Satisfactory breeding potential is transiently eliminated in beef bulls with clinical anaplasmosis

Abstract

Background: Natural service breeding is common in U.S. cow-calf operations. Diseases impacting bull reproductive performance have significant economic consequences for producers. Anaplasmosis may be an underappreciated cause of poor reproductive performance in bulls. The primary systemic effects of bovine anaplasmosis including anemia, fever, and weight loss, can all result in unsatisfactory reproductive performance. The objective of this pilot study was to evaluate breeding soundness examination (BSE) outcomes and clinical changes in bulls during and upon resolution of clinical anaplasmosis. Anaplasma marginale-challenged bulls were observed for clinical disease and infection progression and changes in breeding soundness compared to uninfected control bulls for 16 weeks.

Results: All Anaplasma marginale-challenged bulls were PCR-positive, seropositive, and showed clinical signs by 3-, 17-, and 24-days post-challenge, respectively. Clinical signs of anaplasmosis included pallor, icterus, fever (≥ 40.2 °C), and weight loss. Acute anemia was observed in all challenged bulls with PCV nadirs ≤ 18% and peak percent parasitized erythrocyte ≥ 50%. Decreased scrotal circumference and poor semen quality (e.g., increased percentage of abnormal spermatozoa, decreased progressively motile sperm), were initially observed within days after onset of clinical anaplasmosis signs and continued weeks beyond disease resolution. Control bulls remained negative for A. marginale.

Conclusion: This pilot study demonstrates that clinical anaplasmosis reduces breeding soundness in beef bulls. Anaplasmosis should be considered as a differential for bulls with decreased semen quality, especially within endemic areas. A 90 day or greater retest window is recommended for bulls of unsatisfactory breeding potential recently recovered from clinical anaplasmosis.

Keywords: Anaplasma marginale; Anemia; Breeding Soundness Examination (BSE); Cattle; Fever; Reproduction; Scrotal circumference; Sperm morphology; Sperm motility; Veterinary theriogenology.

Fig. 1

Progression of clinical anaplasmosis in experimentally-challenged beef bulls. Top: Progression of A. marignale bacteremia (A. marginale (Am)/mL blood) evaluated using a quantitative PCR assay targeting the single-copy Msp5 gene. Middle: Changes in packed cell volume (PCV) before, during, and after resolution of clinical anaplasmosis. Bottom: Changes in body temperatures (°C ) prior to, during, and after resolution of clinical anaplasmosis. Figure background shading represents phases of clinical anaplasmosis with Day 0 representing day of A. marginale inoculation in challenged bulls.

Fig. 2

Changes in bull breeding soundness examination parameters over a course of clinical anaplasmosis. Top Body Condition Score (BCS) using a 9-point scale [40]. Middle top: Scrotal circumference (cm). Middle bottom: Percentage of progressively motile spermatozoa. Bottom: Percentage of morphologically normal spermatozoa. Figure background shading represents phases of clinical anaplasmosis with Day 0 representing day of A. marginale inoculation in challenged bulls.

Fig. 3

Abnormal sperm morphologies and other cells in semen samples collected from bulls experimentally-infected withA. marginale. Head Abnormalities: (A) nuclear vacuolation; (B) pyriform head; (C) abnormal free head; Midpiece Abnormalities: (D) distal midpiece reflection (DMR); (E) proximal droplet; (F) DMR; Tail Abnormalities: (G) coiled tail; (H) bent principal piece; (I) distal coil with proximal droplet (midpiece); Other Cells: (J) medusa cell; (I) spermatocyte (immature sperm cell); (J) normal, mature sperm cell.

Fig. 4

Maintenance of satisfactory sperm motility scores in bulls experimentally infected withA. marginale. Semen samples from bulls experimentally infected with A. marginale were assessed for satisfactory (≥ 30% progressively motile sperm) sperm motility compared to time-matched uninfected control bulls. Figure background shading represents disease course of clinical anaplasmosis with Day 0 representing day of A. inoculation in challenged bulls.