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

Abstract

Background. Dairy cows convert between 24 to 32% of dietary nitrogen (N2) into milk protein, the rest of the dietary N2 is excreted in urine and feces which contributes to environmental N2 pollution. Besides the N2 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. Objective. To determine the productive and economic performance of Brown Swiss cows at different stages of lactation fed two crude protein levels 14 vs 16%. 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 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. 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% 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%. Implications. The reduction of crude protein in the diet of lactating cows will allow reductions if milk production cost, as well as reductions of N2 excretions to the environment. Conclusions. 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.