Energy requirements of Holstein, Gyr, and Holstein × Gyr crossbred heifers using the respirometry technique

We aimed to determine the energy requirements for maintenance and gain of 18 prepubertal dairy heifers three breed compositions (BC; Holstein, Gyr, Holstein × Gyr). Diets were formulated gains 0, 400, 800 g/day, corresponding 1.0×, 1.5×, 2.0× maintenance, respectively. Each BC had six animals with an initial body weight (iBW) 219.8 ± 32 kg, 215.8 33 228.3 kg The experiment was designed as a completely randomized design in factorial scheme 3 [three feeding levels (FL)]. Digestibility metabolism assays performed losses through feces urine. Heat production determined using continuous measurement oxygen consumption, carbon dioxide production, methane emissions respiration chambers. Energy (NEm) calculated based on relationship between heat (HP) metabolizable intake (MEI). efficiency use ( k m ) obtained from ratio NEm maintenance. net growth (NEg) estimated model RE = β 0 EBW 0.75 EBG β1 , where is retained (Mcal/day), empty (kg ), (kg/day). g slope regression MEI gain. Gyr presented 15% lower (98 kcal/kg BW than HG crossbred animals. similar NEm, 102 112 0.71, 0.74, HG, Net requirement did not differ across BC, single equation fit all BC: 0.069 BGW 0.852 . A 0.65 observed BC. Breed composition affected partition, those differences should be considered when estimating crossbred, heifers.