect of the dam's genes on the environment she provides for her offspring.

What is the direct component of weaning weight?

The calf's own genetic ability to grow.

What is the maternal component of weaning weight?

The dam's genetically influenced milk production and mothering ability.

What is a direct EPD?

An EPD that predicts differences in offspring performance due to their own inherited growth or performance genes.

What is a maternal Milk EPD?

An EPD that predicts the maternal influence of a sire's daughters on their calves' weaning weights.

What is Total Maternal EPD?

A prediction combining a sire's daughters' maternal ability and the growth genetics they transmit to their calves.

What is the formula for EPD?

EPD = EBV / 2.

What is the formula for EBV using EPD?

EBV = 2 × EPD.

What is the formula for the difference between two EPDs?

EPD difference = EPD A − EPD B.

What is the formula for Total Maternal EPD?

Total Maternal EPD = Milk EPD + (Weaning Weight EPD / 2).

What is a sire summary?

A list of genetic predictions, accuracy values, and other information about sires in a breed.

What information is included in sire summaries?

EPDs, accuracy values, and other genetic information about sires.

What is the purpose of a sire summary?

To help breeders compare sires and make genetic selection decisions.

Why are sire summaries emphasized instead of dam summaries?

Sires can produce many more offspring and influence genetic change across more herds.

What is artificial insemination (AI)?

Breeding an animal using collected semen without natural mating.

How does AI help genetic improvement?

It allows genetically superior sires to produce offspring across many herds.

What does a weaning weight EPD predict?

Expected differences in the average weaning weights of a sire's progeny.

What does a Milk EPD predict?

The maternal contribution of a sire's daughters to their calves' weaning weights.

What does an EPD of zero mean?

It represents the zero point of the genetic base used in the evaluation.

What is a genetic base?

The reference level against which breeding values or EPDs are expressed.

What is a base year?

A reference year used to establish the genetic base of an evaluation.

Can EPDs from different breeds be directly compared?

Generally no, because breeds may have different genetic bases.

What does EPD accuracy indicate?

How reliable or uncertain an EPD prediction is.

What does high EPD accuracy mean?

Less uncertainty and lower selection risk.

What does low EPD accuracy mean?

More uncertainty and higher selection risk.

What is selection risk?

The uncertainty that an animal's true genetic merit differs from its predicted genetic merit.

What is the formula relating accuracy to reliability?

Accuracy = square root of reliability.

What is the formula for reliability?

Reliability = Accuracy squared.

What can improve the accuracy of genetic predictions?

More informative performance, pedigree, progeny, or genomic data.

What is a contemporary group?

A group of animals raised under similar environmental and management conditions.

Why are contemporary groups important?

They allow fairer genetic comparisons by accounting for shared environmental conditions.

What is connectedness?

The genetic relationships linking animals in different herds or contemporary groups.

Why is connectedness important?

It improves the ability to compare genetic merit across herds.

How does AI increase connectedness?

The same sire can produce offspring in multiple herds.

What is genotype by environment interaction (G × E)?

When the effects of genotype on performance differ depending on the environment.

What is a low-heritability trait?

A trait for which additive genetic differences explain a relatively small proportion of phenotypic variation.

What is a pedigree error?

Incorrect information about an animal's ancestry.

What is parental misidentification?

Incorrectly identifying an animal's sire or dam.

What are performance records?

Recorded measurements of an animal's traits or production.

What is falsification of performance records?

Deliberately reporting incorrect performance information.

What is incomplete reporting?

Failing to submit all relevant performance records.

What is the most common performance-record problem according to the notes?

Incomplete reporting.

What are environmental adjustments?

Statistical corrections for known nongenetic influences on performance.

What is a contemporary-group error?

Assigning animals to the wrong comparison group or ignoring management differences.

What is poor connectedness?

Insufficient genetic relationships between groups to support precise comparisons.

What are the major problems with genetic evaluation?

Incorrect pedigrees, faulty performance records, incorrect adjustments, contemporary-group errors, weak connectedness, and G × E interactions.

What is the relationship between EPD and progeny performance?

EPDs predict expected differences in progeny averages, not exact individual performance.

What two phrases are important when interpreting EPDs?

On average and progeny.

What is genetic change?

A change in the average genetic merit of a population over generations.

What is the purpose of breed associations in genetic evaluation?

To collect data and coordinate breed-wide genetic evaluations.

What is the main advantage of BLUP over simple performance comparisons?

It uses genetic relationships and adjusts for systematic effects to improve genetic predictions.