Influence of feeding time as well as protein and energy intake on milk urea content

The influence of feeding before milking time was investigated in experiment 1. Cows were milked at the beginning, two hours or four hours after the be ginning of feeding (F0, F2, F4). Forage was fed ad libitum. Feeding before milking time did not significantly influence milk urea content (20.0, 20.2 and 21.5 mg/100 ml). In experiment 2 the influence of energy supply (90 % or 100 % of requiremen t, NEL90 or NEL100) and crude protein supply (140 % or 80 % of requirements , XP140 or XP80) respectively ruminal N-balance (+80 g or -80 g RNB), on mi lk urea content were tested. The experiment was conducted using 16 cows in a 4 x 4 Latin square design with four experimental groups (XP140NEL90, XP14 0NEL100, XP80NEL90, XP80NEL100). Crude protein concentration in groups XP80 was 8.8 % and 9.7 % and 16.3 % in groups XP140. Feed intake was significan tly higher in XP140 compared to XP80 (18.4 and 14.9 kg DM) and RNB was +80 and -89 g. RNB did not differ between NEL90 and NEL100. Milk yield (19,0 an d 20,0 kg ECM) as well as milk protein content (3.22 % and 3.29 %) increase d significantly with increasing energy supply. Milk urea content did not di ffer significantly between NEL90 and NEL100. Milk yield was increased by in creasing protein supply (17.6 kg or 21.8 kg ECM). Milk fat, protein and lac tose content as well as fat/protein-quotient were not affected by protein s upply. Differences in RNB between XP140 and XP80 led to significant differe nces in milk urea content (9.5 mg/100 ml and 36.8 mg/100 ml milk). As shown by regression analysis, a balanced RNB can be expected at a milk urea cont ent of 23 mg/100 ml. An increase of 10 g RNB enhanced milk urea content abo ut 1.7 mg/100 ml. The cow-individual standard deviation of milk urea conten t within an experimental period was about 3.6 mg/100 ml (2-8 mg/100 ml). Th is means a remarkably high coefficient of variation of 20.2 % (7-37 %).