This study aimed to evaluate the nutritive value of sugarcane silage at different harvest seasons and treated with additives, as well as its estimation by near-infrared reflectance spectroscopy. The experiment was developed in Colorado do Oeste, RO, Brazil, being adopted a completely randomized design with four repetitions. The treatments were arranged in a 3´5 factorial scheme, being: three harvest seasons (March, May and July); and five additives: 10% corn flour; 10% disintegrated straw and cob corn; 15% rice bran; 1,0% urea; no additive. Dry matter, crude protein, neutral detergent fiber, acid detergent fiber, ash, indigestible neutral detergent fiber and estimated total digestible nutrients contents were evaluated. The nutritive value of sugarcane silage improves with additives, when compared to sugarcane silage in natura. The moisture sequestering additives present better results when compared to urea, with the exception of crude protein content. The co-product rice bran provides reduced fiber content, and increased crude protein and total digestible nutrient contents of the silage. The silage produced in July and with additives provides the highest contents of total digestible nutrients. The near-infrared reflectance spectroscopy estimates are excellent (R2cv > 0.95) for crude protein, neutral detergent fiber, acid detergent fiber, and ash, offering ranchers and researchers a fast and inexpensive service.