AbstractThree groups of 24 Holstein heifers of breeding age were grazed at 5 animals per ha on intensively managed pastures at the Isabela Substation. Treatments differed in concentrate supplementation as follows: T1, none (control); T2, 1.8 kg per head daily continuously; and T3, 4.5 kg daily to heifers beyond 5 months pregnant. About 2 kg per head daily of poor-quality hay was supplied when drought reduced pasture herbage availability. Groups remained intact for 309 days; thereafter, heifers nearing parturition were removed periodically until final termination after 449 days. Respective mean liveweights increased from 339, 334, and 330 kg initially to 468, 517, and 465 kg after 309 days, representing daily increments of .42, .58, and .44 kg; treatments T2 and T3 combined surpassed T1, and T2 surpassed T3 (P < .01). Corresponding gains including data beyond 309 days, of .46, .59 and .50 kg, also differed (P < .01). Treatments significantly affected final measures of heart girth and body length (P < .01), but not wither height. In T2 and T3, 9.64 and 4.25 kg of concentrate were employed per kilogram extra gain (relative to control). T2 resulted in earliest establishment of pregnancy (P < .01). Follow-up observation was possible on only 18 animals transferred to the Lajas Substation; those fed concentrate prepartum (T2 and T3) produced 10% more milk in first location and had lower attrition rate than controls. Concentrate supplementation beyond breeding age is an expensive means of accelerating growth and achieving earlier calving, but may be necessary for optimum postpartum performance.
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