Apparent synthesis of thiamin and vitamin B12 in rumen of lactating dairy cows fed alfalfa or orchardgrass silages of different particle lengths

Abstract Text:

Effects of forage particle length on apparent ruminal synthesis and post-ruminal supply of thiamin and vitamin B₁₂ were evaluated in two experiments. Alfalfa and orchardgrass were harvested and ensiled at two theoretical lengths of cut: 19-mm (long cut, LC) or 10-mm (short cut, SC).  Within a forage type, rations containing silages of each length of cut as the sole forage were offered to ruminally and duodenally cannulated lactating Holstein cows in crossover design experiments. Experiment 1 compared diets containing LC and SC alfalfa silage (~47% forage, ~20% forage NDF and ~25% total NDF) offered to 13 cows in two 19-d treatment periods.  Experiment 2 compared diets containing LC and SC orchardgrass silage (~50% forage, ~23% forage NDF and ~28% total NDF) offered to 15 cows in two 18-d treatment periods.  In Experiment 1, intakes of thiamin and vitamin B₁₂ were greater (P<0.01) for LC than SC (thiamin: 89.4 vs. 77.5 ± 2.13 mg/d; vitamin B₁₂: 118.6 vs. 67.1 ± 2.55 µg/d). Neither duodenal flows of thiamin (P=0.94, 174.2 ± 18.87 mg/d) and vitamin B₁₂ (P=0.17, 8223 ± 713.0 µg/d) nor apparent ruminal synthesis of these vitamins (thiamin, P=0.15, 90.9 ± 17.82 mg/d; vitamin B₁₂, P=0.16, 8131 ± 711.0 µg/d) were affected by treatment in Experiment 1. In Experiment 2, there was no effect of treatment on the intake of vitamins (thiamin, P=0.79, 71.9 ± 2.55 mg/d; vitamin B₁₂, P=0.85, 111 ± 3.9 µg/d), duodenal flows (thiamin, P=0.80, 156 ± 9.5 mg/d; vitamin B₁₂, P=0.88, 6887 ± 476.0 µg/d), or their apparent ruminal synthesis (thiamin, P=0.82, 84.1 ± 8.14 mg/d; vitamin B₁₂, P=0.88, 6725± 473.0 µg/d). The reduction of legume particle length decreased the dietary supply of thiamin and vitamin B₁₂. However, forage particle length, in the studied range, did not affect apparent synthesis of thiamin and vitamin B₁₂ in rumen or the supply of these vitamins to the sites of absorption.  

Keywords: dairy cow, thiamin, vitamin B₁₂