Abstract
Ergot alkaloids have been associated with decreased livestock reproductive rates. Concentration of alkaloids in the reproductive tract after consumption of toxic forage is unknown. In addition, the direct effects of alkaloids on bovine spermatozoa have not been determined. We investigated the direct and interactive effects of 3 ergot alkaloids (ergotamine, dihydroergotamine, and ergonovine) on motility of frozen–thawed bovine spermatozoa. Thawed spermatozoa from 3 bulls were pooled and washed using a Percoll density gradient. Sperm motility was visually estimated by counting at least 100 spermatozoa in each triplicate well (> 300 per treatment per replicate). The cell counting was conducted using phase contrast (400�) on an inverted bright field microscope. Spermatozoa were considered motile if they exhibited free progressive forward or other movement and were not attached to the well surface. Motile spermatozoa were exposed to alkaloids ranging in concentration from 0 to 100 �M. Assays were conducted in modified sperm-TL (mSPTL) medium at 39�C in moist air without CO2 for 6 to 12 h. The results showed that both ergotamine (ET) and dihydroergotamine (DHET) inhibited (P < 0.05) sperm motility at concentrations greater than 50 �M and 33.3 �M, respectively. Ergonovine (EN) did not inhibit sperm motility at the test concentrations. Inhibitory effects of alkaloids on sperm motility were concentration-dependent for ET and DHET incubations and time-dependent for DHET incubations. Sperm motility also was inhibited by an interaction (P < 0.05) between ET and DHET at concentrations of 16.7 �M or above. The medium pH affected the toxic effects of both ET and DHET, whereas the medium osmolarity affected only the toxic effect of ET on relative sperm motility (P < 0.05). Medium osmolarity of 358 mOsm and/or pH higher than 7.1 exacerbated the toxic effects of the alkaloids. These results demonstrate that ergot alkaloids can directly interact with spermatozoa and impair sperm motility. Herbivores consuming toxic tall fescue are exposed to a cocktail of ergot alkaloids. Alkaloid interactive effects coupled with altered cell chemistry, due to increased respiration rates and frequent urination, on spermatozoa may indicate the mechanism by which reproduction is impaired in animals consuming toxic forage.
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