Amino acid composition and nutritional value of italian ryegrass,red clover and lucerne as influenced by application and content of nitrogen

In experiments with increasing applications of nitrogen to ryegrass, red clover and lucerne grown in pots, freeze-dried plant material with widely varying N-content was obtained. Increasing N-concentrations were associated with increasing nitrate contents which proportionally decreased the concentrations (g/16 g total-N) of all amino acids. Expressed as g amino acid/16 g total-N minus NO₃-N, concentrations of all amino acids were closely similar at different N-levels. Differences between the three species ' amino acid composition were negligible except for a lower concentration of lysine in the crude protein of ryegrass and of methionine + cystine in the crude protein of clover and lucerne. In feeding experiments with rats increasing total-N concentrations were generally associated with higher true digestibilities of the crude protein of ryegrass, red clover and lucerne, but slightly lower biological values, especially in red clover. Net crude protein utilisation was increased by increasing total-N concentration in ryegrass, decreased in red clover and unchanged in lucerne. When ranked according to the nutritional value of the crude protein, ryegrass comes first, lucerne second and red clover last. Addition of synthetic methionine to ryegrass and lucerne improved their biological values by 30 and 47% respectively.