Sperm morphology in progeny-tested Swedish AI dairy bull sires

Abstract: Use of bull semen with high levels of sperm abnormalities, reflecting genital dysfunction, is not recommendable to use for AI since it most likely leads to subfertility. If sperm morphology deteriorates with age, it becomes a source of concern when using ageing progeny-tested AI-bull sires. However, whether a relationship between sperm morphology and fertility after AI in progeny-tested bull sires is present remains to be proven and constituted the reason for a retrospective study of progeny-tested bull sires of the Swedish Red and White (SRB) and Swedish Holstein (SLB) breeds performed with data of 8 SRB and 4 SLB sires analysed in an University specialized andrological laboratory. Particular attention was paid to the influence of age and breed as well as the variation between- and within-bull for presence and level of sperm abnormalities. Sperm morphology differed between sires, ejaculates and breed, with 6/12 sires having ejaculates with more than 10% of morphologically deviating sperm heads, an used threshold for young AI bulls. However, with the exception of pear-shaped or narrow at the base anomalies, individual defect mean values were always within what is expected for a bull sire, and considered within acceptable limits. Breed and bull within breed age affected some semen (ejaculate volume) and most sperm morphology variables, while age significantly affected only few sperm morphology variables (nuclear pouches and sperm head contour). Estimated breeding values for male fertility output differed significantly among bulls and, when all ejaculates were accounted for, the percentage of morphologically normal spermatozoa was positively related to fertility. Few individual sperm abnormalities in all ejaculates correlated significantly to fertility, as pear-shaped sperm heads. When separated by breed, these correlations were restricted, in SRB bulls, to the normal spermatozoa in wet smears, or lost in SLB bulls, probably owing to the reduced sire material examined. In conclusion, the presence of some relationships between sperm morphology and fertility after AI calls for routine, frequently done assessments of sperm morphology in AI-stud bull sires during their entire active life.