Nutritive value and energy content of the straw of selected Vicia L. taxa from Tunisia

The chemical composition and energy value of straws of Vicia sativa L. (varieties Languedoc and Mghila, and subspecies amphicarpa) and Vicia villosa Roth. (variety Sejenane and accession 2565) were investigated. The plants were grown in a Mediterranean environment, under identical environmental conditions. Total digestible nutrients (TDN) and energy values (digestible energy, metabolisable energy, and net energy for lactation) were estimated according to the equations developed by the 2001 Dairy National Research Council. Both ether extract (EE) or total fatty acids (FA) amounts, and digestible neutral detergent fibre (dNDF) calculated from chemical analysis or measured using a 48- hour rumen in vitro assay were used for calculations. Significant differences were observed in the chemical composition and energy value of the straws of the considered V. sativa and V. villosa varieties. Within the same variety, the TDN was similar using either EE or FA values for calculation. The energy resulted largely dependent on the dNDF values. Energy was higher when in vitro dNDF was used for calculation in low-NDF straw samples, while the opposite occurred for high-NDF samples.