The nutritive value for ruminants of lupin seeds from determinate and dwarf determinate plants

Lupin seeds produced from new varieties of determinate (Lucyane) and dwarf determinate (Lunivers) the UK-grown, autumn-sown genotypes were studied for their chemical composition including fatty and amino acid contents together with the rumen degradation of nitrogen (N) and the post-ruminal availability of undegraded N. The effect of sample preparation on N solubility was also examined and SDS–PAGE was used to characterise the molecular mass of proteins present in the seeds. The composition of the lupin seeds were broadly similar although variety Lunivers had a higher crude protein content than the other samples (368 g kg−1 dry matter (DM) compared with a mean of 326 g kg−1 DM for the others) and this was all accounted for as amino acids. The amino acid profile of all samples were similar. Rumen degradable N ranged from 580 to 690 g kg−1 total N, water soluble N was lowest in Lunivers and this was associated with many more individual protein-related bands with molecular masses in excess of 40 kDa than the non-dwarf determinates. The N solubility increased with declining mill screen size from 8 to 1 mm following which it did not change. The new varieties of determinate lupin have considerable potential as a protein source for productive ruminants in the UK and in particular the dwarf determinate type (Lunivers) appears particularly promising. In addition, sample preparation can have a large impact on the measured N solubility and degradability and standardisation is needed to enable worthwhile comparisons with other protein sources to be made.