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Effects of applying Tasco-Forage, an Ascophyllum nodosum seaweed-based product prepared by a proprietary process, to endophyte (Neotyphodium coenophialum [Morgan-Jones and Gams] Glenn, Bacon, and Hanlin)-infected and endophyte-free tall fescue (Festuca arundinacea Schreb.) were studied in each of 3 yr (1995, 1996, and 1997) in Virginia and in 1996 and 1997 in Mississippi. There were 48 steers at each location in each year (n = 240) in a 2 x 2 x 2 factorial arrangement with two replications at each location. Steers in Virginia were Angus and Angus x Hereford with initial weights of 245 kg (SD = 20), 234 kg (SD = 9), and 265 kg (SD = 5) in yr 1, 2, and 3, respectively. Steers in Mississippi were 3/4 Angus and 1/4 Brahman and weighed 230 kg (SD = 8) and 250 kg (SD = 2) in yr 2 and 3, respectively. Tasco (3.4 kg/ha) was dissolved in water and applied to pastures in April before grazing was begun and again in July at the same rate. The grazing period was from mid-April to late September or mid-October. Total gains were higher (P [is less than] 0.05) for steers grazing uninfected than for those grazing endophyte-infected tall fescue. Rectal temperatures were increased (P [is less than] 0.05) due to endophyte infection at both locations; Tasco application decreased temperature of steers grazing infected fescue in Virginia (interaction, P [is less than] 0.07) but increased temperatures of steers grazing infected fescue in Mississippi (interaction, P [is less than] 0.05). Presence of the endophyte resulted in rough hair coats and loss of hair color, but the effect was partially offset (P [is less than] 0.05) by Tasco application in Virginia in 1995. Both monocyte phagocytic activity (all years and locations) and major histocompatibility complex class II expression (1995 only) were decreased (P [is less than] 0.05) in steers due to endophyte infection, but this effect was reversed (P [is less than] 0.05) by application of Tasco to pastures. Application of the extract from A. nodosum seems to have use in alleviating adverse effects of endophyte on immune function and may improve hair coat condition in cattle grazing infected fescue, but effects on rectal temperature varied due to location. Key Words: Festuca, Forage, Grazing, Immune Response, Steers, Toxicity

Tall fescue (Festuca arundinacea Schreb.) infected with the endophyte Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon, and Hanlin) causes fescue toxicosis in cattle grazing the forage, but effects of the endophyte were considered to be abated soon after removal of the animals from pastures. Tasco-Forage, a proprietary extract from the brown seaweed Ascophyllum nodosum, is a known source of cytokinins and has increased antioxidant activity in both plants and the animals that graze the forage. Tasco was applied at 0 and 3.4 kg/ha to infected and uninfected tall fescue pastures in Virginia and Mississippi. Forty-eight steers grazed the pastures at each location during each of 2 yr (n = 192) before being transported to Texas for feedlot finishing. On arrival at the feedlot, steers from Tasco-treated pastures had higher (P [is less than] 0.01) monocyte phagocytic activity and tended (P [is less than] .0.07) to have higher major histocompatibility complex class II expression than steers that grazed the untreated pastures. A depression (P [is less than] 0.05) in monocyte immune cell function due to grazing infected fescue was detected throughout the feedlot finishing period but was reversed by Tasco. Rectal temperatures were elevated (P [is less than] 0.07) in steers that had grazed the infected tall fescue when they arrived in Texas, but by d 14 no difference was detected. However, by d 28 the temperature effects of infected tall fescue were reversed. Steers that had grazed infected fescue had lower (P [is less than] 0.01) rectal temperatures on d 112 of the feedlot period, demonstrating a much longer-lasting effect of the endophyte on thermoregulatory mechanisms than previously thought. Steers that had grazed Tasco-treated pastures had higher (P [is less than] 0.01) rectal temperatures on d 56 than steers that had grazed untreated fescue. Steers that had grazed the Tasco-treated pastures had higher marbling scores (P [is less than] 0.05) regardless of the endophyte, but no effect of Tasco or endophyte on gain was measured. Our data suggest that Tasco application to tall fescue pastures alleviated some of the negative effects of tall fescue toxicity. Key Words: Beef, Carcass Characteristics, Endophytes, Immune Response