ABSTRACT Body development and reproductive performance of a hundred forty-two 14 to 15-month-old heifers, classified at weaning according to frame size as small, medium, and large, were evaluated. The parameters evaluated were: body weight, hip height, body condition score, weight gain, ovarian activity, and pregnancy rate. At weaning, body weight and hip height were significantly different among frame scores, (small – 133.0 kg, 92.2 cm; medium – 158.5 kg, 96.6 cm; and large – 185.2 kg; 100.2 cm). After weaning, heifers grazed together on natural pastures during the autumn and on ryegrass (Lolium multiflorum La.) during the winter and spring. Frame score differences remained until the beginning of the breeding season (BS), starting on average at 14 months of age. Weight gain between weaning and the beginning of BS was not different among frame scores (0.740 kg/day, on average). Body weights at the beginning of the BS were significantly different, of 255.7 kg (53.3% of the mature weight) for small heifers, 285.0 kg (59.4%) for medium heifers, and 307.6 kg (64.1%) for large heifers. Ovarian activity at the beginning of the BS was not different among the three groups. The average weight gain values during the BS of 0.492, 0.472, and 0.421 kg/day for small, medium, and large heifers, respectively, were significantly different. Pregnancy rates were not different among groups (small, 71.4%; medium, 76.4%; and large, 76.5%). Frame score did not influence the reproductive performance of heifers, but the small and medium heifers conceived 29 and 20 days earlier, respectively, than the large heifers.

Avaliou-se o desempenho de novilhas de corte até o parto submetidas a diferentes níveis de suplementação em pastagem natural durante o primeiro período reprodutivo, dos 14 aos 17 meses. Foram utilizadas 98 novilhas contemporâneas do mesmo rebanho dos grupos genéticos Charolês, Nelore e suas cruzas, com peso médio de 255 kg. As novilhas foram distribuídas em três grupos: sem suplementação; com suplementação de 3,5 g/kg do peso corporal; com suplementação de 7,0 g/kg do peso corporal. O peso ao final e o ganho de peso médio diário durante o período de suplementação foi maior entre as novilhas do grupo com suplementação na proporção de 7,0 g/kg (322 e 0,701 kg) em comparação àquelas sob suplementação na proporção de 3,5 g/kg (302 e 0,464 kg) e sem suplementação (288 e 0,425 kg), que não diferiram entre si. O escore de condição corporal ao final da suplementação diferiu entre os três grupos com 3,07; 3,33 e 3,47 pontos, respectivamente, para novilhas sem suplementação; com suplementação na proporção de 3,5 g/kg do peso corporal; com suplementação na proporção de 7,0 g/kg do peso corporal. A porcentagem de prenhez foi influenciada significativamente pelo nível de suplementação, sendo de 35,0; 34,2 e 70,0%, respectivamente. Os dois grupos sob suplementação tiveram maior taxa de concepção na metade inicial do período reprodutivo. A média de idade das novilhas ao parto foi de 785, 778 e 761 dias, respectivamente. O ganho médio diário e a condição corporal foram semelhantes entre as novilhas dos dois grupos genéticos, porém o peso ao início e ao final do período de suplementação foi maior nas filhas de touros charoleses em relação às de touros nelores, refletindo-se nas taxas de manifestação de estro (68,8 vs. 38,2) e de prenhez (60,9 vs. 26,5). As características relacionadas ao parto das novilhas não foram influenciadas pelos níveis de suplementação durante o período reprodutivo. A suplementação durante o período de acasalamento aumenta o desempenho reprodutivo de novilhas aos 14 meses de idade.

The objective was to evaluate the performance of beef heifers until calving receiving different levels of supplementation on native pasture during the first breeding season, from 14 to 17 months: no supplementation; 3.5 g/kg of body weight; and 7.0 g/kg of body weight. Ninety-eight Charolais, Nellore and their crosses, with average initial weight of 255 kg, were used. Weight at the end and average daily weight gain during the supplementation period were higher for 7.0 g/kg of supplement heifers (322 and 0.701 kg) compared to those with 3.5 g/kg of supplement (302 and 0.464 kg) and heifers without supplementation (288 and 0.425 kg), which did not differ from each other. Body condition score at the end of the supplementation was different between the three treatments, being 3.03, 3.33 and 3.47 points for heifers without supplementation; 3.5 g/kg of body weight; and 7.0 g/kg of body weight, respectively. Pregnancy rate was significantly affected by supplementation level, being 35.0, 34.2 and 70.0%, respectively. Heifers of the two supplementation treatments had higher conception rate at the first half of the reproductive period. Average heifer ages at calving were of 785, 778 and 761 days, respectively. The average daily weight and body condition of the heifers of the two genetic groups were similar; however, the initial and final weight of the supplementation period was higher for Charolais bulls daughters, compared with Nellore bulls daughters, reflecting on the heat (68.8 vs. 38.2%) and pregnancy (60.9 vs. 26.5%) rates. Characteristics related to calving were not affected by the supplementation levels during the reproductive period. The supplementation during the first breeding season increases reproductive performance of heifers at 14 months of age.