Feeding yearling Angus bulls low-level ergot daily for 9 weeks decreased serum prolactin concentrations and had subtle effects on sperm end points
Citation
Chohan, M.R., Munro, B.J., Cowan, V.E., Anzar, M., Blakley, B., McKinnon, J., Kastelic, J.P., Rivera-Acuña, F., Singh, J. (2021). Feeding yearling Angus bulls low-level ergot daily for 9 weeks decreased serum prolactin concentrations and had subtle effects on sperm end points. Theriogenology, [online] 161 187-199. http://dx.doi.org/10.1016/j.theriogenology.2020.11.025
Plain language summary
Canadian Food Inspection Agency standards permit 2 to 3 mg/kg ergot alkaloids in animal feed. This study investigated effects of feeding the upper permissible limit of ergot alkaloids (3.4 mg/kg of dry matter intake) for a 9 wk period during the spring season on semen quality, sperm structural parameters and prolactin concentrations in yearling bulls. Plasma prolactin concentrations decreased by 4-fold in the ergot-fed bulls during the exposure period. Since the present study was designed to encompass reproductive maturation, age-related expected improvements in body weight, scrotal circumference, sperm counts, progressively motility, and sperm velocities, along with decreasing trends in sperm defects, were recorded. The scrotal circumference was smaller by 2.7% in ergot-treated yearling bulls (averaged over exposure and post-exposure duration). The majority of sperm end points were not affected by this concentration of ergot in feed. However, there were the following ergot-specific changes: 1) small decrease in progressive sperm motility from the exposure to the post-exposure period, in contrast to an expected increasing trend observed in the reference group; 2) a minor decrease in straight-line sperm velocity from the exposure to post-exposure periods in the ergot group, compared to an increase in the control group; 3) continuation of midpiece defects in the first half of the post-exposure period as compared to a progressive decrease in the placebo group; 4) increase in percentage of sperm with principal piece defects from exposure to the post-exposure periods was greater for the ergot group; and 5) a relative decrease in the proportion of sperm with medium mitochondrial membrane potential during exposure and post-exposure periods. The progressive increase in body weight and scrotal circumference was similar in both treated and un-treated yearling bulls and body temperature was maintained during and after ergot exposure. Overall, the present results supported our hypothesis that ergot alkaloids at low-levels markedly decrease plasma prolactin concentrations in yearling bulls. Prolactin concentrations appeared to recover somewhat in the 2-mo period after ergot feeding. Our second hypothesis related to ergot effects on semen quality and sperm characteristics was partially supported. Recorded semen effects were subtle, and it remains to be determined whether these changes affect bull fertility.
Abstract
Our objective was to determine whether feeding yearling bulls with the higher recommended Canadian limit of ergot alkaloids (∼3 mg/kg dry matter intake, DMI) would affect sperm characteristics and plasma prolactin concentrations. Aberdeen Angus bulls (12–13 mo old, n = 7/group) allocated by blocking for sperm concentration and body weight, were fed placebo or ergot alkaloids in gelatin capsules (60 μg/kg body weight daily, 3.4 mg/kg of DMI) for 9 wk. Semen samples were collected weekly by electroejaculation and examined with a computer assisted semen analyzer (CASA) and flow cytometry, for the intervals 5 wk before (Pre-exposure period), 9 wk during (Exposure period) and 9 wk after (Post-exposure period) treatment. Weekly plasma samples were analyzed for prolactin by radioimmunoassay. Plasma prolactin concentrations decreased markedly (mean ± SEM, 16.74 ± 3.70 in Exposure and 33.42 ± 3.08 ng/mL in Post-Exposure periods; P < 0.01) compared to Control (67.54 ± 21.47 and 42.59 ± 15.06 ng/mL). Treatment did not affect (P ≥ 0.17) body weight gain, sperm concentration, sperm count/ejaculate, motility or percent live sperm. Averaged over the exposure and post-exposure durations, the scrotal circumference was smaller (P = 0.02) by 2.7% in the Ergot group. Progressive motility remained unchanged from 59.92 ± 2.31% in Exposure to 59.61 ± 2.59% in Post-Exposure periods, compared to marked increase in Control (61.42 ± 1.60% to 67.52 ± 1.47%; P = 0.02). Straight-line sperm velocity decreased (−3.15 ± 1.53 μm/s) from exposure to post-exposure periods in Ergot group (P = 0.04) versus an increase (2.96 ± 2.17 μm/s) in Control. Midpiece defects decreased from Exposure to Post-exposure periods in Control group but remained unchanged in Ergot group (trt∗age, P < 0.01). Ergot feeding resulted in a smaller proportion of sperm with medium mitochondrial potential (Ergot: 22.65 ± 0.98%, Control: 24.35 ± 1.05%, P = 0.04). In conclusion, feeding ergot at Canadian permissible limit for 9-wk resulted in a 4-fold decrease in plasma prolactin concentrations. Semen end points were not significantly affected, although there were subtle effects on progressive motility, midpiece defects and mitochondrial membrane potential. Clinical relevance of observed changes requires further evaluation. Results supported our hypothesis that prolonged low-level ergot will adversely affect plasma prolactin. However, semen parameters were partially affected, supporting similar work on fescue toxicosis.