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The possibility of supplementing livestock diets with an aluminosilicate to protect them from fescue toxicosis was investigated. An in vitro study showed that hydrated sodium calcium aluminosilicate (HSCAS) removed greater than 90% of the ergotamine from aqueous solutions at pH 7.8 or lower, indicating a high affinity of ergotamine for HSCAS in vitro. Rats fed diets containing tall fescue seed infested (E+) with the endophytic fungus Acremonium coenophialum had lower (P less than .05) feed intakes and weight gains than did rats fed diets containing uninfested (E-) tall fescue seed. When feed intake by rats fed the E- seed diet was limited to that of rats fed the E+ seed diet, weight gains did not differ, but testes weights and serum prolactin (PRL) concentrations were lower (P less than .05 and .10, respectively) in rats receiving E+ seed. Supplementing E+ seed diets with HSCAS did not eliminate effects of E+ seed on intake, PRL, or testes weights. Sheep fed E+ tall fescue hay had higher (P less than .05) rectal temperatures than did sheep fed an equal amount of E- tall fescue hay, but OM and N digestion coefficients did not differ between the two hays. Supplementing E+ hay diets with HSCAS did not eliminate the effect of E+ hay on rectal temperatures. Addition of 2% HSCAS to tall fescue hay diets did not affect apparent absorption by sheep of OM, N, Ca, P, Na, K, or Cu, but it reduced (P less than .05) the apparent absorption of Mg, Mn, and Zn.(ABSTRACT TRUNCATED AT 250 WORDS)

A 3‐yr study was conducted at Ames Plantation, Grand Junction, TN to determine the effects of fungal endophyte (Acremonium conenophialum Morgan‐Jones & Gams) infestation (E+) levels in ‘Kentucky 31’ tall fescue (Festuca arundinacea Schreb.) pastures on steer (Bos taurus L.) performance. Two replications were used of 1.2‐ha pastures overseeded yearly with ladino white clover (Trifolium repens L.) on a fine‐silty, mixed, thermic Typic Hapludalf soil. Yearling tester steers (three per pasture) and additional steers of similar size maintained available forage at heights of 2.5 to 7.5 an. Botanical composition, available forage, average daily gain (ADG), grazing days, and gain per hectare were determined every 21 d; serum prolactin, haircoat roughness, rectal temperatures, and E+ levels were measured at longer intervals. Results were computed using a generalized linear mixed models procedure. Generalized least squares means and standard errors for the broad inference space were estimated (BLUE) and differences for specific linear contrasts were predicted (BLUP). Steer ADG was depressed from over 800 to about 450 g in spring and from about 700 to 400 g during the entire grazing season as A. coenophialum increased from 3 to 81%. Animal grazing days were not different among treatments. Gain was about 65 kg ha−1 more with 22% E+ (379 kg ha−1) than at higher endophyte levels, but it was almost 500 kg ha−1 at 3% E+. Serum prolactin (125 ng mL−1 in steers grazing 3% E+) was halved with 22% E+ and was depressed further at higher E+ levels (41 to 18 ng mL−1). Results suggested that the effect of the endophyte on animal performance in tall fescue‐clover pastures is not linear, with greater depression per unit infestation at lower levels than at higher levels.

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