Chemical and fermentative attributes of herbage samples collected from a natural grassland of southern Brazil: impact of period, month of the year and soil type

This study evaluated the effects of a long-term period (i.e. 2001/2002 vs 2019/2020), month of the year, soil type and their interactions on chemical and fermentative attributes of herbage samples collected through grazing simulation in a rangeland of southern Brazil. The crude protein (CP) content (dry matter (DM) basis) was on average 11.6 % and did not change between periods or months of the year, whereas was greater (P < 0.05) in the herbage present on superficial basalt-soil than in that on sandstone or deep basalt-soil type. The content of neutral detergent fiber (NDF) was on average greater (P < 0.05) in the first than in the second period (79.0 vs 69.8%) and, in both periods, the NDF content was on average greater in the herbage present on sandstone-soil than in that on superficial or deep basalt-soil type). A significant period by month interaction (P < 0.05) was observed for all parameters of in vitro gas production. On average, the volume of gas was lower in the first than in the second period (140 vs 164 ml/g DM) whereas de degradation rate (kd) was similar in both periods (average 2.52% h-1). Soil type did not affect gas volume whereas, in the first period only, the lowest and highest kd values were obtained in deep and superficial basalt, respectively (P < 0.05). In conclusion, most variables changed in the long-term period whereas only the in vitro degradation variables showed significant changes throughout the year.