Physical Evaluation of Bulls

128 Beef Breeder MANUAL Typically; • About 10 of bulls break down in the irst few weeks of mating • The average working life of a bull is around three years • After ive years of age the breakdown rate is about 35 per year. Clearly, structural soundness of bulls is a critical issue. As conformational traits are of medium inheritance, introducing a bull with a structural problem is likely to pass that problem on to his progeny. Bulls should be structurally sound in legs, feet, joints and all components of the reproductive tract.

5.3.2. Physical Evaluation of Bulls

Evaluating bulls intended for use in a breeding program is an essential part of the breeding process. To determine how well bulls are equipped to be successful breeding animals, an assessment of four major factors is required. Each of these factors inluences the fertility of an individual bull. The four main factors are: • Physical or structural soundness of the animal • Scrotal circumference and tone • Semen quality • Ability and desire to mate. For a bull to successfully pass an evaluation the bull must: • Pass a physical examination of the important structural components legs, feet, penis and sheath prepuce • Meet minimum requirements for scrotal circumference refer Section 5.3.5. and have a irm tone not soft or hard • Semen testing must show at least 30 of sperm are motile moving and sperm cell morphology must exceed 50 normal for natural mating in multiple sire groups, and exceed 70 normal for single sire mating or if intended for use in an artiicial insemination AI program • Show both the desire libido and ability to physically mount and mate with a cow. A bull must meet these minimum criteria in all categories to pass an evaluation. These criteria are relatively easy to test as outlined in 5.3.3 - Structural Soundness and Body Conformation. The main reasons why bulls are culled include: Arthritis - about 50 of bulls are culled because of loss of mobility due to arthritis. Arthritis is caused by poor leg and joint structure. Grain feeding of bulls as yearlings accelerates the onset of arthritis and joint problems. Injury - caused through ighting, accounts for about 10 of bull wastage. Broken penis - 15. This problem is usually found in bulls in their irst season, or in older bulls as arthritis begins to afect serving ability. Poor serving ability caused by structural problems particularly straight hind legs is the major cause of a broken penis. Corkscrew penis - 15. The penis corkscrews as the bull mounts, making service diicult if not impossible. This condition often only appears when a bull is 3-4 years of age, and gets worse as the bull gets older. Sheath problems - prepuce or sheath infections account for about 5 of bulls culled. Pendulous sheaths contribute to sheath problems. Overgrown feet - 5. Feet defects such as scissor claw and uneven toes are inherited feet problems - overgrown feet is generally a sign of poor leg structure. 129 Cold Winter Climates

5.3.3. Structural Soundness and Body Conformation