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Effect of strategic ration balancing with use of Prolak and USA-Lysine on the efficiency of milk protein production and environmental impact
The objective of this study was to evaluate the effect of a diet supplemented with a high quality protein and rumen protected lysine source on the efficiency of milk production and environmental impact in a commercial dairy herd. The general herd diet was reformulated with the Agricultural Model and Training System model and use of Prolak and USA-lysine. The control and treated diet had similar dietary CP concentration (17.7 % vs 17.6 %). Cows were completely randomized to two groups with 163 cows each pen and milked three times per day. The groups had similar average days in milk (135 vs 135) and parities (2.99 vs 2.84) prior to initiation of the trial. Respective diets were fed in a 40 d switch back design trial with two periods. Milk weight (all 3 milkings), and milk (sample from one of three milkings) and manure samples were obtained at the end of 2nd and 3rd weeks of each period for analysis. Cows fed the two diets had similar pen DMI (24.2 vs 24.1 kg/d), but the reformulated diet supported more milk yield (43.0 vs 44.9±0.15 kg/d), milk protein yield (1.27 vs 1.33±0.01 kg/d), milk fat yield (1.51 vs 1.57±0.01 kg/d), and increased ratio of milk true protein to total protein intake (29.4 vs 31.2%) and ratio of total milk protein to total protein intake (34.3 vs 36.5%).The concentration of MUN was higher when cows were fed reformulated diet (16.5 vs 18.7 mg/dl). Cows fed the reformulated diet consumed 2.6% less N, but produced 4.7% more milk N, and excreted 6.2% more predicted urinary N and 24% less calculated fecal N. Manure from cows fed the reformulated diet had lower ammonia (NH3) flux (145 vs 130 mg*h-1*m-2). This study illustrates that diets supplemented with high quality protein could improve efficiency of milk production and N utilization, and reduce the environmental impact.
Keywords: protected lysine, bypass protein, milk production