Valor nutritivo de gramíneas forrageiras exóticas sob incidência de espécies espontâneas no agreste de Pernambuco

Abstract

In the livestock production of semiarid areas from Northeast-Brazil predominates the use of native vegetation of the region as the base of animal nutrition, in general the native pastures of this region have low carrying capacity. With the intensification of animal production systems, there is a natural demand for replacement of native forages with low potential for species with higher yield and superior nutritional quality. Cultivation of exotic grass species have been stimulated in the semiarid region of the Northeast. This study evaluated botanic composition of the pasture and the nutritive value of four promising exotic grasses to semiarid region of Agreste of Pernambuco: sabi grass (Urochloa mosambicensis Hackel Dandy), buffel grass (Cenchrus ciliaris L.); pangola grass (Digitaria pentzii Stent) and Panicum maximum Jacq. (spontaneous genotype in the region). The treatments were evaluated in grazing cycles. In the study of the botanical diversity, the pastures were assessed for their susceptibility to occurrence of weed species by mass comparison, and by the fluctuation of their botanical composition during a grazing season. In general, the grasses decline their forage mass over the grazing cycles, weed species tended to increase their mass in buffel grass pasture. The sabi grass appears to have an ability to suppress weeds even when this grass had low forage mass. The pastures of exotic grasses in the Agreste region were strongly affected by shrub weeds, especially those belonging to the Malvaceae family. The specie Sidastrum paniculatum (L.) Fryxell proved to be a potential weed to the pastures of this region. In pasture samples obtained by simulated grazing were analyzed: dry matter (DM), crude protein (CP); neutral detergent fiber (NDF), acid detergent fiber (ADF); lignin and in vitro digestibility of DM (IVDMD). Among the chemical characteristics analyzed NDF, ADF and lignin tended to vary substantially among species when they were under grazing. Buffel grass presented during the grazing and deferment, low coefficients of IVDMD (44.79 and 50.17%, respectively) and higher NDF percentage (68.55%) and lignin (3.74%) during the grazing period, was the specie with lowest nutritional value among evaluated species. Pangola grass stood out qualitatively by low NDF (54.3%) and high IVDMD (64.2%) during the grazing period. Among the grasses evaluated, pangola grass and P.maximum demonstrated potential in a nutritional perspective, for being used in animal production systems in the Agreste region of Pernambuco.