The use of Ca salts of rape seed fatty acids to protect protein against degradation in the rumen

The aim of this study was to evaluate the possibility of using Ca salts of rape seed fatty acids (CSRFA) as a means of protecting protein against degradation in the rumen. Four preparations were made, differing in their proportions of CSRFA and soyabean meal (SBM): 0:100, 50:50, 75:25 and 87.5:12.5 (on a DM basis). Protein degradability was estimated using the in sacco method with 8 and 16 h of incubation in the rumen of three bulls fed a diet consisting of a meadow hay and a concentrate mixture, given in the ratio 75:25 (% DM). The intestinal digestibility of the undegraded dietary nitrogen was determined using the mobile nylon bag technique with 16 h of preincubation in the rumen followed by soaking in pepsin-HCl solution. The protein solubility in vitro was estimated using protease from Streptomyces griseus. The standard procedure in sacco was also performed with the 0:100 and 50:50 mixtures, using four dry Simmental cows and 0, 2, 4, 8, 16, 24, 48 and 72 h of incubation in the rumen. decreased the DM and protein degradability of SBM in the rumen. After 16 h of incubation 0:818, 0:446, 0:282, 0:218 (P < 0.001) and 0.742, 0.329, 0.363, 0.230 (P < 0.001) of DM and protein were degraded for the 0:100, 50:50, 75:25 and 87:5,12:5 preparations, respectively. In vitro protein solubilities were 0.511, 0.187, 0.189 and 0.279 (P < 0.001). rease in the CSRFA:SBM ratio, particularly at 87.5,12.5, resulted in a decrease in total tract protein digestibility (TTPD; P < 0.001). However, except for the 87.5:12.5 mixture, there were no differences in the intestinal digestibility of rumen-undegraded dietary protein (IUPD), which was about 93%. ive protein degradabilities (for k = 0.06) were 0.630 and 0.342 for SBM and CSRFA:SBM (50,50), respectively. This significant effect arose from a great difference in the c values in the Ørskov and McDonald model (Ørskov and McDonald, 1979, The estimation of protein degradability in the rumen from incubation measurements weighted according to rate of passage, J. Agric. Sci. Camb., 92, 499–502).