Fatores não nutricionais que afetam as concentrações de nitrogênio ureico no leite de bovinos mestiços

Abstract

Among the factors that are related to milk quality, the concentration of urea nitrogen in milk (NUL) stands out. The NUL is used as a nutritional indicator in the herds, since the excess of protein in the diet, entails in high levels of NUL. However, in addition to the nutritional factors that interfere with their concentrations, NUL also suffers interference from non-nutritional factors such as body weight and birth order. High levels of NUL can lead to consequences such as reduced casein production, reproductive problems beyond environmental impact. In this way, the objective of this work was to evaluate the non-nutritional factors that interfere in the concentrations of NUL in the milk of crossbred cattle. The collections were carried out in nine properties with production between 150 and 500 L / day, the herds were composed of mestizo animals. Individual samples of 776 animals were collected in four replicates, totaling 3104 samples. On the day of collection, data on milk production (kg / day), number of lactations and body weight of the animals were also recorded, as well as considering two periods of the year, being drought period and rainy season. NUL, fat, protein, casein, lactose, total solids and CCS were analyzed. Simple linear regression analysis was performed, in addition to calculating the coefficient of determination. The mean NUL concentration was 12.58 mg / dL, fat and protein presented mean concentrations of 3.89% and 3.43% respectively, being within the limit established by the legislation. Milk production was the variable that most influenced the NUL concentration, explaining 39% of its variation, followed by protein production with 25% and solids production with 21%, while body weight had the lowest influence on or NUL. In the dry period NUL concentrations were higher than the rainy season. It was concluded that among the non-nutritional factors studied, milk production and protein production in kg were the factors that most correlated with NUL concentrations