ABSTRACT This study was performed to identify the ideal amount of concentrate required for a diet based on cactus cladodes, sugarcane, and urea used to feed heifers. Twenty Girolando heifers (160±8.39 kg) were randomly distributed into four experimental treatments with 0, 0.40, 0.80, or 1.20 kg day−1 of concentrate. The basal diet contained [on dry matter (DM) basis] 38.1% sugarcane, 56.5% cactus cladodes [ Opuntia stricta (Haw). Haw.], 0.5% common salt, 1.1% mineral mixture, and 3.8% urea plus ammonium sulfate. The concentrate contained [on DM basis] 87% corn meal and 13% soybean meal. The basal diet and the concentrate were formulated to provide 13% crude protein (CP). The intake of DM (4.34-4.96 kg day−1), organic matter (3.96-4.98 kg day−1), CP (0.57-0.64 kg day−1), non-fibrous carbohydrates (2.20-2.61 kg day−1), and metabolizable energy (10.3-12.4 Mcal day−1) increased linearly with concentrate amount. Final body weight (196-224 kg), total body weight gain (36.9-61.2 kg), and average daily body weight gain (0.51-0.85 kg day−1) increased linearly with concentrate amount. The nitrogen balance was positive and increased linearly (54.8-62.3 g day−1) with concentrate amount. Based on the data, we recommend supplying six-month-old Girolando heifers (160 kg body weight) 1.20 kg concentrate day−1 added to a diet based on sugarcane and cactus cladodes plus urea for better productive and economic performance.

Resumo: O objetivo deste trabalho foi avaliar o efeito de diferentes níveis de bagaço de cana-de-açúcar, como volumoso exclusivo, sobre consumo e digestibilidade de nutrientes, comportamento ingestivo, síntese de proteína microbiana e desempenho leiteiro de vacas mestiças. Dez vacas da raça Girolando (600±34,3 kg de peso corporal) foram distribuídas em delineamento de quadrado latino duplo 5×5. A dieta controle, baseada em palma forrageira, bagaço de cana-de-açúcar e concentrado, foi formulada para atender a média de produção de 20 kg de leite por dia, com 3,5% de gordura. Foram avaliados os seguintes níveis de bagaço de cana-de-açúcar: 30, 38, 46 e 54% da matéria seca. O consumo e a digestibilidade de matéria seca diminuíram linearmente com os níveis de bagaço. O tempo de ruminação foi maior para vacas alimentadas com 54% de bagaço. Os níveis de inclusão não tiveram efeito sobre o conteúdo de ácidos graxos não esterificados ou sobre a síntese de proteína microbiana, mas as concentrações de β-hidroxibutirato apresentaram comportamento quadrático com os níveis de bagaço. Maiores produções de leite corrigido a 3,5% de gordura foram obtidas com vacas alimentadas com 30% de bagaço. A inclusão do bagaço de cana-de-açúcar na dieta de vacas mestiças reduz seu desempenho; contudo, o bagaço pode ser utilizado como volumoso exclusivo quando associado a 70% de concentrado.

Abstract: The objective of this work was to evaluate the effects of different levels of sugarcane bagasse, as exclusive roughage, on nutrient intake and digestibility, feeding behavior, microbial protein synthesis, and dairy performance of crossbred cows. Ten lactating Girolando breed cows (600±34.3 kg body weight) were assigned to a replicated 5×5 Latin square design. The control diet, based on spineless cactus, sugarcane bagasse, and concentrate, was formulated to meet the average production of 20 kg of milk per day, with 3.5% fat. The evaluated levels of sugarcane bagasse were: 30, 38, 46, and 54% dry matter bases. The intake and digestibility of dry matter decreased linearly with sugarcane bagasse levels. Rumination time was higher in cows fed 54% sugarcane bagasse. The inclusion levels had no effect on non-esterified fatty acid contents or on the efficiency of microbial protein synthesis, but beta-hydroxybutyrate concentrations showed a quadratic pattern to the bagasse levels. Higher yields of 3.5% fat-corrected milk were obtained with cows fed 30% sugarcane bagasse. Sugarcane bagasse inclusion in the diet of crossbred dairy cows decreases their performance; however, the bagasse can be used as exclusive roughage when associated with 70% concentrate.