Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/1/2005
Publication Date: 11/1/2005
Citation: Coffey, K. P., W. K. Coblentz, D. A. Scarbrough, J. B. Humphry, B. C. McGinley, J. E. Turner, T. F. Smith, D. S. Hubbell, III, Z. B. Johnson, D. H. Hellwig, M. P. Popp, and C. F. Rosenkrans, Jr. 2005. Impact of rotation frequency and weaning date on forage availability and nutrient composition, species composition, and growth performance by cows and calves grazing endophyte-infected tall fescue pastures overseeded with crabgrass, lespedeza, and red and white clover. Journal of Animal Science. 83:2684-2695. Interpretive Summary: Producers interested in reaping quick returns from additional fencing costs incurred with intensive rotational grazing might be discouraged from investing in extra fencing if they wish to wean fall-born calves early. Weaning late led to greater calf weights and might be the preferred method for producers selling their calves at weaning in the cash market, especially because grazing of additional forage using extra cows was not a viable management option under the conditions encountered in this study. Therefore, it is likely that if improvements in beneficial plant species, carrying capacity, and forage quality resulting from weaning date or more frequent pasture rotation are to be realized, they will require more than 3 yr to become evident on sites such as the one used in the present study that have steep slopes and poor soil characteristics.
Technical 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 (Festuca 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 species composition. Pastures were dominated by tall fescue 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 treatment combinations, but the percentage of crabgrass continued to increase (P < 0.05) linearly and quadratically across years for both summer and fall sampling periods, regardless of rotation or weaning program. In 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 addition, the rapid rotation program offered little advantage with respect to animal performance, and weaning fall-born calves grazing endophyte-infected tall fescue pastures at approximately 189 d of age seemed to be detrimental to calf performance compared with delaying weaning until 243 d of age.