Distrubution de l'azote entre le lait, les fèces et l'urine chez la vache laitière alimentée aves des rations déficitaires en azote fermentescible

Abstract : The variation of the nitrogen distribution in the output compartments milk, urine and faeces has been studied in dairy cows. A model carried out by bibliographie analysis shows the central role of the crude protein leve! of diets on predictions of nitrogen recovery in milk or its losses in urine or faeces. All experimental diets are made using a systematically deficit of rumen fermentable nitrogen ( dPDI ~ 10 g/kg DM) to maximise utilisation in milk by favouring nitrogen recycling. The first trial confrrmed that ali N outputs increased with the CP level, running from 13 to 16% of the DM. The recovery rate in milk of nitrogen intake or digested nitrogen decreased whereas digestibility and relative urinary losses increased. A second trial showed for two CP levels (13% and 14%), that its determination on the nitrogen recovery in milk was independent of lactation state as this last factor and CP level affected separately milk nitrogen. The third trial studied the effect of an additional energy supply for two given CP levels in the diet (12% and 14%) on nitrogen outputs. This supply enhanced an increased nitrogen intake and apparent digestibility. No improvement by the supplementary energy of the recovery rate of fed nitrogen in milk has been noted for both CP levels. Even if urinary losses were similar between both energy supplies at both CP levels, at the higher level (14% CP) feed nitrogen loosed in urine as urea nitrogen is higher with the supplementary energy. In this case, the increased nitrogen intake are not completely buffered by a more efficient metabolic conversion into milk. For a given range of CP levels, the metabolic utilisation of feed nitrogen in milk in our trials was systematically higher than the bibliographie values in average. As recycling has been stimulated in all diets by a systematic deficit of fermentable nitrogen, this result could be du to an underestimated metabolic nitrogen supply. The nitrogen recovered in urine and faeces was Jess sensitively affected by this supplementary nitrogen source.
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Valérie Monteils. Distrubution de l'azote entre le lait, les fèces et l'urine chez la vache laitière alimentée aves des rations déficitaires en azote fermentescible. Sciences agricoles. Institut National Polytechnique de Lorraine, 2002. Français. ⟨NNT : 2002INPL100N⟩. ⟨tel-01749773⟩

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