Prediction of the energy content of tallgrass prairie hay

¹ Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506

^* To whom correspondence should be addressed. E-mail: kcolson{at}ksu.edu.

	Abstract

Experiments were conducted to describe the DE content of tallgrass prairie hay (TPH). In trial 1, steers (n = 13; 277 ± 15 kg) were used in a 13 x 4 Latin square experiment to measure DE of 13 samples of TPH fed at 1.5% of BW daily (average feeding level = 0.7 x the maintenance energy requirement). Hays were harvested from a variety of locations in east-central Kansas and represented an array of harvest dates and storage methods. In trial 2, steers (n = 16; 261 kg) were used in a randomized complete block to assess the effects of TPH intake level on DE. Hay was fed at 1.3, 1.7, 2.1 or 2.5% of BW daily, which corresponded to 0.9, 1.4, 1.6, and 1.9 x the maintenance energy requirement. Steers in both trials were fed soybean meal in amounts calculated to provide RDP equal to 11% of digestible OM intake. Hay samples were analyzed for ash, N, NDF, ADF, ADIN, neutral detergent-insoluble N, acid detergent-insoluble ash, lignin, monosaccharides, and alkali-labile phenolic acids. Chemical components related to DE (P < 0.2) were subject to iterative regression analysis to predict DE concentration of the diet. Iterations were ceased when the error mean square of the regression was optimized. At 0.7 x maintenance, dietary DE concentration (Mcal/kg) was described by DE = 0.13 [CP] - 0.16 [ADL] + 2.11 (R² = 0.73; S_y*x = 0.13). Forage OM digestion decreased linearly (P < 0.01) as forage intake increased. Apparent dietary DE concentration decreased 7.4% when intake was increased from 1x to 2x maintenance. When RDP was adequate, chemical composition values were useful indicators of forage DE content in our study. Moreover, increased forage intake depressed GE digestion by steers but ultimately increased total DE intake. Energy digestion varied with forage intake in a predictable manner between 1x and 2x the maintenance feeding level.

Key Words: chemical composition, digestible energy, forages, regression models