Evaluation of the homoarginine technique for measuring true ileal amino acid digestibilities in pigs fed a barley-canola meal-based diet

Abstract

The homoarginine technique has been suggested as a means to determine true ileal amino acid digestibilities in nonruminant animals fed protein-containing diets. Conditions for guanidinating lysine to homoarginine in barley and canola meal and the effect of this process on nutrient composition and ileal digestibilities in the resulting material were investigated. Conditions tested were methylisourea concentration (0.4, 0.5, or 0.6 M) and reaction time (4 or 6 d) at pH 10.5. Using 0.4 methylisourea M solution for 4 or 6 d gave guanidination rates of 72.5 and 78.5% for barley and 72.3 and 75.2% for canola meal, respectively. Using 0.5 M gave 88.0 and 84.6% guanidination rates in barley and canola meal, respectively, after a 6-d reaction time. Under these conditions, guanidination did not change the nutrient composition of barley (P > 0.10), whereas it increased CP (38.4 vs 49.0%), crude fiber (10.2 vs 16.0%), acid detergent fiber (30.0 vs 43.4%) and neutral detergent fiber (29.8 vs 49.4%) levels in canola meal (P < 0.05). Four 33.6-kg barrows fitted with a simple T-cannula at the terminal ileum were fed a 16% CP unguanidinated barley and canola meal-based diet for four consecutive 14-d periods. Ileal digesta were collected continuously for 24 h on d 12 and 14 to determine apparent nutrient digestibilities. On the morning of d 14, pigs were fed a diet in which half of the barley and canola meal was replaced with guanidinated material for determining true ileal amino acid digestibilities. Digesta samples were pooled by pig and by 24-h period to give 16 observations per diet. Apparent ileal digestibilities of DM, CP, and AA in the unguanidinated and guanidinated barley-canola meal diet were similar (P > 0.10) despite the changes observed in canola meal. Apparent ileal lysine digestibility was 73.9 and 74.5% in the unguanidinated and guanidinated diet, respectively. The true ileal lysine digestibility was 88.1%. The present results show that guanidination does not interfere with digestion and further support the use of the homoarginine method for determining true ileal amino acid digestibilities in pigs fed practical diets. A methylisourea solution of 0.5 M and a 6-d reaction time are recommended for converting lysine to homoarginine in barley and canola meal.

Apparent ileal amino acid digestibility and energy utilization in hulless oats (<i>Avena nuda</i> L) fed to growing pigs

“…Pigs were individually housed in adjustable metabolism crates (1.8 x 0.6 m) with smooth transparent plastic sides and plastic-covered expanded metal sheet flooring in a temperature-controlled room (22 ± 2°C). Pigs were allowed to adjust to the metabolism crates for 8 d before they were surgically fitted with a T-cannula at the distal ileum and cared for as described by Nyachoti et al (2002).…”

Energy and nutrient digestibility in a hulless low-phytate phosphorus barley fed to finishing pigs

“…Six Genesus (Yorkshire-Landrace dam )Duroc sire) barrows with an initial BW of 5995 kg and fitted with a T-cannula at the terminal ileum, as described by Nyachoti et al (2002), were used in this study. Pigs were housed individually in pens with raised, plastic-covered, woven metal floors and smooth walls (1.45 m)1.13 m) in a temperature-controlled room (22928C).…”

Use of the guanidination reaction for determining reactive lysine, bioavailable lysine and gut endogenous lysine

“…bran layer and hulls seeds) where grinding to a very small particle size may not always be possible. Consequently, the assumption that true ileal homoarginine digestibility is equivalent to true ileal lysine digestibility is pivotal, particularly if the extent of guanidination is low, or for studies where guanidinated protein sources are diluted with their undiluted counterparts prior to testing (Nyachoti et al 2002). Several studies have been conducted, however, that have compared the in vitro digestion and apparent and true ileal amino acid digestibility of unguanidinated and guanidinated dietary protein sources (Caine et al 2008;Eklund et al 2013;Nyachoti et al 2002;Schmitz et al 1991).…”

“…One example may be the removal of anti-nutritional factors during the washing step (used to remove unreacted OMIU) which may in turn lead to a reduction in the amount of endogenous losses (Eklund et al 2013). If guanidination of the diet is not complete, then any residual undigested dietary lysine present in ileal digesta can be corrected based on the digestibility of homoarginine present in the diet (Marty et al 1994;Moughan and Rutherfurd 1990;Nyachoti et al 2002), where it is assumed that the true ileal homoarginine digestibility is equivalent to the true ileal lysine digestibility. However, in this case homoarginine does need to be determined in the digesta.…”