GROWTH AND SUBSEQUENT FEEDLOT PERFORMANCE OF ESTRADIOL-IMPLANTED VS NONIMPLANTED STEERS GRAZING FALL-ACCUMULATED ENDOPHYTE-INFESTED OR LOW-ENDOPHYTE TALL FESCUE

A growing-finishing study using Angus steer calves was conducted in th ree phases: 1) grazing stockpiled 'Kentucky-31' tall fescue (Festuca a rundinacea Schreb.) with high (65%; HE KY-31) and low (0%; LE KY-31) i nfestation rates of Acremonium coenophialum Morgan-Jones and Gams and 'Kenhy' and 'Johnstone' tall fescue with low (< 1%) infestation rate o f Acremonium coenophialum from October 24 to December 19; 2) drylot fe eding of Johnstone and HE KY-31 haylage (December 19 to April 10); and 3) feedlot finishing on a common high-concentrate diet (April 11 to A ugust 1). In Phase 1, ADG was greatest (P < .05) for Kenhy, intermedia te for Johnstone and LE KY-31, and lowest (P < .05) for HE KY-31. Impl antation with estradiol 17-beta increased ADG (P < .01) by 23, 27, 7, and 2% for steers grazing Johnstone, HE KY-31, LE KY-31, and Kenhy, re spectively. Dry matter digestibility and DMI of stockpiled Johnstone a nd HE KY-31 were not different (P > .10). During Phase 2, steers consu ming Johnstone haylage had greater (P < .01) DMI, ADG, and gain:feed r atio (G:F) than steers consuming HE KY-31 haylage. During Phase 3, ste ers previously consuming Johnstone had greater DMI (P < .10); however, steers previously fed HE KY-31 had greater ADG (P < .05) and G:F (P < .01). By the end of the study, steer body weights were not different (P > .10) between treatments. These data indicate that growth-decreasi ng effects of endophyte-infested fescue were evident at hypothermal-am bient temperatures. Deleterious effects of consumption of endophyte-in fested fescue did not negatively affect subsequent feedlot performance .