Reduced blood flow to peripheral and core body tissues in sheep and cattle induced by endophyte-infected tall fescue

Abstract

Four wethers and 14 steers (environmentally heat stressed, 32 degrees C, 60% relative humidity) were evaluated for changes in blood flow induced by endophyte-infected tall fescue. Concentration of the ergopeptide ergovaline was used as an indicator of diet toxicity due to the endophytic fungus Acremonium coenophialum. Blood flow to specific tissues was measured using radiolabeled microspheres. Wethers received one of two dietary treatments for 30 d before determination of tissue blood flow: 1) a low-endophyte diet (less than .05 ppm ergovaline) or 2) a high-endophyte (1.18 ppm ergovaline) diet. Blood flows to the adrenal glands and skin covering the inner hind leg were less (P less than .10) in wethers consuming the high-endophyte diet than in those consuming the low-endophyte diet. Tissue blood flows in steers were determined on two occasions: 1) after steers had received a low- (less than .01 ppm ergovaline) or high-endophyte (.52 ppm ergovaline) fescue diet for 14 d and 2) 8 d after steers had been switched to a common, fescue-free diet. Blood flows to skin covering the ribs, cerebellum of the brain, duodenum, and colon were less (P less than .10) in steers consuming the high-endophyte diet. However, 8 d after consuming fescue-free diets, steers that had previously consumed the high-endophyte diet had greater (P = .08) blood flow to the coronary bands of the front hooves than steers that had consumed the low-endophyte diet. Blood flows to all other tissues were similar between treatments. We inferred from these experiments that the toxin(s) associated with endophyte-infected tall fescue caused decreased blood flow to peripheral and core body tissues and that this effect was abated within 8 d of removing the toxin(s).

The occurrence of ryegrass staggers and heat stress in sheep grazing ryegrass-endophyte associations with diverse alkaloid profiles

“…The production of high concentrations of epoxy-janthitrems by AR37-infected ryegrass compared with low concentrations of lolitrem B by standard endophyte-infected ryegrass, and the lower severity of ryegrass staggers on AR37-infected ryegrass pastures, indicates that the epoxy-janthitrems are low potency tremorgens compared with lolitrem B, as described by Finch et al (2012). Ingestion of ergovaline, and ergot alkaloids in general, are known to exacerbate heat stress in livestock due to constricting blood flow and therefore reducing the ability of the animal to dissipate heat through the skin (Rhodes et al 1991). Fletcher et al (1999) reported that differences in animals' ability to handle heat stress could be detected without the use of the tunnel house for sheep grazing standard endophyte ryegrass at Lincoln when measured on hot days in the field in summer and autumn.…”

Anti-quality factors associated with alkaloids in eastern temperate pasture

“…Inclusion of the endophyte in fed diets has resulted in increased rectal temperature and respiratory rate. In this regard, the effects of the endophyte were investigated using temperature controlled rooms , Rhodes et al 1991, Osborn et al 1992, Aldrich et al 1993b, Cornell et al 1990). Calves consuming a toxic ryegrass-tall fescue hybrid at increased ambient temperatures had increased rectal temperatures, respiratory rates and depressed body weight gains compared to those fed a non-toxic hybrid ; however, at lower ambient temperatures there were no differences in respiratory rate and rectal temperatures.…”

Journal of Range Management, Volume 54, Number 4 (July 2001)

“…Earlier work (Steen et al 1979, Bond et al 1984 indicated the hematocrit was likely suppressed in cattle grazing E+ tall fescue. In contrast, circulating numbers of red blood cells were not reduced in cattle on endophyte containing diets (Rhodes et al 1991). Since Cu is related to red blood cell production, a Cu deficiency could alter red blood cell parameters.…”

“…Inclusion of the endophyte in fed diets has resulted in increased rectal temperature and respiratory rate. In this regard, the effects of the endophyte were investigated using temperature controlled rooms , Rhodes et al 1991, Osborn et al 1992, Aldrich et al 1993b, Cornell et al 1990). Calves consuming a toxic ryegrass-tall fescue hybrid at increased ambient temperatures had increased rectal temperatures, respiratory rates and depressed body weight gains compared to those fed a non-toxic hybrid ; however, at lower ambient temperatures there were no differences in respiratory rate and rectal temperatures.…”