Bacterial contamination of boar semen affects the litter size

One hundred and fifteen semen samples were collected from 115 different boars from two farms in Cuba. The boars belonged to five different breeds. Evaluation of the semen sample characteristics (volume, pH, colour, smell, motility of sperm cells) revealed that they meet international standards. The samples were also tested for the presence of agglutinated sperm cells and for bacterial contamination. Seventy five percent of the ejaculates were contaminated with at least one type of bacteria and E. coli was by far the major contaminant, being present in 79% of the contaminated semen samples (n = 68). Other contaminating bacteria belonged to the genera Proteus (n = 31), Serratia (n = 31), Enterobacter (n = 24), Klebsiella (n = 12), Staphylococcus (n = 10), Streptococcus (n = 8) and Pseudomonas (n = 7). Only in one sample anaerobic bacteria were detected. Pearson's analysis of the data revealed that there is a positive correlation between the presence of E. coli and sperm agglutination, and a negative correlation between sperm agglutination and litter size. One-way ANOVA and post hoc Tukey analysis of 378 litters showed that the litter size is significantly reduced when semen is used that is contaminated with spermagglutinating E. coli above a threshold value of 3.5 × 103 CFU/ml.