In situ rumen degradability and in vitro intestinal digestibility of rumen-protected methyl donors and lysine


Rumen degradation and intestinal digestibility of rumen-protected (RP) methyl donor and lysine products vary. Our objectives were to evaluate the in situ rumen degradability and in vitro intestinal digestibility of 4 RP products containing choline chloride, dl-methionine, betaine, and/or l-lysine in a triglyceride matrix. Four rumen-cannulated multiparous Holstein cows (175 ± 4 DIM; 34 ± 6 kg of milk/d) were used to test commercially microencapsulate products (Vetagro S.p.A., Reggio Emilia, Italy) which contain 25% choline chloride (RPC; Ruprocol), 55% dl-methionine (RPM; Timet), 33% l-lysine (RPL; ReLys) and 22% methionine, 10% choline chloride, 3% betaine, < 1% riboflavin and vitamin B12 (RPMD; MecoVit). The difference in composition was composed of hydrogenated palm fat. In paired duplicates, 5 g of RP product were placed in separate nylon bags and rumen-incubated for 0, 4, 8, 16, and 20 h. Bags were inserted in reverse order, removed collectively after incubation and washed in cold tap water. Intestinal digestibility was in vitro estimated using 16 h samples and an enzyme cocktail containing lipase (28 U/mL). All in situ and in vitro samples were dried and composited for N analysis using block digestion and steam distillation with automatic titration. The statistical model included the random effect of cow and replicates, and the fixed effects of product, time and their interaction. The percentage of N that passed the rumen varied across product (P < 0.001) and time (P < 0.001), and interactions were detected (P < 0.05). Percentage of rumen-undegraded N following in situ incubation is shown in Table 1. In vitro intestinal digestibility was 54.8 ± 3.48%, 78.1 ± 3.26%, 64.6% ± 2.89, and 74.9 ± 3.41% for RPC, RPM, RPL and RMD, respectively. Rumen protection for RPM, RPL, and RPMD was high, relative to RPC. Intestinal digestibility was high for all products tested. Table 1 (Abstr. T180). Least squares means of rumen-undegraded nitrogen following in situ incubation

Product Undegraded N, % SEM
4 h 8 h 16 h 20 h
RPC 68.8 54.3 40.2 31.5 2.33
RPM 91.2 81.1 74.3 70.4 3.17
RPL 89.4 85.6 75.6 68.9 2.33
RPMD 76.2 64.8 51.7 49.1 3.13

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