Boar semen bacterial contamination in Italy and antibiotic efficacy in a modified extender.

The aims of the study were to identify microbial flora in boar semen under field conditions in northern Italy, to investigate antibiotic resistance and sensitivity of isolated bacteria, and to evaluate elimination of bacteria after storage in two types of extenders added with different antibiotics (amikacin vs gentamicin). A total of 60 boars were collected in 13 pig farms. Bacteriological and mycological investigations were performed immediately on raw semen samples, then at 48 and 120 h of storage on semen diluted randomly in a new short-term modified extender (ME-S) or in a commercial one (CRONOSTM). Bacterial contamination was found in 63% of raw semen samples and different bacterial species were isolated: E.coli, Serratia marcescens, Staphylococcus epidermidis and aureus, Proteus spp., Streptococcus spp. and Pseudomonas aeruginosa. E. coli was the most isolated contaminant (53%); Pseudomonas aeruginosa was found only in one semen sample. The analysis of variance of factors affecting contamination levels was significant for the farm of origin (P<0.05) and not significant for the breed. Antibiotic resistance of these bacteria was assessed using different antibiotics. Significant differences (P<0.05) between observed and expected frequencies of bacterial isolates resistant or not to the antibiotics contained in the extenders were found. At 48 h of storage a reduction of aerobic contamination was found after ME-S dilution by 85.3% and after CRONOSTM by 63.8%. This paper proved the presence of pathogenic bacteria in semen. We thus believe it is highly advisable to perform periodic microbiological screening of boar semen in the swine industry to avoid the use of low sperm quality. [ABSTRACT FROM AUTHOR]