The increase of milk production at the farm level requires an accurate balancing of the diet and the nitrogensupply also to minimise the possible environmental pollution deriving from dairy farming. The aim of this studywas to evaluate dietary protein utilization at different crude protein (CP) levels and to predict nitrogen content infaeces on the basis of nutritional parameters and milk urea nitrogen content (MUN, mg dL-1). The study wasconducted on three groups (A, B, C) of lactating dairy cows (8 cows per group, including Latvian Brown andHolstein Black and White breeds) from 10 to 30 days in milk. Total mixed rations containing different levels of CP(approximately 18.0%, 17.5% and 17.0% for A, B and C, respectively) were fed. The amount of feed consumedby each cow was measured and feed samples collected during the trial. Milk yield (kg d-1) and faeces amountwere recorded, and samples were collected at day 21 of the study for further analysis. Feed samples wereanalysed for CP, net energy for lactation (NEL, MJ kg-1) and other parameters. Milk samples were analysed for fat(%), total protein (%), casein (%) and urea content (mg dL-1). The statistical investigation was conducted usingANOVA, and correlation and regression analyses. The results showed that milk yield, fat, total protein, casein,urea, and MUN were not significantly different among groups being not affected by the dietary CP levels. Thecorrelation between faecal nitrogen content and CP content in feed was moderately positive and statisticallysignificant (r=0.44, P=0.03), while the correlation between faecal nitrogen content and MUN was moderatelynegative and showed tendency towards significance (r=-0.39, P=0.06). The regression analysis showed that feedCP explained approximately 20% of faeces nitrogen content.
展开▼
