Selection Practices from Guidelines for Uniform Beef Improvement Programs by the Beef Improvement Federation (BIF)
Sire selection. To make sustained contributions to the breeding program, bulls should be structurally and reproductively sound. Approximately 20% of all beef bulls have some degree of infertility. A thorough breeding soundness examination, performed by an experienced veterinarian or other competent personnel, can detect the majority of bulls having obvious fertility problems and should be performed annually on all bulls two to four weeks before the start of mating. As described in Appendix 6.1, components of the breeding soundness examination include a physical examination, measurement of scrotal circumference, rectal palpation of internal organs, and examination of semen for progressive linear motility and normal morphology.
Sound feet and legs are essential in order for a bull to cover many acres of pasture, both for obtaining adequate nutrition and mating cows. Structural soundness is not an all-or-none phenomenon; rather it is expressed in various degrees. Bad feet, pigeon toes, excessively straight or sickle hocks, and loose or pendulous sheaths are examples of some of the more common structural problems of bulls. Because many structural problems become worse as bulls grow older and heavier, it is particularly important to critically evaluate young bulls.
Structural soundness of bulls that are candidates for selection should be evaluated in a systematic manner. Inspect each bull‘s feet, toes, heels, pasterns, knees, hocks, and sheath. When viewed from the front, the feet should point straight ahead, both when the bull is standing and walking. The feet should be large and round with a deep heel and with toes that are similarly sized. When viewed from the rear, the legs should be equally far apart at the hocks and pasterns and then toe out slightly from the pasterns to the ground. The bull should move freely with each hoof striking the ground evenly.
Many structural problems are partially heritable and should be particularly discriminated against when daughters will be kept for replacements. However, structural problems that do not compromise longevity or ability to service cows are of little consequence in the selection of terminal sires.
Evaluating bulls for structural soundness also provides an opportunity to gauge a bull‘s temperament or disposition, a moderately heritable trait. A bull with poor disposition may be dangerous or difficult to work, and his daughters may be difficult to manage as well.
For traits for which they are available, EPDs most efficiently combine phenotypic performance data, records from all related animals, and information from genetically correlated traits to predict the relative performance of future progeny of candidates for selection. Information from these sources is optimally combined into a single predictor of genetic merit. Therefore, there is no advantage in using information from sources that contribute to the EPD when the EPD itself is available. For example, if the EPDs forbirth weight are available on two candidates for selection, then these statistics provide a more accurate indication of the difference in birth weights of future progeny than the actual or adjusted birth weight records of the candidates themselves. Likewise, if the selection criterion is calving ease and calving ease EPDs are available, then consideration of birth weight EPDs is unwarranted.
Ratios of animal records to their contemporary group average describe the magnitude of an individual‘s phenotype relative to other animals managed in a similar fashion. In calculating contemporary group ratios, no information is used from related animals in other contemporary groups or from genetically correlated traits. Contemporary group ratios are most useful when EPDs are not available for an economically important trait.
Appropriate use of performance records and EPDs allows producers to increase genetic potential for profit. Profit is determined both from income (a function of reproductive rate, growth rate, and product quality) and expense ( a function of feed requirements and managerial interventions). Thus, to improve genetic potential for profit, selection decisions must consider several traits simultaneously. Because genetic antagonisms exist among some of the traits influencing profit, selection for extreme phenotypes or genotypes frequently is not warranted. It is far more likely that the greatest profit will be realized from cattle with an optimal balance among traits.