Effect of rotation frequency and weaning date on forage measurements and growth performance by cows and calves grazing endophyte-infected tall fescue pastures overseeded with crabgrass and legumes 1 K. P. Coffey* 2 , W. K. Coblentz*, D. A. Scarbrough 3 , J. B. Humphry 4 , B. C. McGinley 5 , J. E. Turner 6 , T. F. Smith†, D. S. Hubbell, III†, Z. B. Johnson*, D. H. Hellwig 7 , M. P. Popp‡, and C. F. Rosenkrans, Jr.* Departments of *Animal Science and ‡Agricultural Economics and Agri Business, University of Arkansas, Fayetteville 72701, and †Livestock and Forestry Branch Experiment Station, Batesville, AR 72501 ABSTRACT: A grazing study was initiated in April 2000 and continued through three calving and weaning cycles (ending July 2003) to investigate the effects of rotational grazing management (twice monthly [2M] vs. twice weekly [2W]) and weaning date (mid-April [EARLY] vs. early June [LATE]) on production of fall- calving cow-calf pairs (495 ± 9.6 kg initial BW) grazing Neotyphodium coenophialum-infected tall fescue (Fes- tuca arundinacea Schreb.) overseeded with legumes and crabgrass. Secondary objectives of the experiment were to monitor differences in quantity and quality of available forage and to evaluate changes in forage spe- cies composition. Pastures were dominated by tall fes- cue throughout the study, and the proportion of basal cover was greater (P < 0.05) in 2M than in 2W pastures. The percentage of legumes was very low across all treat- ment combinations, but the percentage of crabgrass continued to increase (P < 0.05) linearly and quadrati- cally across years for both summer and fall sampling periods, regardless of rotation or weaning program. In Key Words: Beef Cows, Fescue arundinacea, Forage, Legumes, Neotyphodium coenophialum, Tall Fescue 2005 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2005. 83:2684–2695 Introduction Cattle consuming Neotyphodium coenophialum-in- fected tall fescue (Festuca arundinacea Schreb.; E+) have 1 This project was funded in part by Grant # 2001-35209-10079 from the USDA National Research Initiatives Competitive Grants Agri-Systems Program. 2 Correspondence: B106E AFLS Bldg. (phone: 479-575-2112; fax: 479-575-7294; e-mail: kcoffey@uark.edu). 3 Former research specialist. Current address: 126 Jessie Dunn, Northwestern Oklahoma State University, Alva 73717. 4 Former research specialist. Current address: Humphry Environ- mental, Inc., Fayetteville, AR 72702. 5 Former graduate assistant. Current address: Stone Co. Extension Bldg., Mountain View, AR 72560. 2684 vitro DM disappearance and mineral concentrations varied minimally because of rotation frequency or weaning date. Rotation frequency did not substantially affect (P = 0.11 to 0.97) cow BW, hay offered, milk production, calving interval, calf birth weight, or actual or adjusted weaning weights; however, 2M cows had 0.3 units higher (P < 0.05) BCS at the time of breeding than 2W cows. Calves weaned late had greater (P < 0.05) actual weaning weight and weighed more (P < 0.05) on the LATE weaning date than on the EARLY weaning date, but 205-d adjusted weaning weights did not differ (P = 0.74) across weaning dates. Therefore, rotation frequency and/or weaning date had little effect on forage species composition or forage quality. In addi- tion, the rapid rotation program offered little advantage with respect to animal performance, and weaning fall- born calves grazing endophyte-infected tall fescue pas- tures at approximately 189 d of age seemed to be detri- mental to calf performance compared with delaying weaning until 243 d of age. exhibited decreased DMI (Goetsch et al., 1987; Forcherio et al., 1995; Humphry et al., 2002) and fiber digestion (Hannah et al., 1990; Humphry et al., 2002), lower cow and calf BW gains (Gay et al., 1988; Peters et al., 1992), and lower milk production (Ashley et al., 1987; Peters et al., 1992) compared with those consuming noninfected fescue. Weight differential between steers grazing E+ (288 g/kg of ergovaline) and those grazing fescue with a low infection (no detectable ergovaline) of N. coenophia- 6 Extension asst. prof. and extension specialist, Mountain Res. Stn., Dep. Anim. Sci., 239 Test Farm Rd., Waynesville, NC 28786. 7 Current address: Berea College, Berea, KY 40404. Received February 22, 2005. Accepted July 15, 2005.