|Sutherland, B. Lee -|
|Fletcher, Lester -|
Submitted to: New Zealand Veterinary Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 16, 2011
Publication Date: July 1, 2011
Citation: Aiken, G.E., Sutherland, B., Fletcher, L.R. 2011. Haemodynamics of lambs grazing perennial ryegrass (Lolium perenne L.) either infected with AR6 novel wild-type endophyte or not infected. New Zealand Veterinary Journal. 59(4):179-184. Interpretive Summary: A wild-type (WT) endophyte (Neotyphodium Lolii) infects perennial ryegrass (Lolium perenne L.) and produces alkaloids that enhance plant persistence and productivity, but also produces lolitrem B, which can cause ryegrass staggers. This malady places a heavy cost burden on the health and production of livestock in New Zealand. New Zealand AgResearch Ltd. has developed novel endophytes that do not produce lolitrem B, but do produce alkaloids that provide insect deterrence. One such novel endophyte, AR6, produces peramine and ergovaline to control the Argentine stem weevil and African black beetle. This endophyte has potential to substantially improve persistence and forage production of perennial ryegrass pastures while alleviating ryegrass staggers. However, ergovaline produced by the AR6 endophyte has been implicated as a potent vasoconstrictor produced by the wild-type endophyte that infects tall fescue and causes severe heat stress in warm and humid environments. A grazing experiment was conducted to evaluate vasoconstriction of the auricular artery and blood flow resistance in the carotid artery in ewe lambs grazing perennial ryegrass infected with AR6 or wild type endophytes, or was Nil (endophyte-free). Vasoconsrtiction and blood flow resistance were measured using color Doppler ultrasonography. Vasoconstriction and blood flow resistance were greater in lambs grazing AR6 and WT perennial ryegrass that those grazing Nil, and the responses tended to be greater for AR6 than for WT lambs. Results clearly indicated a vulnerability to heat stress for sheep grazing perennial ryegrass infected with AR6 and WT endophytes, which would be of major concern to sheep producers in warmer environments of the New Zealand North Island.
Technical Abstract: Coopworth ewe lambs were randomly assigned to 3, 0.10-ha pastures of ‘Extreme’ perennial ryegrass that were infected with the AR6 novel endophyte (AR6; n=5), infected with the wild-type endophyte (WT; n=6), or was endophyte-free (Nil; n=5). Lambs were conditioned to the pastures from 25 Feb. to 16 Mar., 2009 (19 days of grazing). An experimental phase was initiated by switching lambs from the AR6 to the Nil pasture, switching those on Nil to the AR6 pasture (Nil/AR6), or having lambs remain on WT ryegrass as a control. Grazing for the experimental phase was for 18 days. Color Doppler ultrasonography was used to monitor lumen (cross-sectional) area of the auricular artery as a measure of vasoconstriction, and was used to measure pulsatility indices, heart rate, systolic and diastolic velocities, and mean velocity in the carotid artery. Urine was sampled once during each phase to measure urinary alkaloids. Vasoconstiction was detected in the auricular arteries of lambs grazing AR6 and WT pastures. Lumen areas in auricular arteries linearly declined after the lambs grazed on Nil were switched to the AR6 pasture, and these areas increased linearly over time after AR6 lambs were switched to Nil pastures. Resistance to blood flow in the carotid decreased linearly after lambs on AR6 were switched to the Nil pasture and there was a tendency for blood flow resistance to increase after Nil lambs were switched to the AR6 pasture. Vasoconstriction and blood flow resistance was generally stronger in lambs grazing AR6 than those grazing WT pasture. Urinary alkaloids for AR6 lambs decreased after they were switched to Nil pastures, whereas for Nil lambs they increased after these lambs were switched to the AR6 pasture. Results indicate a potential vulnerability to heat stress for lambs grazed on perennial ryegrass infected with the AR6 novel or WT endophytes, but this vulnerability is reduced over time after lambs are switched from AR6 or WT to Nil pastures.