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To evaluate the use of energy supplements from weaning to conception on multibreed heifers (Holstein (50%) x Gyr (50%) (H x G), Holstein (50%) x Jersey (50%) (H x J) y Jersey (50%) x Holstein (25%) x Gyr (25%) (J x H x G)) in a grazing dairy system under tropical conditions, the Cornell Net Carbohydrate and Protein System (CNCPS) was used. Growth curves were estimated using the logistic model (R2 = 96% on average).  The climatological conditions in the area and chemical composition of forages during the year were evaluated. With the information obtained simulations were performed and the results showed energy deficiencies between 9 and 13 months of age in the crosses studied. To correct deficiencies, supplementation alternatives were evaluated. The results indicated that sugar cane molasses and cassava flour would be feasible options to improve growth rate and reduce the age at first service (20-22 months) and first calving, reducing nutritional costs of raising heifers and total methane emission during growth.