Nitrogen excretions in dairy cows on a rotational grazing system: effects of fertilization type, days in the paddock and time period.

The present study aims to quantify nitrogen (N) excretions in dairy cows on a rotational grazing system with different types of fertilization (mineral N, slurry and compost) after 3 or 5 days in the paddock and during two different periods in June and September. Individual samples of faeces and urine were collected to assess N excretions from cows in the paddocks. The urea content in milk from the tank or from the individual cows was also measured. N intake was higher on day 3 compared to day 5 (465 vs 425 g d-1, P<0.001) and in September as compared to June (488 vs 425 g d-1, P<0.001) but was not influenced by the fertilization type. The amount of excreted urinary N was significantly higher in the mineral N group than in the two other groups (272 vs 226 g d-1; P<0.001). The N excretion in faeces and urines decreased with days (92 vs 84 g d-1, P<0.01; 256 vs 228 g d-1, P<0.001 respectively for days 3 and 5). Urinary N excretion was lower in June than in September (181 vs 302 g d-1, P<0.001) while the N excretion in the faeces was higher (96 vs 80 g d-1, P<0.01).