Terminology
What is the definition of genotype?
The genetic composition of an individual.
Which trait type usually has the highest heritability: reproduction, growth, or carcass?
Carcass traits usually have the highest heritability.
What does EPD stand for?
Expected Progeny Difference.
If Sire A has BW EPD +5 and Sire B has –2, how much heavier will A’s calves be on average?
Sire A’s calves = 7 lb heavier on average.
Define an economically relevant trait (ERT).
Traits that directly affect profitability in a commercial herd.
Which bulls are better for heifers: Maternal or Terminal?
Maternal bulls (calving ease, lower BW) are better for heifers.
What is the difference between homozygous and heterozygous alleles?
Homozygous = same allele pair (BB, bb); Heterozygous = different alleles (Bb).
What is heritability?
Heritability = proportion of observed differences that can be passed to progeny (0–1 scale).
EPDs are expressed in what units?
Expressed in trait units (e.g., pounds, centimeters).
What does accuracy (ACC) represent?
Accuracy = amount of information used to calculate an EPD; reliability.
Which EPD is an indicator of calving ease?
Birth Weight, Calving Ease Direct, Gestation Length.
Which type of bulls focus on growth and carcass?
Terminal bulls focus on growth and carcass.
Which type of traits are controlled by one or two genes: qualitative or quantitative?
Qualitative traits are controlled by one or two genes.
Define generation interval.
Generation interval = average age of parents when their replacements are born (≈ 5–6 years in cattle).
EPDs are breed-specific – True or False?
True
What accuracy level is considered “good” (>0.80, 0.60–0.80, or <0.40)?
>0.80 is considered “good accuracy.”
Give an example of a carcass trait EPD.
Carcass weight, ribeye area, marbling, fat thickness.
Why is multi-trait selection important?
Multi-trait selection avoids antagonisms between traits.
Give an example of a qualitative trait in cattle.
Example: coat color, horned vs. polled, dwarfism.
Which selection method is the most effective: Tandem, Independent Culling, or Selection Index?
Selection Index = most effective.
Name one factor that EPDs account for (e.g., management/environment differences).
Different management and environment, genetic trend, merit of mates, culling for performance.
Which is more reliable: raw weights, ratios, or EPDs?
EPDs are most reliable.
Name two traits included in economic indexes (like $B, API).
Weaning weight, yearling weight, marbling, feed intake, cow energy value.
Name one visual trait you must still evaluate in bulls (besides EPDs).
Structural soundness, reproductive soundness, temperament, body capacity.
Explain the difference between genotype and phenotype.
Genotype = genetic code; Phenotype = observable expression (genotype + environment).
Why does selecting for more traits slow down progress?
Because selection pressure is divided → progress per trait is slower.
How often are sire summaries usually published?
Usually 1–2 times per year.
Why should yearling bulls be used with caution in sire selection?
Yearling bulls = low accuracy, based only on own performance + pedigree.
Why are economic indexes useful for commercial producers?
They simplify selection by combining multiple traits into a single economic value.
Why should high-growth sires be avoided in low-feed environments?
Because they increase maintenance cost and may not adapt to limited feed.