Stiftung Tierärztliche Hochschule Hannover (TiHo)TiHo eLib

Hypothermic, antibiotic-free preservation of boar semen is effective against multidrug-resistant Serratia marcescens

In boar semen, commonly preserved at 17°C, contamination with Serratia (S.) marcescens is a major problem due to its multidrug resist-ance and spermicidal effects. Our study tested the hypothesis that hypothermic semen preservation at 5°C inhibits the growth of S. marcescens. Ten semen samples from seven boars were diluted in an antibiotic-free AndroStar® Premium extender (Minitüb, Germany) to 20 × 106 sperm/ml. Three subsamples were prepared: S1: con-tamination with S. marcescens (5 × 102 CFU/mL), storage at 17°C (positive control), S2: contamination with S. marcescens, storage at 5°C and S3: storage at 5°C (negative control). In S1, the number of bacteria increased exponentially, reaching more than 1012 CFU/mL after 144 h. This coincided with an increase of agglutinated sperm, loss of motility evaluated by computer-assisted semen analysis and loss of membrane integrity evaluated by flow cytometry using PNA/Propidium iodide, starting at 72 h (p < .05) when bacterial counts were 109 CFU/mL. In contrast, bacterial growth in S2 was limited to 1.6 × 103 CFU/mL until 144 h. In S3, bacterial counts were below 10 CFU/mL. In S2 and S3, sperm quality traits did not differ (p > .05) and were maintained throughout 144 h storage about threshold val-ues for useable semen according to the guidelines of the German Livestock Association (BRS e.V.). In conclusion, low-temperature storage of boar semen effectively inhibits the growth of bacteria in-cluding S. marcescens and maintains sperm quality. This is important if effective antibiotics are no longer available, or their use becomes unwanted.


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