Influence of dietary protein on urea levels in blood and milk of buffalo cows

The aim of the study described herein, was to verify the influence of changing protein levels in buffalo cow diets on quantity-quality of milk yield, blood (BU) and milk (MU) urea, metabolic profile and milk freezing point (MFP). The experiment was carried out on eight buffaloes divided into two trials (trial 1 and trial 2), each trial divided into tree periods (P1, P2 and P3). The levels of CP/DM in the three periods were 9%, 12% and 9%, respectively. Buffaloes of trials 1 and 2 were different for days in milk (DIM = 164 vs. 132, respectively) and for milk yield (7 kg vs. 10 kg, respectively). Protein requirements were consistently met in trial 1 buffaloes, while the subjects of trial 2 were protein deficient in periods P1 and P3. The increase of CP/DM (P2) increased milk protein level and quantity, and MU in trial 2. The CP/DM increase caused, moreover, a decrease, and therefore an improvement in the MFP, and an increase in BU values in both trials. Multiple regression analyses showed a strong link between MU and BU (R-2 = 0.769; P < 0.01) and between MU and BU as regards protein/energy ratio. The MFP, moreover, varied according to MU values (R-2 = 0.685; P < 0.01). The increase in protein concentration in subjects whose protein requirements had already been met, (trial 1) brought about an excess of protein which probably triggered a more intense gluconeogenesis confirmed by the higher glycemia levels (P < 0.01) in P2. In trial 2, on the other hand, the protein requirements met in P2 resulted in greater milk yield, which, not being backed up by the energy levels in the diet, caused a relative energy deficiency in the animals. This hypothesis is confirmed by the increase in beta-hydroxybutyrate and lipoproteins as well as the lower body condition score levels in P2 vs. P1 and P3. The existing connection between protein/energy ratio and MU could indicate that in buffalo, as in cattle, MU can be used as a valid parameter in order to highlight the existence of an alteration in the protein/energy ratio of the diet. The normalization of the MFP upon the increase of the CP/DM ratio confirms that in a diet rich in fermentable energy, it is necessary to increase the dietary protein concentration and meet requirements, in order to avoid abnormalities of the physical characteristics of the milk. (C) 1998 Elsevier Science B.V.