Maintenance energy requirements of young Holstein cattle from calorimetric measurements at 6, 12, 18, and 22 months of age

Twenty five-month old Holstein cattle (10 steers and 10 heifers) were used in a four-period (28 d/period) study with measurements made at the age of 6, 12, 18, and 22 months, to evaluate effects of gender on energy utilization efficiency and maintenance energy requirement. Cattle were offered perennial ryegrass silage mixed with concentrates. In each period, the cattle were housed together in a cubicle accommodation for the first 20 d, individually in metabolism units for the next 3 d, and then in indirect open-circuit respiration calorimeter chambers for the final 5 d with feed intake, feces and urine outputs, and gaseous exchange measured during the final 4 d. There was no difference (P>0.05) in any period between gender groups in terms of growth performance, energy intake, energy output, or energetic efficiency, with the exception of period three when the steers had a greater (P<0.05) feed and energy intake than heifers. Data from the two groups were therefore pooled to develop relationships between metabolizable energy (ME) intake and retained energy (RE) for each measurement period and for the whole experimental period. Retained energy was strongly related to ME intake (P<0.001), with R2 values ranging from 0.85 to 0.93. Net energy (NE) and ME requirements for maintenance (NEm and MEm) derived from these relationships were greater for cattle at the age of 6 months than those at 12, 18, and 22 months (NEm=0.57, 0.48, 0.47, and 0.41 MJ/kg0.75; and MEm=0.78, 0.62, 0.59, and 0.63 MJ/kg0.75, respectively). These maintenance energy requirements were greater than those recommended in energy feeding systems currently used in Europe, North America, and Australia. The results indicate that current feeding systems may underestimate maintenance requirements for young dairy cattle, resulting in a reduced estimate of the efficiency of production.