by Jesse Bussard

This the fourth and final installment of my thesis post series. I promise after this I won’t even dare mention the words, tall fescue, fescue toxicosis, or ergot alkaloids for at least a month! It’s time to discuss my findings briefly and then tell you what all this means for cattle grazing endophyte-infected (E+) tall fescue. If you missed the first three installments in this series, catch up here with Part 1, Part 2, and Part 3.

Myograph Results

• We recorded increasing contractile responses of saphenous veins from steers that previously grazed E+ tall fescue as time-off of E+ pasture increased.
• When compared to the control steers that had grazed bermudagrass, contractile responses of saphenous veins from E+ steers were much lower on the first day of the study.
• By day 63, no difference was seen between contractile responses of either group.

Doppler Ultrasonography Results

• Over time luminal areas of the caudal artery of the tail of E+ steers increased over time. Increases in luminal areas indicate a relaxation or lessening of constriction in blood vessels.
• On the first day of the study, no significant differences were seen between luminal areas of the caudal arteries of either control or E+ steers. It is theorized that this may be due to stress from new environment and the unabated ability of control steers to respond to environmental conditions, unlike E+ steers due to chronic vasoconstriction.
• By day 7 of the study a noticeable difference was seen in lumen areas and by day 35 they were relaxed and similar to those of control steers.

Discussion

Previous studies have show bioaccumulation of ergot alkaloids and a persistence of these compounds to induce sustained contractile responses in saphenous veins. As we hypothesized, contractile responses of saphenous veins from E+ steers were much lower on the first day of the study and increased with time off of pasture. This was due to the effects on adrenergic and serotonergic receptors from chronic exposure to alkaloids. Once removed from the E+ pasture, ergot alkaloid dissipation from cell binding sites on receptors or gradual turnover of alkaloid-receptor complexes may have led to an increased contractility of vascular tissues like was seen in comparing contractile responses of E+ steers to that of control steers on day 63 of the study. While the multimyogrpah is an effect method of testing direct alkaloid effects in the laboratory, it lacks practical in-field application.

The findings of Doppler ultrasonography scans are consistent with those seen in previous studies. When comparison is made of myograph results to those of the Doppler ultrasonography scans, the increasing relaxation and contractility of vessels was similar. These results provide strong evidence indicative of vascular changes seen cattle recovering from fescue toxicosis. While we did not determine if steers did indeed recover completely from ergot alkaloid exposure, results show that the recovery period extends long past the 8 to 10 days previously determined from research on serum prolactin levels in cattle grazing E+ tall fescue.

Conclusions

These results indicate that cattle should be removed from E+ tall fescue pastures for a minimum of 4 to 5 weeks to obtain adequate recovery from ergot alkaloid exposure in cardiovascular tissues and to facilitate a reduction in vasoconstriction and susceptibility to heat stress. A complete clearance of alkaloids from tissues was not determined, therefore more research into this area is needed. Also, recovery from alkaloid exposure could be longer if cattle have greater amounts of bioaccumulation of ergot alkaloids in their vascular system compared to the steers in this study.

It is also clear that Color Doppler ultrasonography has the repeatability to provide objective non-invasive measures of vasoconstriction in cattle induced by ergot alkaloids that is comparable to the mulitmyograph. With it’s non-invasive manner and practibility for in-field application, it will significantly reduce stresses on livestock, labor and resources need to study vascular changes in peripheral tissues of the animal. With future technological advancement, Doppler ultrasonography could provide a useful tool for both researchers and veterinarians as a means to detect severity of symptoms in cattle suffering from fescue toxicosis.

As always, if you have any questions or comments, feel free to leave a comment below or email me (pearlsnapsponderings@gmail.com). I’ll do my best to get you the right answer. Thanks for reading and bearing with me as I review my thesis! I promise the next post on here will have nothing to do with tall fescue!!! In the meantime, keep me in your thoughts. The day I defend all of this is coming on fast (August 30th). Also, I’ll be sure to share the my thesis in it’s entirety when it is officially approved and published by the graduate school.