The nutritional value of high-lysine barley determined in rats, young pigs and growing pigs

Three experiments, the first with rats, the second with young pigs and the third with growing pigs, were carried out to compare the nutritional value of cv Lysimax, a newly developed high-lysine barley, to cv Lami, a conventional barley grown in Denmark. In the diets for rats and growing pigs the barleys were the sole protein source while in the experiment with young pigs the barleys made up to 649 g kg-1 of the respective diets. The lysine content of cv Lysimax was 52.6% higher than that of cv Lami; 4.99 g 16 g N-1 compared to 3.27 g 16 g N-1. The contents of threonine, tryptophane, methionine and cystine of cv Lysimax were 3.80, 1.41, 1.80 and 2.27 g 16 g N-1, respectively; being 18.4, 8.5, 9.8 and 5.1% higher than in cv Lami. Conversely, the contents of glutamic acid and proline in cv Lysimax were 15.79 and 7.40 g 16 g N-1, respectively, being 36.1 and 40.0% lower than in cv Lami. In the experiment with rats, the higher lysine content and the lower content of glutamic acid and proline in cv Lysimax resulted in a 34.8% increase (P < 0.05) in biological value (BV); 0.867 for cv Lysimax compared to 0.643 for cv Lami. True protein digestibilities and energy digestibilities in rats fed cv Lysimax were 0.019 and 0.010 units lower (P < 0.05) than for cv Lami. For young pigs the increased lysine content and the lower content of glutamic acid and proline of cv Lysimax increased (P < 0.05) nitrogen (N) retention from 10.9 to 12.4 g day-1, respectively, and increased (P < 0.05) apparent BV from 0.690 to 0.734, respectively. The digestibility of energy was 0.030 units lower (P < 0.05) for the diets with cv Lysimax than for the diets with cv Lami. Likewise, with growing pigs the increased lysine content and the lower content of glutamic acid and proline increased (P < 0.05) N retention from 6.4 to 10.8 g day-1 and apparent BV from 0.271 to 0.495, respectively. The apparent ileal digestibilities of lysine, threonine, tryptophane, methionine and cystine were similar (P > 0.05) between the barleys. It is concluded that the development of high-lysine barley varieties could be beneficial for meeting the requirements of essential amino acids for monogastrics. Moreover, N excretion into the environment was substantially reduced due a reduction in the prolamine fraction which is rich in glutamic acid and proline.