Understand how forage quality in semi-arid rangelands is modified by the botanical composition and climatological factors is essential for the appropriate nutritional management of the livestock. This study investigated the influence of the vegetal stratum and season on the bromatological composition of the forage in rangelands from a seasonally dry tropical forest in the Brazilian semi-arid. The experimental design was completely randomized with five replications, and the treatments consisted of two vegetal strata (herbaceous and shrub-arboreal), and two seasons (rainy and dry), in a two-year field trial. There was a significant effect of the season on the crude protein, fiber, hemicellulose, lignin, and soluble carbohydrates (p < 0.05), and the forage showed lower nutritional value during the dry season. Forage dry matter content was greater in the dry season (p < 0.05). There was a pronounced effect of the type of vegetation on the crude protein, fiber, hemicellulose, lignin, total and soluble carbohydrates (p < 0.05), and the herbaceous vegetation was characterized by greater content of fiber compounds and total carbohydrates, while the shrub-arboreal stratum by greater crude protein, soluble carbohydrates, and lignin. The cellulose content was greater in the herbaceous stratum (p < 0.05). The shrub-arboreal strata had greater contents of ether extract (5%), compared to the herbaceous vegetation (1%) (p < 0.05), and it was intensified by the dry season. Despite the mutual influence of the season and the vegetal strata on the bromatological composition of the forage, the type of vegetation of the semi-arid rangelands had a stronger effect in defining forage quality.

了解半干旱牧场的草料质量如何受到植物成分和气候因素的影响，对于适当的牲畜营养管理至关重要。本研究调查了植物层和季节对巴西半干旱地区季节性干燥热带森林牧场草料植物学组成的影响。在为期两年的田间试验中，实验设计完全随机，重复五次，处理包括两个植被层（草本和灌木-乔木）和两个季节（雨季和旱季）。季节对粗蛋白、纤维、半纤维素、木质素和可溶性碳水化合物的影响显着（p < 0.05)，且牧草在旱季表现出较低的营养价值。干季牧草干物质含量较高（p  < 0.05）。植被类型对粗蛋白、纤维、半纤维素、木质素、总碳水化合物和可溶性碳水化合物的影响显着（p  < 0.05），草本植被的特征是纤维化合物和总碳水化合物含量较高，而灌木-树栖地层中含有较多的粗蛋白质、可溶性碳水化合物和木质素。草本层中纤维素含量较高（p  < 0.05）。与草本植被 (1%) 相比，灌木-乔木地层的乙醚提取物含量更高 (5%) ( p < 0.05)，旱季加剧。尽管季节和植物地层对牧草的营养学组成有相互影响，但半干旱牧场的植被类型对定义牧草质量有更大的影响。