Effects of Age, Breed and Scrotal Circumference Interactions on Sperm Morphology of Bulls Raised on Commercial Farms in Zambia

The primary objective of this study was to investigate the effect of interaction of age, breed and scrotal circumference (SC) on the sperm morphological characteristics of bulls raised on commercial farms in Zambia. A total of 365 bulls comprising of 164 Boran, 139 Bonsmara, 35 Tuli, 12 Santagetrudis, 5 Holstein Friesian (HF) and 10 Sussex bulls were studied. Semen was collected once using an electro-ejaculator after which eosin-nigrosin stained semen smears were made. Thereafter, the eosinnigrosin stained semen smears were examined under a microscope for abnormal spermatozoa. The interaction between age categories and the Boran bulls did not differ from the interaction of Sussex bulls older than 72 months (mo) of age in predicting sperm abnormalities (P>0.05). However, Bonsmara and Sussex bulls older than 72 mo of age had lower percentages of sperm abnormalities (P<0.05). Interaction of age and Tuli bulls showed high midpiece and tail defects (dag defects and simple coiled tails), total abnormal sperm, major defects and the Proximal cytoplasmic droplets (PCD), (P<0.05). Santagetrudis bulls between 48 and 60 mo of age showed an increase in the midpiece defects, total abnormal sperm, major defects and the PCD, (P<0.05), but lower than those of the interaction between age and the Tuli bulls. Higher coiled tails were found due to the interaction between age and HF bulls compared to age and the Tuli bulls (P<0.05). The interaction between age and SC had an effect on sperm abnormalities, (P<0.05). The study suggested that the interactions of age, breed and SC are important sources of variation in sperm morphology. However, further research is needed to determine the effect of minor nutritional differences on the sperm morphological characteristics on the farms.