Technical note: a modified three-step in vitro procedure to determine intestinal digestion of proteins

An in vitro, batch incubator (Daisy(II)) was used to simplify the 3-step, in vitro procedure (TSP) to reduce the cost and labor involved in the determination of intestinal digestion of proteins. Four tests were conducted to study the effects of the type of pepsin (P-7012 and P-7000; Sigma, St. Louis, MO), the type of bags used for the incubation of samples (R510 and F57; Ankom Technology, Fairport, NY), the amount of sample per bag (0.5, 1, 2, or 5 g), and the number of bags per incubation bottle (5, 15, 20, or 30 bags) on the estimated intestinal digestion of proteins. A soybean meal sample heated at 170 degrees C for 0, 0.5, 1, 2, 4, 6, or 8 h was used in all preliminary tests to determine the optimum conditions of the technique. The intestinal digestion of 12 protein supplements was determined using the Daisy(II) as well as the proposed TSP techniques. Results using the 2 types of pepsin were highly correlated: P-7012 = (0.99 +/- 0.04 x P-7000) -0.29 +/- 2.33 (r2 = 0.99, P < 0.001, n = 14). Intestinal digestion of soybean meal samples obtained from the TSP assay were highly correlated with those obtained using the Daisy(II) incubator with Ankom R510 bags: Daisy(R510) = (1.37 +/- 0.06 x TSP) -15.45 +/- 3.85 (r2 = 0.98, P < 0.001, n = 14); and Ankom F57 bags: Daisy(F57) = (1.33 +/- 0.06 x TSP) -15.76 +/- 3.87 (r2 = 0.98, P < 0.001, n = 14). Although there was a bias in these equations, when the whole protocol was applied to the determination of intestinal digestion of the 12 protein supplements using the TSP or the Daisy(II) technique with the Ankom R510 bags, the data were highly correlated: (0.93 +/- 0.12 x TSP) + 6.78 +/- 9.09 (r2 = 0.84, P < 0.001, n = 12). The amount of sample per bag and the number of bags per incubation bottle did not affect the estimates of intestinal digestion of proteins. These results indicate that the use of up to 30 nylon bags (Ankom R510) with 5 g of sample in each Daisy(II) incubation bottle could be used to estimate intestinal digestion of proteins in ruminants.