Relationships Between Blood Urea Nitrogen and Energy Balance or Measures of Tissue Mobilization in Holstein Cows During the Periparturient Period

Our objective was to determine if blood urea nitrogen (BUN) is related to calculated energy balance (EB) or a measure of tissue mobilization during the periparturient period. Blood samples were collected from 41 cows with varying postpartum EB and analyzed for BUN and nonesterified fatty acids (NEFA). The cows were fed the same diets throughout the experimental period. Although there was no relationship between BUN and EB or plasma NEFA at 2 wk prepartum and 1 wk postpartum, there was a relationship between BUN and plasma NEFA at wk 2 postpartum, and there was a tendency for BUN to be related with feed efficiency, BW, and postpartum BW loss at wk 2 postpartum. Although NEFA alone predicted only 14% of the BUN variation, feed efficiency, BW, and BUN, collectively, were reliable predictors of tissue mobilization in dairy cows in early lactation (R2 = 0.65).