G.L. Arzate-Vázquez, F.A. Castrejón-Pineda, R. Rosiles-Martínez, S. Carrillo-Pita, S. Angeles-Campos, and E. Vargas-Bello-Pérez. 2016. Effect of genus and growth stage on the chemical and mineral composition of tropical grasses used to feed dairy cows. Cien. Inv. Agr. 43(3): 476-485. In tropical production systems, dairy cows are rarely supplemented with minerals, which often lead to mineral imbalances. Grasses grown together in the same soil type and sampled at the same growth stage can vary widely in chemical and mineral composition; therefore, the objective of this study was to characterize the chemical and mineral composition of Urochloa spp., Megathyrsus spp., and Andropogon spp. at three different stages of growth in the same soil type. The content of dry matter (DM; g 100 g-1) was higher (P<0.05) in Urochloa spp. than in Andropogon spp. and Megathyrsus spp. Hemicellulose, non-fiber carbohydrates and slowly degraded true protein contents were higher (P&#8804;0.05) in Andropogon spp. than in Urochloa spp. and Megathyrsus spp. Ether extract, crude protein, rapidly degraded true protein and unavailable protein contents were not affected by genus, whereas ether extract, ash, neutral detergent fiber, non-fiber carbohydrates, rapidly degraded true protein and unavailable protein contents were not affected by growth stage. Compared with Urochloa spp. and Andropogon spp., Megathyrsus spp. had higher (P&#8804;0.05) contents of Na and Mg, intermediate (P&#8804;0.05) contents of Mn and lower (P&#8804;0.05) contents of Zn. P, Na, and K contents were affected by growth stage. Compared with Megathyrsus spp. and Andropogon spp., Urochloa spp. was higher (P&#8804;0.05) in P and Na contents. Results from this study may be useful in predicting the nutrient and mineral supply from forages in dairy production systems in tropical areas.