Evaluation of animal performance responses to the supplementation of 2 rumen-protected methionine supplements in post-peak-lactation Holstein cows

Abstract

Our objective was to evaluate the performance response of dairy cows fed a Met-deficient diet and provided a rumen-protected Met (RPM) supplement. A total of 24 multiparous (95 ± 20 DIM) and 6 primiparous (71 ± 3 DIM) Holstein cows were assigned to 1 of 3 treatments using a replicated 3 × 3 Latin square design with 21-d periods: a control diet deficient in MP Met by 17 g/d (CON) or the control diet plus 14 g/d of a RPM supplement, RPM-K or RPM-S, containing approximately 80% Met. Milk samples were collected on d 13 to 14 and 18 to 21 of each period. Plasma samples were collected on d 21 of each period. Contrasts were used to evaluate the effect of RPM addition (CON vs. RPM-K + RPM-S combined) and source of RPM (RPM-K vs. RPM-S). There was no difference between RPM-S and RPM-K in milk fat percentage (3.66 vs. 3.69%, respectively; P = 0.47) or milk protein percentage (3.28% for both treatments; P = 0.98), but RPM-K decreased DMI compared with RPM-S (26.2 vs. 26.6 kg/d; P = 0.02). Milk fat and protein percentages were increased by RPM relative to CON (3.60% fat and 3.25% protein; P = 0.02 and P = 0.04, respectively). Milk fat yield was not different between RPM-K and RPM-S (1.39 and 1.40 kg/d; P = 0.74), but milk fat yield tended to increase with RPM relative to CON (1.37 kg/d, P = 0.07). Plasma free Met was not different between RPM-S and RPM-K treatments (46.6 and 46.5 μ M , respectively; P = 0.97), and RPM supplementation increased plasma concentrations relative to CON (33.0 μ M ; P < 0.001). Relative to CON, both RPM supplements similarly increased milk fat, milk protein, and plasma free Met, suggesting similar relative bioavailability.