Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 2/23/2007
Publication Date: 7/8/2007
Citation: Klotz, J.L., Brown, K.R., Matthews, J.C., Boling, J.A., Bush, L.P., Strickland, J.R. 2007. Grazing High Versus Low Endophyte-Infected Tall Fescue Reduces Contractility of Bovine Lateral Saphenous Veins. J. Anim. Sci. Vol. 85, Suppl. 1/J. Dairy Scit. Vol. 90, SUppl. 1/Poult. Sci. Vol. 86 Suppl 1. pg 12-13. Interpretive Summary:
Technical Abstract: Cattle that graze toxic endophyte-infected tall fescue are continuously exposed to a myriad of toxins that are known to negatively affect cardiovascular tissues. As part of a larger study documenting the physiologic impact of grazing endophyte-infected tall fescue in growing cattle, the objective was to examine the vasoconstrictive activities of 5-hydroxytryptamine (5HT), '-methylserotonin (ME5HT; a 5HT2 receptor agonist), D-lysergic acid (LSA), and ergovaline (ERV) as affected by consumption of 2 levels of toxic endophyte infected tall fescue. Segments (2-3 cm) of the cranial branch of lateral saphenous vein were collected at time of slaughter from steers following an 89-105 d grazing period of either a low endophyte-infected (LE) mixed grass pasture (6.8% infection; n=8; BW=336'9 kg) or a high endophyte-infected (HE) tall fescue pasture (62.8% infection; n=8; BW=317'9 kg). Veins were sliced into 2-3 mm sections and suspended in a myograph chamber containing 5 mL of oxygenated Krebs-Henseleit buffer (95% O2/5%CO2; pH=7.4; 37'C) and allowed to equilibrate at 1 g of tension for 90 min. Increasing concentrations (1x10-11 to 1x10-4 M) of 5HT, ME5HT, LSA, and ERV (1x10-11 to 1x10-4 M) were administered every 15 min. Data were normalized (%) to contractile response induced by a reference dose of norepinephrine (1x10-4 M) and data for each treatment were analyzed for effects of concentration and endophyte level. Maximal contractile intensities (1x10-4 M) were greater (P<0.05) for steers grazing LE pastures than HE pastures for 5HT (73.3 vs 48.9'2.1%), ME5HT (52.7 vs 24.9'1.5%), and ERV (65.7 vs 49.1'2.6%). Onset of contractile response did not differ for 5HT and ERV, but onset of ME5HT contraction was delayed (P<0.05) in HE steers to 10-4 compared to 10-5 M in LE grazing steers. Grazing of HE pastures for 89-105 d appears to induce functional alterations in blood vessels, as evidenced by reduced contractile capacity and altered serotonergic receptor activity.