Bacterial prevalence in equine semen

Abstract

Stallion semen contains a high prevalence of contaminating bacteria from the external genitalia during collection (Rota et al., Theriogenology 2011;76:464-70). These bacteria can induce endometritis in mares predisposed to infections after insemination and can have a deleterious effect on the quality of preserved sperm, affecting their viability and fertility (Samper & Tibary, Theriogenology 2006;66:551-9). In addition, some reports have demonstrated the detrimental effects of some bacteria, such as Pseudomonas aeruginosa or Streptococcus equisimilis on the motility and membrane integrity of equine sperm (Aurich & Spergser, Theriogenology 2007;67:912-8). This study aimed to assess bacterial and fungal prevalence in semen from Mangalarga Marchador stallions. Eight stallions were evaluated at random at different stud farms in the state of Rio de Janeiro, Brazil. After washing the penis with water, semen was collected using a Hannover model artificial vagina. A swab was then submerged in the semen, preserved, transported, and refrigerated in Stuart medium until it was sent to the reproduction laboratory. After incubation for 24 hours at 37°C, bacterial plating was carried out on blood agar, MacConkey agar and Chromagar, and fungal plating on Sabouraud medium. After 24 hours of culture, identification was made by morphology and Gram staining. Of the eight stallions evaluated, five (63%) had bacteria in their semen. The bacteria found were Streptococcus spp., Escherichia coli, and Klebsiella spp. (Scholtz et al., Equine Vet J. 2024;1–11). Streptococcus spp. was isolated in 50% of the stallions (4/8), Escherichia coli in 38% (3/8) and Klebsiella sp. in 13 % (1/8) of the samples. Mixed bacterial growth was identified in 38% (3/8) of the samples, two of them were Streptococcus spp. and Escherichia coli and one Streptococcus sp. and Klebsiella sp, respectively. There was no fungal growth in the samples analyzed. Our results are compatible with the bacterial isolates found in a study carried out in Sweden with a total bacterial prevalence of 59%, 53% being Klebsiella pneumoniae, 80% beta-haemolytic Streptococcus and 43% Pseudomonas aeruginosa (Al-Kass, et al, Acta Veterinaria Scandinavica, 2019). It is concluded that bacterial presence in stallion semen should be investigated before it is used in the breeding season.