Estimation of energy value of grassland forage.

Concentration of metabolizable energy (ME) and net energy for lactation (NEL) of 19 samples of green forage, 5 samples of grass silage and one sample of hay with known in vivo measured digestibility were estimated according to official German system (DLG, 1997). Energy value and organic matter digestibility (dOM) were comparatively estimated on the basis of chemical composition and digestibilities from tables. It was established that on the basis of data form DLG tables dOM was underestimated for 2.1 ± 3.95%, concentration of ME for 0.29 ± 0.52 MJ and concentration of NEL for 0.21 ± 0.37 MJ kg dry matter (DM). Somewhat lower deviation from in vivo estimates were obtained in estimation of ME (0.04 ± 0.45 MJ kg DM) and NEL (0.03 ± 0.33 MJ kg DM) on the basis of chemical composition and regression equations from literature (GfE, 1998). By the use of Hohenheim gas production test (in vitro) and adequate regression equations from literature the accuracy of estimate was increased markedly. Relatively precise was found to be the equation by (Menke and Steingass, 1987), which in comparison to in vivo estimation underestimated the concentration of ME for 0.12 ± 0.26 MJ and concentration of NEL for 0.09 ± 0.19 MJ kg DM. Equations by Aiple et al. (1995) overestimated in vivo estimated concentration of ME for 0.15 ± 0.24 MJ kg DM and concentration of NEL for 0.10 ± 0.17 MJ Babnik, D. in Verbic, J. Ocenjevanje energijske vrednosti krme s travinja. Zb. Biotehniške fak. Univ. v Ljubljani. Kmetijstvo. Zootehnika, 76(2000)2 62 kg DM. The major part of variability in concentration of ME can be explained with multiple regression equation on the basis of gas production, which is developed during the incubation of samples with rumen liquor and concentration of crude fat (R = 0.96).