MILK PRODUCTION AND NITROGEN EXCRETION BY DAIRY COWS IN LATE LACTATION FED CUT PASTURES OF DIFFERENT RYEGRASS – CLOVER SPECIES IN SMALL-SCALE DAIRY SYSTEMS

Background: Nitrogen (N) plays an important role in dairy systems, both in production costs and as an indicator of environmental impact. Objective: The objective was to investigate the effects on milk production and nitrogen excretion by dairy cows fed cut pastures either of perennial ryegrass-red clover (PRG-RCL) or annual ryegrass-white clover (ARG-WCL), complemented with ground maize straw and of commercial concentrate. Methodology: Six dairy cows were used in a double cross-over on-farm experiment with 14-day experimental periods. Milk yield and composition, live weight, body condition score, chemical composition of feeds and N content in faeces, urine, milk and blood were recorded over the last four days of each experimental period. Results: No differences were found (P > 0.05) for milk yield nor composition. Cows on ARG-WCL had a higher N intake and N balance than those on PRG-RCL (P < 0.05); also, there were higher levels of blood urea nitrogen (BUN) and urine urea nitrogen (UUN) when cows were fed ARG-WCL than PRG-RCL (P < 0.05). Implications: This work allows us to know the amount of nitrogen excreted in milk production in small-scale dairy systems. Conclusions: It is concluded that PRG-RCL may be a feeding strategy to reduce N excretion and achieve higher efficiency in N use for small-scale dairy systems.