Copy of `University of Missouri - Cattle glossary`

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University of Missouri - Cattle glossary Category: Agriculture and Industry > Cattle Date & country: 11/09/2007, USA Words: 114

Reference sire
A bull designated to be used as a benchmark in progeny testing other bulls (young sires). Progeny by reference sires in several herds enable comparisons to be made between bulls not producing progeny in the same herd(s).

Regression (regressed)
A measure of the relationship between two variables. The value of one trait can be predicted by knowing the value of the other variable. For example, easily obtained carcass traits (hot carcass weight, fat thickness, ribeye area and percent of internal fat) are used to predict percent cutability. Likewise, breeding value estimates based on limited data are regressed back toward the population average to account for the imperfection of this relationship.

Rotational crossbreeding
Systems of crossing two or more breeds where the crossbred females are bred to bulls of the breed contributing the least genes to that female's genotype. Rotation systems maintain relatively high levels of heterosis and produce replacement heifers from within the system. Opportunity to select replacement heifers is greater in rotation systems than in other crossbreeding systems.

Scrotal circumference
A measure of testes size obtained by measuring the distance around the testicles in the scrotum with a circular tape. Related to semen-producing capacity and age at puberty of female sibs and progeny.

Scurs
Horny tissue of rudimentary horns that are attached to the skin rather than the bony parts of the head.

Seedstock breeders
Producers of breeding stock for purebred and commercial breeders. Progressive seedstock breeders have comprehensive programs designed to produce an optimum, or desirable, combination of economical traits (genetic package) that will ultimately increase the profitability of commercial beef production.

Selection
Causing or allowing certain individuals in a population to produce offspring in the next generation.

Selection differential (reach)
The difference between the average for a trait in selected cattle and the average of the group from which they came. The expected response from selection for a trait is equal to selection differential times the heritability of the trait.

Selection index
A formula that combines performance records from several traits or different measurements of the same trait into a single value for each animal. Selection indexes weigh the traits for their relative net economic importance and their heritabilities plus the genetic associations among the traits.

Sibs
Brothers and sisters of an individual.

Sire summary
Published results of national sire evaluation programs.

Systems approach
An approach to evaluating alternative individuals, breeding programs and selection schemes that involves assessment of these alternatives in terms of their net impact on all inputs and output in the production system. This approach specifically recognizes that intermediate optimum levels of performance in several traits may be more economically advantageous than maximum performance for any single trait.

Terminal sire
Sires used in a crossbreeding system where all their progeny, both male and female, are marketed. For example, F1 crossbred dams could be bred to sires of a third breed and all calves marketed. Although this system allows maximum heterosis and complementary breeds, replacement females must come from other herds.

Trait ratio
An expression of an animal's performance for a particular trait relative to the herd or contemporary group average. It is usually calculated for most traits as: