The chemical composition and nutritive value for ruminants of four possible energy crops and their residues of anaerobic fermentation

Abstract

The chemical composition and potential nutritive value for ruminants of fresh energy crops, Jerusalem artichoke cv. Topianca ( Helianthus tuberosus L.) and cv. No. 1168 ( Helianthus tuberosus × annuus), lucerne ( Medicago sativa L.) and Garden orach ( Atriplex hortensis L.), and their residues after they were subjected to anaerobic fermentation were studied. The nitrogen content and the proportion of nitrogen in the acid-detergent fibre fraction was greater in the residues after fermentation. The solubility of nitrogen in buffer and in acid-pepsin was less in all crops after fermentation while only minor changes were seen in the amino-acid profiles. The rumen degradability of nitrogen was greater after biogas fermentation of lucerne and Garden orach, but less with Jerusalem artichoke (Topianca and No. 1168). The contents of extractable and fibrous carbohydrates were higher in Jerusalem artichoke (Topianca and No. 1168) and Garden orach than in lucerne. The uronic acid content was highest in lucerne. The rumen degradability of organic matter and of fibre (neutral-detergent fibre) was lower in fresh Jerusalem artichoke (Topianca and No. 1168) and Garden orach than in fresh lucerne and was markedly reduced in all crops after biogas fermentation. Decreasing rumen degradability of organic matter was negatively correlated ( r = −0.94) and the increasing proportion of rumen undegradable neutral-detergent fibre was positively correlated ( r = 0.88) with the increase of lignin in the dry matter. Due to the low digestibility of organic matter (energy content) and the high nitrogen content, the residues after biogas production have a potential primarily as nitrogen supplements to diets low in nitrogen.