Location: Forage-animal Production ResearchTitle: Vasoconstrictive responses of lambs grazing endophyte-infected perennial ryegrass paddocks Author
Submitted to: International Symposium on Fungal Endophytes of Grasses
Publication Type: Abstract Only
Publication Acceptance Date: 6/4/2010
Publication Date: 6/28/2010
Citation: Aiken, G.E., Sutherland, L., Fletcher, L. 2010. Vasoconstrictive responses of lambs grazing endophyte-infected perennial ryegrass paddocks. International Symposium on Fungal Endophytes of Grasses. pp 3-4. Interpretive Summary:
Technical Abstract: The AR6 novel endophyte (Neotyphodium lolii) produces ergovaline that deters against the African black beetle, but also causes vasoconstriction that restricts an animal’s ability to dissipate body heat. An experiment was conducted with 3, 0.10-ha pastures of ‘Extreme’ perennial ryegrass (Lolium perenne L.) to compare vasoconstrictive responses in ewe lambs grazing pastures infected with AR6 (n = 5 lambs), wild-type (WT; n = 6), which produces ergovaline, or endophyte-free (Nil; n = 5) for 14 days. A second phase was conducted to evaluate vasoconstrictive responses after switching AR6 lambs to Nil, and Nil lambs to AR6. Cross-sectional lumen area of the left auricular artery was measured using ultrasonography on days 13, 15, and 18 in phase 1 and on days 2, 4, 7, and 9 in phase 2. Urine was collected on the first and fourth day of phase 2 for determining urinary lysergol/creatinine ratios. Lambs in phase 2 were heat challenged (32.5°C) in an environmental chamber on day 19. Lumen areas in phase 1 were less (P < 0.05) for AR6 and WT than for Nil. Lumen areas increased linearly (P < 0.05) over time after AR6 lambs were switched to Nil, and tended (P = 0.11) to decrease linearly in lambs switched from Nil to AR6. Between days 1 and 4 in phase 2, urinary lysergol/creatinine ratios for AR6 lambs switched to Nil decreased (P < 0.001) from 3.6 to 1.6 and Nil lambs switched to AR6 increased (P < 0.001) from 0 to 3.0. There were no differences among treatments in rectal temperatures or respiration rates during the heat challenge. Results indicated a rapid vasoconstrictive response in lambs exposed to ergovaline. Although vasoconstriction was eased after AR6 lambs were placed on Nil, but lack of physiological adjustment to the heat challenge indicated ergovaline remained in the vasculature.