Bull/Semen Selection

Sire selection involves either using a natural service bull, semen through AI or both. A big difference between using natural service verses semen is the visual appraisal of the bull. With natural service you have the benefit of evaluating the bull in person, but typically on unproven bulls the EPD have lower accuracy. With semen visual appraisal is typically through a photo, video or personal communication with a sales representative, however, AI sires often have higher accuracy EPD.

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 Breeding Soundness Exam, 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.

In natural service bulls 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 hooves 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.

Since many structural problems are heritable it is important to evaluate the structure of both natural service and AI sires. Structure has increased importance 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.

When selecting a natural service bull temperament is another phenotypic trait to consider. A bull with poor disposition may be dangerous or difficult to work, and his daughters may be difficult to manage as well. Many breeds compute Docility EPDs and these can be used to select for improved temperament in the offspring, but it is also important to assess the phenotypic temperament of natural service bulls for safety and management purposes.

For traits that they are available, EPD are the best tool available for making selection decisions. There is no advantage in using information from sources that contribute to the EPD when the EPD itself is available. For example, when selecting for calving ease in a sire the best tool available is the Calving Ease Direct EPD; there is no advantage to also look at the bull's calving ease score, actual birth weight or even his Birth Weight EPD because all of this information is included in the Calving Ease Direct EPD.

Single-trait selection is rarely recommended and traits used in selection should be based on the breeding objectives . Selection for more than one trait at a time is optimally implemented using selection index methods. When EPDs are available for all economically relevant traits, calculating the sum of the products of EPD weighted by their economic values provides a single straightforward criterion for evaluating candidates for selection.