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This study identified the relationship between energy balance and some blood metabolites in primiparous dairy cows with different calving conception interval. Twenty primiparous Holstein-Friesian dairy cows were grouped according to the interval (days) from calving to conception into early-conception (early-c; <100 days), mid-conception group (mid-c; 100 -- 150 days) or late-conception (late-c; >150 days) group; and evaluated on day -7 prior to parturition, and days 28, 56 and 90 postpartum. All groups presented positive energy balance, serum concentrations of HDL, urea-N and progesterone with no difference on days 28 and 56 of lactation. On day 90 of lactation all the cows presented negative energy balance; however, the early-c group presented a less intense (P < 0.05) net energy balance (-1.09 versus -2.15 and -1.86 Mcal/day), lower concentrations of serum urea-N (3.28 versus 4.22 and 4.88 mg/dL) and HDL cholesterol (0.84 versus 1.59 and 1.46 mmol/L) and greater serum concentration of progesterone (8.13 versus 4.54 and 1.83 ng/mL) than cows of mid-c and late-c groups, respectively. In conclusion, different from those usually observed for multiparous dairy cows, the energy balance during the first weeks of lactation was not a determining factor affecting the calving conception interval of primiparous dairy cows in the present study. Instead, the nutritional status and the serum concentration of urea-N and progesterone at a later stage, after 56 days of lactation, suggest having a role in delaying these cows' pregnant status. [ABSTRACT FROM AUTHOR]