The objective of the present study was to evaluate the effect of increasing levels of prepartum and postpartum protein supplementation on nutrient intake and digestibility, productive performance and metabolic status of beef heifers on tropical pasture. Twenty-eight pregnant beef heifers with bodyweight and body condition score of 459.7 ± 6.8 kg and 5.8 ± 0.10 respectively, were used. The experiment was performed according to a completely randomised design, with the following four treatments: 0.0, 0.4, 0.8 and 1.2 kg/animal.day of protein supplement containing 25% crude protein. All animals received a mineral mixture ad libitum. The experiment lasted 210 days, divided into three experimental periods. The supplementation level increased the intake of all evaluated nutrients, digestibility of organic matter, neutral detergent fibre corrected for ash and protein, as well as higher average daily gain prepartum and bodyweight of calves at birth (P < 0.05). Protein supplement at the levels evaluated did not affect body condition score (P > 0.05). An interaction effect between treatment × days in relation to calving occurred for concentrations of serum urea nitrogen, total proteins, albumin and globulins (P < 0.05). Supplementation did not affect glucose, triglyceride, non-esterified fatty acids, β-hydroxybutyrate or progesterone (P > 0.05). In conclusion, supply of up to 1.2 kg/day of protein supplement for grazing beef heifers optimises forage intake and average daily gain before calving, and improves the indicators of the protein status.

ResumoObjetivou-se avaliar os efeitos de suplementos múltiplos com diferentes fontes protéicas sobre o desempenho produtivo, consumo, digestibilidade dos componentes da dieta e eficiência de síntese de proteína bruta microbiana de bezerras de corte lactentes sob pastejo. O trabalho foi realizado durante o período de transição de águas-secas (Fevereiro á Julho de 2012), utilizando-se quatro piquetes com média de 4,5 há; para tal, foram utilizadas vinte quatro bezerras com idade e peso médio inicial de 3 meses e 113 kg, respectivamente. Os tratamentos foram: mistura mineral (MM) ad libitum, farelo de soja (PB FS ), farelo de algodão 38% de Proteína bruta (PB FA ) e combinação de farelo de soja com farelo de algodão 38% de Proteína bruta (PB FS+FA ). Não se verificou efeito (P>0,10) das diferentes fontes protéicas sobre o ganho médio diário (GMD) entre os animais que receberam suplementos múltiplos, assim como não foi verificado diferença no GMD entre os suplementados com suplemento múltiplo e suplementados apenas com mistura mineral. Sendo assim, o farelo de algodão pode substituir o farelo de soja ou ser utilizado em associação ao farelo de soja em suplementos múltiplos para bezerras de corte lactentes. Palavras-chave: Creep-feeding, bezerros, desempenho, lactentes AbstractThe aim of this study was to evaluate the effects of multiple supplements with different protein sources on the performance, intake, nutrient digestibility, and microbial protein production efficiency of lactating beef heifers under grazing. The experiment was carried out during the period of transition from water-dry (February to July, 2012) using four paddocks with average of 4.5 ha. Twenty four lactating beef heifers with initial body weight of 113 kg and 3 month old, were used. The treatments were: mineral mixed (MM) ad libitum, soybean meal (SM), cottonseed meal 38% crude protein (CM), and combination of SM and CM (SMCM). There was not observed effect (P>0.10) of different protein sources on average