Abstract
The aim of this study was to evaluate the effects of dose, start time, and application interval of recombinant bovine somatotropin (rbST) on performance, health, and reproduction parameters of crossbred Holstein × Gyr dairy cows (3/4 and 7/8). A 2 × 2 × 2 factorial study was designed to test the effects of application dose (250mg rbST or 500mg rbST), start of application (40 or 63days in milk (DIM)), and application interval (12 or 14days); 180 crossbred Holstein × Gyr cows were enrolled. Treatments with 500mg rbST resulted in increased milk production, 3.5% fat-corrected milk (FCM), and energy-corrected milk (ECM). In the factorial design analysis, greater FCM, ECM, and milk solid production (kg/day) were observed when 500mg rbST was started at 63 DIM, while 250mg rbST resulted in greater milk production (kg/day), FCM, ECM, and milk solids (kg/day) when administered at 12-day intervals. Administration of 500mg rbST resulted in an increase of days open and number of services per pregnancy (P = 0.01). Holstein × Gyr cows (3/4 and 7/8) presented a superior productive response to rbST when treated with 500mg starting at 63 DIM and at 14-day intervals.
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