Tasco-Forage: II. Monocyte immune cell response and performance of beef steers grazing tall fescue treated with a seaweed extract

Effects of applying Tasco-Forage, an Ascophyllum nodosum seaweed-based prod uct prepared by a proprietary process, to endophyte (Neotyphodium coenophia lum [Morgan-Jones and Gams] Glenn, Bacon, and Hanlin)-infected and endophyt e-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 Vi rginia 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 (S D = 8) and 250 kg (SD = 2) in yr 2 and 3, respectively. Tasco (3.4 kg/ha) w as dissolved in water and applied to pastures in April before grazing was b egun and again in July at the same rate. The grazing period was from mid-Ap ril to late September or mid-October. Total gains were higher (P < 0.05) fo r steers grazing uninfected than for those grazing endophyte-infected tall fescue. Rectal temperatures were increased (P < 0.05) due to endophyte infe ction at both locations; Tasco application decreased temperature of steers grazing infected fescue in Virginia (interaction, P < 0.07) but increased t emperatures of steers grazing infected fescue in Mississippi (interaction, P < 0.05). Presence of the endophyte resulted in rough hair coats and loss of hair color, but the effect was partially offset (P < 0.05) by Tasco appl ication in Virginia in 1995. Both monocyte phagocytic activity (all years a nd locations) and major histocompatibility complex class II expression (199 5 only) were decreased (P < 0.05) in steers due to endophyte infection, but this effect was reversed (P < 0.05) by application of Tasco to pastures. A pplication of the extract from A. nodosum seems to have use in alleviating adverse effects of endophyte on immune function and may improve hair coat c ondition in cattle grazing infected fescue, but effects on rectal temperatu re varied due to location.