Читать книгу Bovine Reproduction - Группа авторов - Страница 124

Selection for conformation has been influenced by judges for show purposes and is not always the conformation most desirable for durability of the bull in a pasture or range environment. Because a bull is required to cover large areas and mount and lunge multiple times in a single day, feet and legs are often the trait that determines his ability to service cattle and his longevity as a sire. Hoof and hock abnormalities lead to lameness, which affects his ability to accomplish this purpose, as well as lowering sperm quality. Screw claw, chronic laminitis, and interdigital fibromas are common. The incidence of screw claw (Figure 8.1) appears to be increasing in beef breeds and is considered heritable by the American Association of Bovine Practitioners Lameness Committee [1]. Moving up the legs, stifle and hock injuries such as collateral ligament rupture, meniscal injuries, and anterior cruciate ligament (ACL) rupture should all be investigated as they will interfere with copulation and fertility [2]. Less common and sometimes more difficult to diagnose are shoulder injuries and spinal injuries or disease [2]. These abnormalities should be recorded in the feet and legs section of the BBSE form. Defects that may be inherited should be listed in the comment block with a statement that recommends use in a terminal cross only. Research has shown that animals with shorter hoof length and greater dorsal hoof angle develop less hoof lameness [3]. Dorsal hoof angles of 50 and 55° in the rear and front hooves, respectively, appear to be the more desirable. The angle of the hock should be between 155 and 170° – this being based on information derived from the Conformation Determination System (CDS), which was a method of relating hock angles of dairy heifers with other anatomical landmarks and then correlating those metrics with the incidence of future unsoundness [4].

Figure 8.1 A three‐year‐old Angus bull that exhibits the screw claw abnormality. This bull will require annual hoof trimming to remain sound.