EFECTO DE DOS NIVELES DE PROTEÍNA CRUDA EN LA RESPUESTA PRODUCTIVA Y ECONÓMICA DE VACAS PARDO SUIZO

Abstract

Background. Dairy cows convert between 24 to 32% of dietary nitrogen (N) into milk protein, the rest of the dietary N is excreted in urine and feces that contributes to environmental N pollution. Besides the N excretions, dietary crude protein (DCP) represents up to 69% of the diet total cost. Therefore, the best was to reduce environmental pollution and to increase dairy profits is the reduction of crude protein in the diet of cows. Objective. To determine the effect of two dietary crude protein (DCP) levels 14 vs 16% on the productive and economic performance of Brown Swiss under confined management. Methodology. 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 dietary treatments 14 and 16% of DCP on a crossover design with two experimental period of three weeks each. Cows on experimental DCP 14% in period 1 switched to 16% in the second period, whereas cows that received a 16% diet in period 1 switched to 14% in period 2. Milk-to-feed price ratio and income over feeding cost were estimated as indicators of profitability. Results. 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% DCP had higher yields (0.57) than 14% DCP (0.55, kg/day). Cows in early and mid-lactation stage had higher performance than on late lactation (P < 0.05), on most of the response variables. Income over feeding costs were 0.24 and 0.21 ($ USD/kg) for DCP 14 and 16%, respectively. Total income over feeding cost per treatment was $1,020 for DCP 14%, and 917 for DCP 16%. Implications. The reduction of dietary crude protein in the diet of lactating cows will allow the reduction of N excretions to the environment and for farmers this strategy allows reductions in feeding cost. Conclusions. There were no differences in Brown Swiss cows performance to a reduction of DCP from 16 to 14%. Dietary crude protein treatment had lower milk production cost and generated higher incomes over feeding cost.