Nitrogênio uréico no leite de vacas mantidas em pastagens de aveia e azevém

Abstract

Milk urea nitrogen (MUN) is derived from protein metabolism as well as ammonia formed with the rumen. MUN can be used to estimate Blood Urea Nitrogen (BUN). The ammonia which is formed in the rumen and is not utilized in bacterial metabolism is absorbed by rumen wall and trnsformed into urea in the liver The objective of the present paper evaluate a possible protein excess in the diet of dairy herds through MUN levels. A total of 598 animals from 11 different herds were sampled. Also, feed consumed was sampled for analyses and individual cow production recorded. In milk samples, fat, protein, lactose, total solids, somatic cell count and MUN were measured. MUN was related positively related to total protein consumption and negatively related to total energy, which is demonstrated by the equation NUL=0.87 + 7.2PI 0.31ET and P<0,001. When the herds are blocked by production (Group 1 < 15 L; Group 2 between 15 and 25 L; and Group 3 > 25 L) there is a difference in protein and energy consumption, however, NUL was not different between groups 2 and 3. When production is considered, the correlation yields the equation NUL=3.39 + 5.68PI - 0.62 ET + 0.43 Prod and P<0,0001. Based on the results it is concluded that in RS state, NUL is elevated during winter months, principally in higher producing herds.