Apparent synthesis of thiamin, riboflavin, vitamin B6 and vitamin B12 in rumen of lactating dairy cows fed 2 concentrations of nitrogen and 2 energy sources

Abstract Text: Effects of nitrogen supply and energy sources on apparent ruminal synthesis (ARS) and post-ruminal supply of thiamin, riboflavin, vitamin B₆, and vitamin B₁₂ were evaluated using 4 lactating Holstein cows distributed in a 4×4 Latin square design with treatments arranged according to a 2×2 factorial. The cows were fitted with cannulas in proximal duodenum. The treatments were 2 concentrations of nitrogen: HIGH: 14% CP, i.e. 110% of the protein requirements and an adequate supply in rumen-degradable protein (RDP), vs. LOW: 11% CP, i.e. 80% of the protein requirements with a shortage in RDP; energy sources were STARCH from barley, corn, and wheat vs. FIBER from soybean hulls and dehydrated beet pulp. Diets were corn silage based, had the same forage: concentrate ratio (60:40, dry matter basis) and were isoenergetic. STARCH resulted in greater (P<0.01) intakes of thiamin (51 vs. 34 ± 2.4 mg/d), riboflavin (1172 vs. 1050 ± 25.8 mg/d) and vitamin B₆ (202 vs. 161 ± 3.9 mg/d) as compared with FIBER, whereas nitrogen concentrations had no effect (P≥0.76). Vitamin B₁₂ intake was not affected by treatments (P≥0.43) and averaged 86 ± 2.0 µg/d. Duodenal flow (P=0.34; 35 ± 7.0 mg/d) or ARS (P=0.46; -6 ± 7.6 mg/d) of thiamin were not significantly affected by treatments. STARCH increased duodenal flow of riboflavin (P<0.01; 1546 vs. 1091 ± 92.4 mg/d) and vitamin B₆ (P<0.01; 68 vs. 45 ± 4.9 mg/d) but decreased vitamin B₁₂ flow (P<0.01; 3127 vs. 9319 ± 731.1 µg/d) as compared with FIBER. HIGH nitrogen increased riboflavin and vitamin B₆ duodenal flows (P=0.02; 1481 vs. 1156 ± 85.5 mg/d and P=0.01; 67 vs. 47 ± 4.6 mg/d, respectively) and ARS (P=0.04; 372 vs. 43 ± 95.2 mg/d and P=0.04; -114 vs. -135 ± 6.3 mg/d, respectively). Nitrogen supply had no effect on vitamin B₁₂ duodenal flows (P=0.64) or the ARS (P=0.63). Energy sources had no effect on ARS of vitamin B₆ (P=0.11) but STARCH tended to increase the apparent production of riboflavin (P=0.06; 374 vs. 41 ± 102.3 mg/d). Inversely, FIBER enhanced ARS of vitamin B₁₂ (P<0.01; 9234 vs. 3040 ± 730.3 µg/d, respectively). There was no interaction between treatments (P≥0.09). The apparent ruminal balance was affected by the nitrogen concentration for synthesis of riboflavin and degradation of vitamin B₆, and by the energy sources for synthesis of riboflavin and vitamin B₁₂.

Keywords: apparent ruminal synthesis, B vitamins, dairy cow