SUMMARY Caecal fluid samples collected 8 and 24 hours after carbohydrate overload were quantitatively compared to control samples in terms of aerobic and anaerobic bacteria. Concomitant increases in lactic acid‐producing bacteria and decreases in Gram negative bacteria were substantiated during the onset of acute laminitis. Progressive decreases in caecal fluid pH were also quantitated. Although endotoxin assays of caecal fluid and blood were not done, the caecal flora changes suggest its presence during the onset of acute laminitis. RÉSUMÉ Des échantillons de fluide coecal recueillis 8 et 24 heures apràs une surcharge digestive en hydrates de carbone furent comparés à des échantillons témoins pour apprécier les modifications de la flore aérobie et anaérobie. On constata une augmentation des bactéries productrices d'acide lactique et une diminution des bactéries Gram—avec installation des signes de fourbure aigue. Une diminution progressive du Ph du liquide coecal fut également remarquée. On ne contrôla point la présence d'antoxines dans le liquide coecal ni dans le sang. Mais les variations de la flore coecale laissent penser à l'existence de telles toxines au début de la fourbure aigue. ZUSAMMENFASSUNG Blinddarminhalt wurde 8 und 24 Stunden nach Kohlenhydratüberfütterung entnommen und quantitativ verglichen mit Kontrollproben (Zahl der aeroben und anaeroben Bakterien). Beim Eintritt einer akuten Hufrehe kommt es gleichzeitig zu einer Vermehrung von Lactat‐produzierenden Bakterien und zu einer Verminderung von Gram‐negativen Keimen. Ein zunehmender Abfall des pH im Blindarminhalt konnte ebenfalls quantitativ erhärtet werden. Obgleich Endotoxinbestimmungen in der Blinddarmflüssigkeit und im Blut nicht vorgenommen werden konnten, kann das Vorhandensein von Endotoxin aufgrund der Veränderungen der Flora beim Eintritt einer akuten Rehe vermutet werden.

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).

Summary Thirteen (65 per cent) of 20 horses subjected to carbohydrate overload developed Obel Grade 3 lameness within 56 h. Increases in plasma endotoxin from control levels of less than 0.1 ng/litre to values ranging from 2.4 to 81.53 ng/litre were measured in 11 (85 per cent) of 13 horses during the onset of Obel Grade 3 lameness. Obel Grade 3 lameness was associated with rises in plasma Gram‐negative endotoxin levels in 11 (92 per cent) of 12 horses. Two peak increases separated by 16 h were verified in five (45 per cent) of 11 horses that exhibited both endotoxaemia and Obel Grade 3 lameness. The first peak occurred, on average, at 32 h and (he second peak at 48 h post overload when only one peak was measured, this occurred in four horses at the average time of 24 h whereas in another three horses only a 48 h or 56 h peak was detected after carbohydrate overload.

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