Effect of the content of vegetable crude protein in the diet on the utilization of urea in dairy cows. 1. Digestion of nitrogen and utilization of urea for bacterial protein synthesis in the rumen

Voigt, J.; Piatkowski, B.; Krawielitzki, R.; Sommer, A.; Ceresnakova, Z.; Engelmann, H.; Vancisin, J.; Girschewski, H.; Chrastinova, L.

Archiv für Tierernährung 33(4-5): 327-340


ISSN/ISBN: 0003-942X
Accession: 001190159

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The utilization of feed urea in the rumen was tested in 2 experiments with a total of 4 newly lactating dairy cows with rumen and duodenal re-entrant cannulae. With the energy supply constant in each case, the rations in experiment A contained 8.7, 12.4 and 14.6 and those of experiment B 10.7, 13.7 and 17.1% crude plant protein in DM. After supplementation with 120 and 150 g urea daily there were 11.9, 15.7 and 17.8 (A) and 13.8, 16.7 and 20.2 (B) % crude protein in DM. The rations consisted of maize silage and a pelleted mixture of straw and concentrates (A) or maize silage, lucerne hay and concentrates (B). They contained 10.3 to 10.6 (A) and 13.6 (B) kg DM with 5.6 to 6.0 (A) and 8.2 (B) kEFUcattle. With the increase of crude protein to between 16.7 and 17.8%, the absolute amount of non-NH3-N (NAN) in the duodenum increased as well. Between nitrogen intake (g/day, x) and NAN passage corrected by the amount of the endogenous quota (g/day, y) the relation y = 87.3 + 0.55x (r = 0.80) was established. NAN passage (y) as related to N intake decreased with the N concentration in the DM of the ration (x) according to the equation y = 0.35 + 1.22x-1 (r = 0.57). In experiment A 70, 62 and 61% and in B 55, 61 and 51% of the consumed amount of N were apparently absorbed in the intestines as NAN (without endogenous quota). The bacterial N yield of the rumen (g, y), estimated with diaminopimelic acid as microbial marker, was dependent on the consumed digestible organic matter (g, x) as follows: y = 67.3 + 0.021x (r = 0.69). There was no connection with the supply of N. The bacterial N yield showed that the utilization rate of the urea N decreased rapidly when there was more than 11 to 12% crude plant protein in the DM of the ration. For the tested ration type (570 to 600 EFUcattle/kg DM) the urea utilization potential in the rumen for crude plant protein concentrations of 8.7, 10.7, 12.4, 13.4, 13.7, 14.6 and 17.1% in the DM was 13.0, 6.9, 4.1, 2.6, 1.3 and -9.6 g urea per kg DM.