Semina: Ciências Agrárias, Londrina, v. 37, n. 4, p. 2221-2234, jul./ago. 2016 Aguilar, P. B. et al. quatro tratamentos (doses de nitrogênio) e quatro repetições (número de piquetes adubados). Foram utilizadas 16 novilhas da raça Nelore, com média de oito meses de idade e com peso corporal inicial de 178,69 ± 26,67 kg, sendo quatro novilhas por tratamentos. Os resultados foram avaliados por meio de análise de variância e regressão a 5% de probabilidade. As atividades comportamentais dos animais não se alteraram (P>0,05) com o uso das diferentes doses de nitrogênio nos pastos com tempos médios de 576,25 minutos (10h:00min) em pastejo, 509,84 minutos (8h:50min) em ruminação, 315,16 minutos (5h:25min) em ócio e 39 minutos alimentando no cocho. Para o nitrogênio ingerido, nitrogênio digerido e o nitrogênio retido (g/dia) e o nitrogênio digerido (% do N ingerido), houve efeito linear crescente (P<0,05) em função das doses de nitrogênio. Para o nitrogênio ureico na urina, houve efeito linear crescente (P<0,05) com incremento de 0,335 mg/dL para cada 1 kg de N aplicado. Para o nitrogênio ureico no plasma não houve efeito (P>0,05) das doses de nitrogênio, com média de 15,79 mg/dL. As atividades comportamentais das novilhas não são afetadas pelas doses de nitrogênio em pastos de Urochloa brizantha cv. Marandu diferidos. O nitrogênio ingerido, nitrogênio retido (g/dia), o nitrogênio digerido (g/dia) e (% do N ingerido), a concentração de nitrogênio ureico na urina, e as excreções de ureia e de nitrogênio ureico na urina são influenciados pela quantidade crescente de proteína bruta na forragem oriundas da adução nitrogenada, nas condições de realização desta pesquisa. Palavras-chave: Adubação nitrogenada. Diferimento. Tempo de pastejo. Ureia. Urina.

The use of agroindustrial byproducts in cattle diets, such as castor-bean (Ricinus communis L.) meal, is a more sustainable practice because it does not compete with human food and reduces the volume of organic waste deposited in the environment. The aim of this study was to examine the effect of replacing soybean (Glycine max (L.) Merr.) meal with castor-bean meal on the intake, digestibility, feeding behavior and performance of crossbred steers supplemented while on Urochloa brizantha (Hochst. ex A. Rich.) R.D. Webster 'Marandu' pasture. The experiment was laid out in a randomized complete design with 40 animals, which started the experiment weighing 227.1 kg, at 10 mo of age, and were divided into four treatment groups. Castor-bean meal was added to replace soybean meal at the levels of 0, 90, 180, and 280 g kg -1 in the supplement, which was supplied at the rate of 0.4% of body weight. Total DM, pasture DM and neutral detergent fiber intakes did not change (P > 0.05) with the castor-bean levels added to the supplement. Ether extract intake and digestibility decreased linearly (P < 0.05). The animals showed no differences (P > 0.05) in production performance (average daily gain), which averaged 0.65 kg d -1 . Grazing, idle, and rumination times were not influenced (P > 0.05) by the treatments. Castor-bean meal can be included up to 280 g kg -1 in the total diet without changing the performance of crossbred steers finished on tropical pasture.

This study examined different levels of replacement of soybean meal with detoxified castor bean meal in the finishing of crossbred steers on Brachiaria brizantha cv. Marandu pasture during the rainy-dry transition period. Forty Holstein-Zebu crossbred steers with an average initial weight of 395.93 ± 10 kg were randomly allocated to four treatment groups that were supplemented with concentrate containing different levels of castor bean meal replacing soybean meal (0, 30, 60, or 90%; at 0.4% body weight [BW]). The experimental period was 112 days. A completely randomized experimental design was adopted; with regression analysis conducted using the Statistical and Genetic Analysis System (SAEG). Intake and digestibility of dry matter (DM) and nutrients and animal performance were evaluated. The replacement of soybean meal with castor bean meal did not influence (P>0.05) the intakes of DM (kg day-1), organic matter (OM, kg day-1), neutral detergent fiber (NDF, kg day-1 and %BW), non-fibrous carbohydrates (NFC, kg day-1), or total digestible nutrients (kg day-1). However, the intakes of crude protein (CP) and ether extract (EE, kg day-1) decreased as the replacement levels were increased (P<0.05). The digestibility of DM, OM, NDF, and EE did not change, whereas CP digestibility decreased linearly and NFC digestibility increased linearly (P<0.05). The replacement levels did not affect (P>0.05) final live weight, average daily gain, feed conversion, or carcass yield. Detoxified castor bean meal can replace up to 90% of soybean meal in the composition of the supplement without compromising the production performance of steers on Brachiaria brizantha cv. Marandu pasture during the rainy-dry transition period.