Nutrition of dairy cows in summer and nitrogen excretion.

Nutrition and production of 200 Friesian cows, which produced 24 kg milk a day, were monitored during five summer months. In September, the amount of total non-protein and ammonia nitrogen were determined in faeces, which were taken from ten cows' recta, and in slurry. A model of regression equations, which were introduced by Kirschgessner et al. (1993), was used to estimate daily amount of excreted nitrogen depending on few parameters. Cows excreted on average 301 g nitrogen a day depending on average consumed dry matter, depending on average consumed nitrogen 341 g, and depending on daily amount of milk 271 g. Faeces contained 34.04 ± 1.69 g total, 6.36 ± 0.76 g non-protein and 2.07 ± 0.33 g ammonia nitrogen, slurry contained 96.77 g total, 72.22 g non-protein and 57.15 g ammonia nitrogen, all per kg of dry matter. Protein surpluses in a ration reflected in more excreted nitrogen by urine while only in traces by faeces.