Location: Forage-animal Production ResearchTitle: Red clover dosed in loose mineral mitigates vasoconstriction in steers challenged with E+ tall fescue seed
Submitted to: American Forage and Grassland Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 11/6/2019
Publication Date: 1/5/2020
Citation: Harlow, B.E., Johns, J.T., Flythe, M.D. 2020. Red clover dosed in loose mineral mitigates vasoconstriction in steers challenged with E+ tall fescue seed. American Forage and Grassland Conference Proceedings. 1:12.
Technical Abstract: Endophyte-infected (E+) tall fescue can cause persistent vasoconstriction in ruminants and consequently fescue toxicosis. Legumes, including red clover (RC), contain isoflavones that are known hypotensive agents. Previous experiments have shown the benefits of RC (pasture or hay at 15 – 30% of the diet) on blood flow and growth performance of cattle grazing E+ tall fescue. However, the minimum level of RC supplementation to elicit vascular benefits has not been identified. The objective of this study was to determine if low levels of RC in conventional loose mineral could mitigate vasoconstriction associated with E+ tall fescue seed challenge. Rumen fistulated steers (n = 12) received 1 of 4 treatments: 1) control mineral (6 oz head d-1; n = 3), 2) 10% RC mineral (n = 3), 3) 15% RC mineral, or 4) 20% RC mineral. All fistulated steers were first adapted to a high fiber diet for 2 weeks ad libitum and then were subjected to a 2-week E+ seed challenge. The caudal artery of each steer was imaged repeatedly over the course of the study using Doppler ultrasonography to monitor artery luminal areas. The E+ seed challenge induced vasoconstriction in control steers receiving conventional loose mineral. Both 10% and 15% RC mineral treatments did not reliably mitigate vasoconstriction associated with E+ seed challenge. However, 20% RC mineral steers remained dilated and were unaffected by the E+ seed challenge. These results indicate that 20% RC mineral could be used to mitigate vasoconstriction associated with tall fescue toxicosis. Future field research is needed to evaluate the efficacy of 20% RC mineral in cattle grazing E+ tall fescue pastures.