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Doktorsavhandling2023Öppen tillgång

Identification of bull semen microbiota and possible alternatives for antibiotics in semen extenders

Cojkic, Aleksandar


The use of 16S rRNA sequencing has revolutionised research on the microbiome. However, few studies using this method have been done on semen from healthy bulls. Such information is required to optimise addition of antibiotics to semen extenders to inhibit growth of bacteria. With the increasing emergence of antibacterial resistance, it is important to identify alternatives to antibiotics in semen preservation. Possible solutions are to use plant-based substances that exhibit antimicrobial properties or to separate spermatozoa from bacteria in semen samples. The aims of this thesis were to identify the seminal microbiome of healthy bulls, to assess individual differences and their influence on fertility as well as seasonal differences in the occurrence of bacteria and their possible impacts on sperm quality. A second aim was to explore alternatives to antibiotics to reduce bacteria, using plant extracts or by physical removal of bacteria from semen samples. The studies revealed individual differences in bull seminal microbiota that may be correlated with fertility. Seasonal differences were observed in the bacteria in commercial semen samples; however, no significant associations were found between specific bacteria and sperm quality. When evaluating alternatives to antibiotics, we noted that curcumin extract at a concentration of 5% reduced the bacterial count and had a slight positive effect on bull sperm kinematics without negatively affecting sperm viability. Single layer centrifugation (SLC) effectively removed bacteria from bull semen samples while simultaneously selecting good quality spermatozoa. More studies are needed to investigate the influence of certain bacteria on bull sperm quality. The effects of combinations of plant-based substances on bacterial reduction and sperm quality could be investigated, and also further possibilities with SLC. These methods could contribute to reducing the development of antimicrobial resistance.


16S sequencing; male fertility; season; sperm quality; bacteria; plant-based substances; Single Layer Centrifugation

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Acta Universitatis Agriculturae Sueciae
2023, nummer: 2023:51ISBN: 978-91-8046-154-2, eISBN: 978-91-8046-155-9
Utgivare: Swedish University of Agricultural Sciences

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