Effects of selected endophyte and tall fescue cultivar combinations on steer grazing performance, indicators of fescue toxicosis, feedlot performance, and carcass traits1–3

• Published in: Journal of animal science 2013-01, Vol.91 (1), p.342-355
• Main Authors: Parish, J. A., Parish, J. R., Best, T. F., Boland, H. T., Young, C. A.
• Format: Article
• Language: English
• Subjects: Animal diseases; Animal sciences; Cattle; Feeds; Grasses; Meat
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2011-4725

Five tall fescue [Lolium arundinaceum (Schreb.)] pastures [wild-type 'Kentucky-31' with 78.0% of plants infected with ergot alkaloid-producing endophyte Neotyphodium coenophialum (KY31 E+), 'Jesup' AR542 endophyte-infected contaminated with 30.3% tall fescue containing ergot alkaloid producingendophyte (Jesup AR542 E+); 'GA-186' AR584 endophyte- infected contaminated with 11.8% tall fescue containing ergot alkaloid producing-endophyte (AGRFA 140); 'PDF' AR584 endophyte-infected contaminated with 5.5% tall fescue containing ergot alkaloid producing-endophyte (AGRFA 144); and 'KYFA 9301' AR584 endophyte-infected contaminated with 10.0% tall fescue containing ergot alkaloid producing-endophyte (AGRFA 150)] were compared for steer growth performance, toxicity, feedlot performance, and carcass traits. Steers (mean initial BW = 322 kg) grazed pastures for 84 d in spring and 56 d in autumn for 2 yr. Steers were shipped after grazing in Prairie, MS, to Macedonia, IA, for finishing. Mean herbage mass was not different (P = 0.15) among pastures. Posttreatment (d 28+) serum prolactin concentrations were depressed (P = 0.013) on KY31 E+. Steers grazing KY31 E+ had greater (P < 0.01) posttreatment rectal temperatures during spring. Spring hair coat scores were greatest (P < 0.01) on KY31 E+ at d 56 and 84. Steer ADG was least (P < 0.01) on KY31 E+ in spring and depressed (P = 0.014) on KY31 E+ and Jesup AR542 E+ in autumn. Spring grazing ADG was greater (P = 0.049) on AGRFA 150 than Jesup AR542 E+ and AGRFA 140. No BW differences (P = 0.09) among pastures were seen at reimplant during feedlot finishing. Pasture had no effect on ADG after reimplant (P = 0.68), days on feed (P = 0.56), or fi nal BW (P = 0.55). Exposure to fescue toxicosis did not affect (P ≥ 0.19) carcass traits. Hair coat price discounts applied for spring-grazed steers on KY-31 E+ affected (P < 0.01) initial steer monetary values. There were no pasture differences for finishing costs (P ≥ 0.61) or final carcass value (P = 0.59). Elite tall fescue cultivar and novel endophyte combinations improve growth performance of grazing calves over KY31 E+. Producers whose calves graze KY-31 E+ tall fescue should consider retaining ownership of these cattle through feedlot finishing to avoid market discounts and capture value from compensatory BW gains during finishing. [PUBLICATION ABSTRACT]