The dominant cool-season forage in the southeastern United States is the tall fescue cultivar Kentucky 31 (KY31). Kentucky 31 possesses an endophyte which produces a family of toxins called ergot alkaloids. These toxins negatively affect the physiology of animals upon consumption. While the literature is clear that these toxins affect body weight, body temperature, blood flow and hair growth, their effect on bulls’ reproductive biology is not well defined. We conducted four experiments evaluating semen quality and fertility of young beef bulls exposed to ergot alkaloids.
In Experiment 1, bulls were fed concentrate diets with or without ergot alkaloids for 126 days. All bulls were sacrificed at the end of the 126-day feeding trial or 60 days after removal from treatment. In Experiments 2 through 4, bulls were grazed on KY31 or a novel endophyte-infected tall fescue, which does not produce ergot alkaloids. Tissues obtained in Experiment 1 were subjected to end point RT-PCR and immuno-histochemistry using primers and antibodies specific for prolactin, dopamine and serotonin receptors. In all experiments, semen evaluations were conducted periodically. For Experiments 3 and 4, semen was extended and used to time AI cows to assess fertility.
Semen quality did not differ in Experiment 1 for all variables examined.
- We identified the presence of prolactin receptor, dopamine and serotonin receptors in the testes, epididymis and on sperm cells.
- The prolactin receptor mRNA abundance was decreased in testis samples due to ergot alkaloid treatment at both slaughter dates.
- Using seminal fluid samples obtained from bulls in Experiments 1 and 2 and subjecting the samples to RIA, we found that prolactin is present in seminal fluid with concentrations in bulls grazing KY31 lower than those grazing NE, but no difference in seminal fluid prolactin concentrations were observed for Experiment 1.
- Further, bulls grazing KY31 in Experiment 2 exhibited a decrease in sperm cell morphology not observed in Experiment 1.
- Day 35 timed AI pregnancy rates for Experiment 3 were reduced for the KY31 treatment; however, no difference due to treatment was observed in Experiment 4.
These data tend to indicate that semen quality and fertility are altered when grazing KY31; however, these observations may be due to toxin by nutrition level interactions.