PRODUCTIVE AND ECONOMIC PERFORMANCE OF BROWN SWISS COWS AT DIFFERENT STAGES OF LACTATION FED TWO CRUDE PROTEIN LEVELS

Abstract

<p><strong>Background. </strong>Dairy cows convert between 24 to 32% of dietary nitrogen (N<sub>2</sub>) into milk protein, the rest of the dietary N<sub>2</sub> is excreted in urine and feces which contributes to environmental N<sub>2</sub> pollution. Besides the N<sub>2</sub> excretions, crude protein (CP) represents up to 69% of the diet´s total cost. Therefore, the best way to reduce environmental pollution and increase dairy profits is the reduction of crude protein in the diet of cows. <strong>Objective. </strong>To determine the productive and economic performance of Brown Swiss cows at different stages of lactation fed two crude protein levels 14 vs 16%. <strong>Methodology. </strong>Twenty-three multiparous Brown Swiss cows stratified by stage of lactation as early (EL), mid (ML), and late (LL) were used and subjected to two CP levels 14 and 16% on a crossover design with two experimental periods (EP) of three weeks each. Cows on experimental CP 14% in the EP1 switched to 16% in the EP-2, whereas cows that received a 16% diet in the first EP switched to 14% in the EP2. Milk-to-feed price ratio and income over-feeding cost were estimated as indicators of profitability. <strong>Results. </strong>The were no significant differences in any response variable due to dietary crude protein (P > 0.05), except for milk protein yield (kg/day) (P = 0.03), where 16% CP had higher yields (0.57) than 14% CP (0.55, kg/day). Cows in early and mid-lactation stages had higher performance than in late lactation (P < 0.05), on most of the response variables. Income over feeding-costs were 0.24 and 0.21 ($ USD/kg) for CP 14 and 16%, respectively. Total income over feeding cost per treatment was $1,020 for CP 14%, and $917 for CP 16%. <strong>Implications.</strong> The reduction of crude protein in the diet of lactating cows will allow reductions if milk production cost, as well as reductions of N<sub>2</sub> excretions to the environment. <strong>Conclusions. </strong>The productive performance of the cows was not affected by a reduction of crude protein in the diet, but the reduction of crude protein resulted in lower milk production cost and higher income-over feeding cost.</p>