Intake, Digestibility, and Nitrogen Balance of Steers Fed Gamagrass Baleage Topdressed at Two Rates of Nitrogen and Harvested at Sunset and Sunrise

Maximum diurnal accumulation of soluble carbohydrates in warm-season grasses is an economic way of increasing hay quality; however, in the humid East, haymaking is diffi cult. This study evaluated gamagrass (Tripsacum dactyloides L.), topdressed with either 56 (LO) or 168 (HI) kg N ha–1, direct baled after mowing in the afternoon (PM/LO and PM/HI) or morning (AM/LO and AM/HI), wrapped with plastic fi lm, and conserved as baleage. The four baleage treatments were evaluated by steers for dry matter intake (DMI), digestibility, and N retention. Neither harvest time nor N rate altered DMI (mean = 1.87 kg 100–1 kg body weight). Digestion was similar between PM and AM baleage but greater (P = 0.05) for HI vs. LO N rate (536 vs. 506 g kg–1) as was cellulose digestion (P = 0.02; 656 vs. 617 g kg–1). The digestion of crude protein was greater (P = 0.01) in the AM vs. PM baleage (519 vs. 443 g kg–1) and greater (P = 0.02) in HI vs. LO N rate (520 vs. 441 g kg–1). Fermentations differed (P < 0.01) between PM and AM baleage, as pH averaged 5.4 and 4.5, respectively. Greatest (P < 0.01) amounts of alcohols and least fatty acids occurred in PM baleage and N rate reduced (P < 0.01) alcohols but increased fatty acids. Total nonstructural carbohydrates (TNC) prebaling was 120 g kg–1 in the PM and 97 g kg–1 in the AM, but baleage averaged <38 g kg–1 and explains the lack of steer response to the PM harvest. Gamagrass preserved well as baleage and was readily consumed, but the TNC fraction was not preserved. A.K. Suavé, G.B. Huntington, and C.S. Whisnant, Dep. of Animal Science, North Carolina State Univ., Raleigh, NC 27695; J.C. Burns, USDA–ARS and Dep. of Crop Science and Dep. of Animal Science, North Carolina State Univ., Raleigh, NC 27695. Cooperative investigation of the USDA–ARS and the North Carolina ARS, Raleigh, NC 27695-7643. The use of trade names does not imply endorsements by USDA–ARS or by the North Carolina ARS of the products named or criticism of similar ones not mentioned. Received 27 Feb. 2009. *Corresponding author ( [email protected]). Abbreviations: ADF, acid detergent fi ber; AM, morning; BW, body weight; CELL, cellulose; CP, crude protein; DM, dry matter; DMD, dry matter digestion; DMI, dry matter intake; HEMI, hemicellulose; HI, N rate of 168 kg N ha–1; LO, N rate of 56 kg N ha–1; NDF, neutral detergent fi ber; NIRS, near-infrared refl ectance spectrophotometer; PM, evening; TNC, total nonstructural carbohydrates. Published in Crop Sci. 50:427–437 (2010). doi: 10.2135/cropsci2009.02.0105 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.