The expansion of agricultural frontiers in Brazil has resulted in the growth of ruminant production in the Pre-Amazon Region. However, this production is favored mainly in the rainy season, due to the greater supply of pasture for the animals. This fact limits the maintenance of production due to the lack of quality forage for the animals throughout the year. This work aimed to evaluate the nutritional value of the different sugarcane varieties for animal feeding during four crop cycles. In this experiment, the varieties RB 92579, RB 867515 and RB 863129 were studied for cane plant, first, second and third ratoons. The experiment was divided in four stages according to each cycle, and each cycle lasted approximately 10 to 11 months. For the productivity analysis and other parameters samples were collected at the end of each experimental cycle, when the dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), Brix, NDF/Brix and produtctivity were determined. The RB 92579 variety showed higher productivity (P < 0.05) in all the studied cycles, and remained above the national productivity average in all the cycles (±75 ton ha-1). This same variety, presented the best results for all nutricional parameters (DM, CP, NDF, ADF and FDN/Brix) when compared to the other varieties. The productivity/nutritional relation value must be taken into account when choosing a variety for animal feeding, being the RB 92579 variety the most expressive, during four cycles, wich lasted 4 years.

Sugarcane may be a potential feed source for ruminants in tropical and subtropical areas. An important factor that can influence the nutritional quality of sugarcane for animal feeding is nitrogen fertilization management, however, studies on this subject are still scarce. In this context, the objective of this study was to evaluate the effect of nitrogen sources on the quality and productivity of sugarcane as a forage resource. The variety of sugarcane used was RB92579, with application of nitrogen (N) sources (urea, poultry litter, swine manure) and control (without N application). Stalk productivity and dry matter, crude protein, neutral detergent fiber, acid detergent fiber, lignin, Brix, NDF / Brix ratio, and in situ digestibility were analyzed during incubation periods of 6, 24, and 72 hours. At the end of the study, it was found that the N sources did not interfere with sugarcane stalk productivity (P> 0.05), with an average productivity of 102 t ha-1. The N treatments did not influence (P> 0.05) in the nutritional quality of sugarcane, when evaluating the contents of dry matter, crude protein, neutral detergent fiber, acid detergent fiber, lignin, Brix and NDF / Brix ratio. The dry matter degradation had an effect (P <0.05) for the different N sources and incubation times, where poultry litter and swine manure treatments showed higher values for degradation at 72 hours of incubation. The different N organic sources did not interfere in the chemical composition and productivity of the sugarcane culture, however it presented better results in the in situ degradability of the dry matter. This, it can be recommended that mineral nitrogen fertilizers can be replaced by organic fertilizers.