Fiber fractions and protein content are important chemical characteristics of forage resources because of their close relationship with factors affecting the performance of dairy cows. Advances in methodologies for evaluating those characteristics and the use of indirect methods such as the near-infrared spectroscopy (NIRS) promote the chemical characterization of forage as a fundamental tool to assess the efficiency of milk production under specific conditions in production. In this study, crude protein (CP), crude ash (CA), neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) were estimated using the NIRS LOCAL algorithm in the spectrum of 1100–2500 nm every 2 nm using the FOSS NIRSystems 6500. Two hundred seventy forage resources were contextualized in terms of their topographical location (wavy, slope and flat), pasture harvest season or cut grass (rainfall, drought, rainfall-drought transition, drought–rain transition), the fertilization (yes or no) and altitude. The topography affected the CP level of the forage resources, being this lower in the slope (12.8%, P < 0.05). Harvest season affected NDF and ADF (P < 0.05). The NDF level was higher in the rainfall-drought transition compared with the drought-rain transition (57.5 vs 59.6%, P < 0.05). The ADF level was higher in the drought-rain transition compared with drought (29 vs 27.7%, P < 0.05). Fertilization affected levels of CP, CA, NDF, and ADL (P < 0.05); CP was higher when fertilization was applied to the grasslands (14.5 vs 11.4%, P < 0.05), while NDF was lower when fertilization was applied (59.2 vs 57.7%, P < 0.05). The CA level was also higher when fertilization was applied (10.6 vs 9.5%, P < 0.05), while ADL level was lower when fertilizer was applied (30.7 vs 29.4%, P < 0.05). Concentration of CP was affected by the altitude where the value was higher for samples above 2500 m above sea level. (14.2%, P < 0.001). At this level, the concentrations of NDF (55.9%) and ADL (5.2%) were lower (P < 0.001). It was concluded that the most critical variables in the determination of forages quality in dairy feeding systems are overcome taken advantage of the new technologies as NIRS.