Consumption, digestibility and cattle condition according to forage composition and quality in maize-cattle from conservation-based agroecosystems

The cereal-cattle conservation-based agroecosystems in neotropical savannas are based on the introduction of a forage of better quality than that of the native pasture. This forage acts as a soil protective coverage under non-tillage managements and like green manure to the maize culture. In order to evaluate how the consumption by bovine, digestibility and animal condition changes in these agroecosystems, we study, during a grazing cycle (110 days in the dry season), the following: total aerial biomass (TAB), green leaf biomass (GLB), fiber content of the leaves (lignin, ADF and NDF), botanic composition of the cattle excreta by microhistological analysis, N-NH3 content in the cattle rumen and the presence of urea in blood. The introduced species were Brachiaria dyctioneura grass (Bd) and Centrosema macrocarpum legume (Cm), both perennials, associated to maize for 4 years of non-tillage management and alternative phosphorus sources. During the grazing period, the level of N-NH3 in the rumen was 12.1 mg/L and 16.6 mg/L in the animals of the agroecosystems Bd and Cm, respectively. In the case of urea in blood, the concentration was significantly higher under legume (24.6 mg/dL) compared to the grass (9.7 mg/dL). Daily weight gain favored Bd (0.68 kg/d) > Cm (0.29 kg/d) > NS (−0.006 kg/d). Body condition was significantly higher in introduced pastures compared to NS. At this time, the microhistological studies of the cattle excreta showed a significant variation of the Bd and Cm consumption, selecting as second option Andropogon gayanus and maize (Zea mays) residues in a higher percentage, depending of the dominant cover crop. Thus, the digestibility was related to the appearance frequency of these species (p < 0.01). The GLB of Cm decreased significantly during the grazing. At the same time, the lignin content increased in both cover crops, influencing the consumption, digestibility and daily weight gain (DWG) of the cattle in the agroecosystems, compared to savanna ecosystem.