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

Abstract Text: A continuous-lactation experiment was conducted to evaluate the effect of dietary monensin supplementation and amino acid balancing (Lysine and Methionine) on milk yield, composition, component yields, and feed conversions (kg actual or component-corrected milk / kg DMI). Multiparous (n = 96) and primiparous (n =32) Holstein (n = 112) and Holstein × Jersey cross-bred (n = 16) cows were stratified by breed, parity, and DIM (104 ± 39 at trial initiation) 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 (CN; no monensin or amino acid balancing), amino acid balanced (AA), CN plus monensin (CNMN), or AA plus monensin (AAMN) for a 2-wk covariate period with cows fed a common non-experimental diet followed by a 10-wk treatment period with cows fed their assigned treatment diet. The TMR contained on average (DM basis) corn silage (37.5 %), alfalfa silage (23 %), and concentrate mixture (39.5 %). The AA and AAMN treatments were supplemented with blood meal and a ruminally-protected Methionine source (Ultramet®, Vita Plus Corp.; contains MetaSmart®, Adisseo) to achieve a 3:1 Lysine:Methionine ratio in the metabolizable protein. The MN and AAMN treatments were formulated using Rumensin® 90 (Elanco Animal Health) to provide a monensin intake of 540 mg/cow/d. Data were analyzed using Proc Mixed in SAS with covariate, monensin, amino acids, monensin x amino acids, week, and treatment x week interactions as Fixed effects and pen within treatment as a Random effect. DMI was reduced by monensin (26.6 vs 28.1 kg/d; P < 0.01). Milk yield was unaffected (P > 0.10) by treatment. Actual milk feed conversion was greater for cows fed monensin (1.82 vs. 1.73 kg milk/kg DMI; P = 0.03). Milk protein percentage and yield were increased by amino acids (3.16% vs. 3.09% [P < 0.01] and 1.53 vs. 1.50 kg/d [P = 0.03]), respectively. Component-corrected feed conversions were greater (P < 0.05) for cows fed diets containing monensin. Monensin × amino acid interactions were not (P> 0.10) detected for any of the parameters measured. Dietary monensin supplementation increased feed conversions, while milk protein percentage and yield were greater for cows fed the amino acid balanced diets.

Keywords: monensin, amino acids, dairy cows