Beef Cattle Terminology continued

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 for rotation systems than for 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 occurs when individuals of different genetic or phenotypic merit reproduce at different rates.
Relevant types of selection include:

•  Artificial selection. The livestock breeder decides which individuals will reproduce and for how long. Ideally, animals with highest predicted genetic merit for economically important traits are chosen as parents, and those with the poorest estimated genetic merit are rejected or culled.
•  Natural selection. Whether an animal reproduces, and for how long, is determined by that animal’s ability to cope with environmental challenges, rather than or in addition to breeder decisions.
•  Directional selection. Animals chosen to be parents are above (or below) the average of their contemporaries for the trait in question. The goal of directional selection is to improve phenotypic merit of the selected traits in progeny of the selected individuals.
• Stabilizing selection. Those animals closest to average of their contemporaries are selected as parents, while animals that are either well above or well below average are discriminated against. The goal is to maintain the trait in question at its current level of expression. Stabilizing selection is appropriate for traits for which the optimum phenotype is an intermediate value.

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.

Selection Intensity -- Selection intensity is a numerical measure of a breeder’s attempt to change a trait by choosing as parents those individuals with better than average estimated transmissible genetic merit for that trait. If all other things are equal, then higher selection intensity leads to higher selection response.

Selection Response -- Selection response is the amount by which the population mean for a trait is changed by the effects of selection, generally expressed per unit of time. See also correlated selection response.

Sibs--Brothers and sisters of an individual.

Sire summary--Published results of national sire evaluation programs.

Stressor -- A stressor is any external challenge that causes an animal to initiate a physiological, behavioral and(or) immunological response to maintain or achieve its physical integrity and well-being. Examples include environmental temperatures outside the animal’s inherent comfort zone, pathogenic organisms and dietary toxins.

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 sires--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 of 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:

     Individual record

----------------------------  x 100

Average of animals in group

The exception to this is birth weight ratio. It is calculated as:

            Adjusted birth wt. of individual

200 -  -------------------------------------------------

      Average adjusted birth wt. of contemporary group

USDA Yield Grade--Measurements of carcass cutability categorized into numerical categories with 1 being the leanest and 5 being the fattest. Yield grade and outability are based on the same four carcass traits.

Variance--Variance is a statistic that describes the variation we see in a trait. Without variation, no genetic progress is possible, since genetically superior animals would not be distinguishable from genetically inferior ones.

Weight per day of age (WDA)--Weight of an individual divided by days of age.