The objective of the study was to analyse the effect of enriching milk replacers with crude protein (CP) and/or gross energy (GE) on rearing performance of Polish Holstein-Friesian heifer calves. The study was a 2 × 2 factorial design, with the two factors being CP content (220 and 290 g) and GE content (21 and 23 MJ) of milk replacer dry matter (DM). Thirty-two heifer calves aged 7 days were assigned to 1 of 4 experimental groups (n=8), in which they received limited milk replacer (800 ±10 g DM × day-1) to 56 days of age and the same concentrate mixture ad libitum to 120 days of age. Feeding programme and nutritive value of concentrate mixture were applied as recommended by IZ PIB-INRA feeding standards (2009). Rearing performance was determined from body weight and body size measures at 7, 56 and 120 days of age, and feed and nutrient utilization for weight gain and body size gain during the periods from 7 to 56, 57 to 120 and 7 to 120 days of age. During the liquid feeding period from 7 to 56 days of age, the increase in CP concentration in milk replacers had a statistically significant effect on weight gains, body size (P≤0.05), and utilization of feed DM, CP and GE for weight gain (P≤0.05), while the increase in GE concentration improved daily weight gains and utilization of CP for weight gain (P≤0.05). The increase in CP concentration and the simultaneous decrease in GE concentration had a beneficial effect on the intake of concentrate mixture (statistical tendency, P≤0.1), but its utilization for weight gain was similar in all the experimental groups. Heifer calves that had received protein-rich milk replacers previously, during the period from 57 to 120 days of age ingested more concentrate mixture per day but were less efficient in nutrient utilization for weight gain (statistical tendency, P≤0.1).
