Читать книгу Bovine Reproduction - Группа авторов - Страница 106

In Canada, there have been two systems utilized for BBSE [16]. Some practitioners follow the American SFT guidelines described previously, while the Western Canadian Association of Bovine Practitioners (WCABP) has produced its own guidelines and forms. The WCABP BBSE process is similar to the SFT guidelines except for varied thresholds for SC, morphologically normal sperm, and sperm motility

[16].

In contrast to the SFT system, the WCABP system considers breed and age when setting the SC threshold. In the SFT system, the lower SC threshold is the same (30 cm) for bulls of any Bos taurus breed between 12 and 15 months of age [10]. However, in the 2018 version of the SFT BBSE manual there is recognition of the profound influence of breed and age on SC, providing veterinarians with information to tailor recommendations to clients with different breeds. The WCABP system sets the SC threshold for each breed and age as one standard deviation below the mean [17], which means that 16% of bulls with the smallest SC may be culled. Both systems classify bulls as having either satisfactory or unsatisfactory SC scores, but do not further categorize satisfactory bulls to allow positive selection pressure based on SC.

For sperm motility and sperm morphology, the SFT system categorizes bulls as either satisfactory or unsatisfactory, while the WCABP system adds another category called questionable for bulls whose values are slightly below the set threshold. As a result, in the WCABP system there are four possible overall classifications for bulls, ranging from satisfactory, questionable, decision deferred, or unsatisfactory breeders. The decision deferred classification is used for bulls that are expected to show a substantial improvement in semen quality before the breeding season, thereby warranting a re‐evaluation within several weeks [18].