Interactive Effects of Nitrogen Fertilization and Harvest Age on the Nutritional Composition of Brachiaria ruziziensis

High-quality forage is vital for livestock productivity, but farmers in Nigeria often face challenges due to inconsistent fertilizer use and poor harvesting practices. This study evaluates the effects of nitrogen fertilizer rates and harvest age on the nutritive value of Brachiaria ruziziensis to enhance forage quality and support sustainable livestock nutrition. A 3 × 2 factorial design was used, testing three fertilizer rates (0, 120, and 240 kg N ha-1 as NPK 15:15:15) and two harvest ages (8 and 10 weeks after planting), resulting in six treatments. Proximate composition, fiber fractions, forage quality indices, mineral content, in vitro gas production, and post-incubation parameters were analyzed using standard laboratory methods. Both fertilizer rate and harvest age significantly (P < 0.05) influenced dry matter (DM), crude fiber (CF), crude protein (CP), ether extract (EE), ash, non-fiber carbohydrates (NFC), and metabolizable energy (ME). Fiber components, including acid detergent fiber (ADF), hemicellulose, and cellulose, were also affected. Forage quality indices such as organic matter (OM), carbohydrate content (CHO), dry matter digestibility (DMD), dry matter intake (DMI), relative feed value (RFV), cell content (CC), total digestible nutrients (TDN), and net energies for intake, gain, maintenance, and digestible energy showed significant improvements with increased fertilizer rates and earlier harvest. Mineral contents—sodium (Na), calcium (Ca), phosphorus (P), potassium (K), manganese (Mn), iron (Fe), and copper (Cu)—varied significantly with treatments. In vitro gas production and post-incubation parameters also showed significant differences. The study concludes that applying NPK 15:15:15 at 120 kg N ha¹ and harvesting at 8 weeks after planting optimizes biomass yield and improves proximate, fiber, mineral content, and forage quality, making it a cost-effective and sustainable approach for pasture management in Nigeria.