Guanidination procedure increases standardised ileal digestibilities of nitrogen and amino acids in rapeseed meal, soybean meal and peas fed to growing pigs

A digestibility study was conducted to assess the effect of using the guanidination procedure to convert lysine to homoarginine in dietary sources of protein on standardised ileal digestibilities of nitrogen and amino acids in rapeseed meal, soybean meal or peas fed to growing pigs. Six barrows (German Landrace × Pietrain) with an initial bodyweight of 19 ± 1.8 kg, fitted with ileal T-cannulas, were fed one of three cornstarch-based diets that contained 180 g crude protein/kg (as-fed basis) from rapeseed meal, soybean meal or peas for an experimental period of 10 days according to a double 3 by 3 Latin square design. On Day 9 of each experimental period, the pigs were fed diets containing the guanidinated protein sources, which corresponded to their respective unguanidinated diets. In the guanidinated assay diets, 50% of the dietary source of protein was replaced, on an equal weight basis, with the guanidinated assay feed ingredient. Using the guanidination procedure increased the content of nitrogen in rapeseed meal, soybean meal, and peas by 17, 34, and 8 g/kg DM, respectively. With the exception of lysine in rapeseed meal, using the guanidination procedure increased the standardised ileal digestibilities of most amino acids in rapeseed meal, soybean meal and peas (P < 0.05). Lower standardised ileal digestibililty of lysine in guanidinated compared with unguanidinated rapeseed meal indicates that guanidination was not as uniform compared with the other sources of dietary protein. In conclusion, increases in standardised ileal digestibilities of amino acids after using the guanidination procedure in the aforementioned feed ingredients may be due to solubilisation of protein and degradation of antinutritional factors such as fibre, trypsin inhibitors and tannins. © 2013 CSIRO.