Die Bodenkultur - Journal for Land Management, Food and Environment
L. GRUBER, G. WIEDNER, A. VOGEL and Th. GUGGENBERGER:
Nutrient and mineral content of forages in Austria Evaluation and interpretation of the forage analyses in the foodstuff laboratory at Rosenau of the agricultural board of Lower Austria
In the present investigation 7,556 forage analyses of the years 1989 to 1993 of the foodstuff laboratory at Rosenau of the agricultural board of Lower Austria have been evaluated. There are analyses of nearly all forages used in daily feeding practice. The standard forages of the winter period, however, are best represented by numbers up to 1,500. The usual methods were used in analysing the crude nutrients (tecator system), the minerals (atomic absorption spectralphotometry) and the in vitro-digestibility (Hohenheim gas production test). The energy evaluation was based on the digestibility coefficients of the DLG-tables (1991).
On an average the legumes show high crude fibre contents of partly more than 30 % and corresponding low energy concentration. The crude fibre contents of grass silage and hay of the first cut were on average 29 and 30 %, of the second cut 26 and 27 0/0, respectively. The results of maize silage (30 % DM, 23 % crude fibre, 6.4 MJ NEL) are satisfying. Of all types of forages regressions of protein and NEL content on crude fibre content have been computed, On the basis of these regressions the essential criteria for animal nutrition can be derived for the whole range of variation.
The legumes are characterized by high Ca-contents (6 to 15 g), the contents of P were, however, similar to those of the grasses. The forage of the meadows shows on an average the following values (6-10 g Ca, 2.6 to 3.7 g P, 21 to 26 g K).
The trace element contents of the grasses are a little higher than in the legumes.
The mineral content of silage maize is considerably lower than in the other forages (especially Ca and Mn). The relationships between crude fibre and mineral content are not uniform with respect to both the size and the sign, No general statement can therefore be given as to how and to what degree the mineral content changes depending on crude fibre content. The use of the individual linear regression equations, however, permits an estimate of the mineral content more exactly.
The determination of the energy concentration using the Hohenheim gas production test showed lower values than when deriving the energy concentration using the DLG-digestibility coefficients, especially in the range of lower energy concentration. In general both methods did not correspond well in the determination of the energy concentration (R2=42 %, n=608). Among the various types of forages the agreement between the two methods differed considerably. One possible explanation for these divergences could be that reduced digestibilities (e.g. by deficient conservation methods) are considered by in vitro-digestibility methods but not when using average data of foodstuff tables.
Key-words: Forage, crude nutrients, minerals, trace elements, in vitro-digestibility.