Influence of nitrogen fertilization on the nutritional value of high-lysine barley determined in growing pigs

An experiment was performed to examine the nutritional value of a high-lysine barley variety, Ca 7200202 (HLys) and four conventional barley varieties, namely cultivated varieties (cv) Galant, Inga, Romi and Zita, which were fertilized with either 0 or 180 kg nitrogen (N) ha−1. The barley varieties were used in N balance and digestibility studies in growing pigs. The lysine content of protein in cv HLys was 4.93 g/16 g N, at least 35.1% higher (p < 0.05) than the level of lysine in protein in the conventional varieties which ranged from 3.38 to 3.65 g/16 g N. In contrast, cv HLys had the lowest (p < 0.05) levels of glutamic acid and proline, 14.71 and 6.24 g/16 g N, respectively, which were at least 32.8% and 38.6%, respectively, lower than in the other barley varieties. N fertilization increased (p < 0.05) the protein (N × 6.25) level in the barley varieties from 95.0 to 147.0 g/kg dry matter (DM). The content (g/kg DM) of lysine, threonine and methionine in barley grain increased (p < 0.05) by 31.6%, 40.1% and 41.8%, respectively. Pigs fed the fertilized barley varieties retained more (p < 0.05) N and had a higher (p < 0.05) growth rate than pigs fed the unfertilized barley varieties. Pigs fed cv HLys retained the most (p < 0.05) N and cv HLys had the highest (p < 0.05) apparent biological value (BV, N retained/N digested). It is concluded that the development of high-lysine barley varieties is very beneficial for meeting the requirements of indispensable amino acids in pigs, and N excretion into the environment is substantially reduced due to a reduction in the prolamin (hordein) fraction which is rich in glutamic acid and proline. Furthermore, N fertilization greatly increases the nutritive value of barley by increasing the level of protein and therefore the concentration of indispensable amino acids.