Research Summary - 4
Seminal bacterial isolates and their associations with semen quality in rams
| Date/Time: |
8/29/2026
16:15
|
| Author: |
Devinda Wickramasingha |
| Clinic: |
LACS, WCVM, University of Saskatchewan |
| City, State, ZIP: |
Saskatoon, SK S7N4S5 |
Devinda Wickramasingha, BVSc, M.Phil, MSc
1
;
Fritz Schumann, BVSc, MVSc
1
;
Matthieu Taillon, BSc, DVM
1
;
Abby Toews, BSc, DVM
1
;
Brooklyn Hunt, BSc
1
;
Kamal Gabadage, BVSc, MVSc, Diplomate ABVP (FA)
1
;
Sarah Parker, BSc, DVM, MVSc
1
;
Dinesh Dadarwal, BVSc, MVSc, PhD, Diplomate ACT
1
;
1Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, S7N 5B4
Introduction:
Despite the routine use of breeding soundness evaluation in rams, little attention has been given to characterizing the bacterial populations residing within ejaculates and understanding how those organisms may compromise the very semen parameters being assessed. This study aimed to characterize common bacterial isolates in ram ejaculates and evaluate their associations with semen quality parameters.
Materials and methods:
A total of 150 rams of various breeds from nine flocks in Saskatchewan underwent breeding soundness evaluation (BSE). Semen was collected by electroejaculation and evaluated for motility, morphology, leukocyte count, and bacterial presence. Samples were cultured for aerobic, anaerobic, and Brucella ovis organisms. Data were analyzed using logistic regression and Wilcoxon rank-sum tests in Stata/BE 17.
Results:
Of the 150 rams evaluated, 88 (59%) had satisfactory semen quality; however, only 57 (38%) passed the BSE, with the remainder failing due to inadequate scrotal circumference (SC). Bacterial isolates were identified in 148 of 150 samples, representing 58 species. The most prevalent isolate was Staphylococcus equorum (43%). Among 95 rams, nine potential reproductive pathogens were identified: Corynebacterium spp. (14.7%), Pasteurella multocida (12%), Streptococcus spp. (11.3%), Brucella ovis (10%), Acinetobacter spp. (10%), Staphylococcus spp. (8%), Trueperella pyogenes (4%), Pseudomonas spp. (2.6%), and Actinobacillus seminis (2.6%). Of these, only B. ovis and Acinetobacter spp. were significantly associated with poor semen quality. B. ovis-positive rams had 9.6 times higher odds of unsatisfactory normal morphology and 6.1 times higher odds of unsatisfactory individual motility. Leukospermia was present in all 15 B. ovis-positive rams, which had 2.5 times higher odds (P<0.001) of having ≥5 leukocytes per high-power field on eosin-nigrosine stain. Acinetobacter spp.-positive rams had lower percentages of normal sperm (48.5% ± 27%), reduced live sperm counts (64.3% ± 13%), and 4.4 times higher odds of unsatisfactory individual motility.
Significance:
These findings reinforce what we already know about B. ovis and semen quality, while drawing attention to Acinetobacter spp. as a potentially underrecognized reproductive pathogen in rams. The association of Acinetobacter spp. with compromised sperm morphology, viability, and motility suggests that bacteriological screening in rams with poor semen quality should look beyond the usual suspects. Practically speaking, finding ≥5 leukocytes per high-power field during a BSE should remain a trigger for B. ovis flock-level screening.
