Efecto de Niveles Crecientes de Nitrógeno no Proteico Dietario en Vacas Lactantes sobre las Concentraciones de Metabolitos Nitrogenados en Orina, Sangre y Leche Effect of Increasing Levels of non Protein Nitrogen in Dairy Cows on Nitrogen Metabolites Concentrations in Urine, Blood and Milk

Con el fin de evaluar el efecto de niveles crecientes de nitrógeno no proteico dietario (NNP) en vacas lactantes sobre las concentraciones de metabolitos nitrogenados en orina, sangre y lehe, se evaluaron 15 vacas Holstein que cursaban los primeros 100 días posparto. Estas se asignaron aleatoriamente a tres tratamientos experimentales que consistieron en el suministro de un suplemento alimenticio comercial al que se le adicionó urea de tal manera que se incrementara el consumo de proteína degradable en rumen (PDR) en aproximadamente 0,0 (T0), 10 (T1) y 15% (T2) respecto a los requerimientos. Para las 15 vacas se determinaron las concentraciones de nitrógeno ureico en sangre (NUS), orina (NUO) y leche (NUL) así como las de amonio en sangre (AS), amonio en orina (AO) y la glicemia (GLIC), utilizando kit comerciales acoplados a espectrofotometría. Se realizó un balance de PDR donde se encontraron diferencias significativas entre los tratamientos (P<0,01). El balance para la PDR representó el 2,8; 9,5 y 13,1% de los requerimientos para T0, T1 y T2, respectivamente. Se encontraron correlaciones positivas entre el NUS y el AS, y entre el NUS y el NUL; mientras que la correlación entre el NUO con el AO fue negativa (P<0,1). Las demás correlaciones exploradas no fueron estadísticamente significativas.<br>In order to test the effect of growing levels of dietary non nitrogen protein in lactating cows on urine, blood and milk nitrogen metabolites concentrations, fifteen cows Holstein in their first one hundred post calving days were used. They were three different experimental treatments assigned at random, which consisted on the supply a commercial feeding supplement without any addition of urea as a source of NNP (T0); the second treatment (T1) consisted on the supply of the same supplement with an addition of urea, so that the supply of PDR was increased 10% approximately to the requirements; finally, in the third treatment, (T2) consisted on the supply of the same supplement which was added with enough urea so that the supply of PDR was increased 15% approximately to the requirements. In these cows were determined concentrations of ureic nitrogen in blood (UNB), urine (UNU), milk (UNM), ammonium in blood (AB) and urine (AU), and glycemia; through spectrophotometric analysis. Finding positive correlations between UNB and AB and UNM, while that correlation between UNU and AU was negative. The other correlations weren't relevant. In addition, it was made a balance of degradable protein in rumen (PDR) where relevant differences were found among the treatments for the tested variables.