Effect of dietary monensin supplementation and amino acid balancing on lactation performance by dairy cows

Abstract

A replicated-pen experiment was conducted to determine effects of dietary monensin supplementation and amino acid balancing on lactation performance by dairy cows. Cows (n = 128) were stratified by breed, parity, and DIM and randomly assigned to 16 pens of 8 cows each. Pens were randomly assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement of treatments: control (no monensin or amino acid balancing), amino acid balanced (AA), control plus monensin (CNMN), or AA plus monensin (AAMN) for a 2-wk covariate period followed by a 10-wk treatment period. The TMR contained, on average (DM basis), corn silage (37.5%), alfalfa silage (23.0%), and concentrate mixture (39.5%). The AA and AAMN treatments were supplemented with blood meal and ruminally protected methionine to achieve a 3:1 lysine:methionine ratio in the metabolizable protein. The CNMN and AAMN treatments were formulated to provide a monensin intake of 540 mg/d per cow. Data were analyzed with pen as the experimental unit. Dry matter intake was reduced (P < 0.01) by monensin supplementation (26.9 vs. 27.6 kg/d per cow). Feed conversion was greater (P = 0.03) for cows fed monensin (1.81 vs. 1.75 kg of milk/kg of DMI). Milk protein percentage and yield were increased (P < 0.01 and P = 0.03, respectively) by amino acid balancing (3.15 vs. 3.08% and 1.53 vs. 1.49 kg/d per cow, respectively). Component-corrected feed-conversion ratios were greater (P = 0.02) for cows fed monensin. Dietary monensin supplementation increased feed-conversion ratios through reduced DMI, and milk protein percentage and yield were greater for cows fed the amino acid–balanced diets.