Caracterização da vegetação, desempenho e seletividade de ovinos em caatinga raleada sob lotação contínua, Serra Talhada-PE

Abstract

The Caatinga is an important forage resource for the herd of Brazilian semiarid region. This study aimed to characterize the vegetation and animal performance, as well as the sheep selectivity throughout the year in thinning Caatinga in Serra Talhada-PE. The research included evaluation of vegetation and animal performance (sheep) at 38 hectares of Caatinga in a private farm. A fraction of the vegetation was previously thinned for cultivation of corn, beans and sorghum, and replaced by Cenchrus ciliaris L. and Urochloa mosambicensis Hack. Currently, the rangeland is used by crossbred sheep (Dorper x Santa Inês) which stay in the area during the year, at a fixed stocking rate. Response variables included herbage mass, herbage chemical composition, percentage of bare soil, plant height, percentage of litter, stocking rate, animal performance, herbage allowance, botanical composition of the rangeland and of the diet, and selectivity index. Herbage mass ranged from 422 ± 42 to 1262 ± 95 kg DM.ha-1 from January/2011 to January/2012, which led to decreased herbage allowance (5.1 ± 0.5 to 24.5 ± 1.8 kg DM/kg BW), along the season. The weight gain of the sheep was 2.0 ± 2.2 kg/head/period and 3.8 ± 4.0 kg/ha/period. The percentage of litter was higher at October/2011 (38.8 ± 4.1%) and January/2012 (41.4 ± 4.3%). High percentage of bare soil was observed, especially during the dry season, showing average 24.4 ± 1.5%, being higher than in January/2011 with 43.6 ± 5.9% and increased throughout the dry period. During the dry season, the concentrations of DM, NDF, ADF and TC in the forage increased, while the CP, MM and NFC decreased. The principal component analysis showed that over 79% of the total variation was explained by the first two principal components for the structural characteristics of rangeland and animal performance. Herbage mass was negatively correlated with litter and positively correlated with rainfall. The higher the plant height, the lower was the percentage of bare soil. Sheep live weight had negative correlation with herbage allowance and stocking rate. We observed high species diversity (63 species and 25 families) with predominance of shrub-tree, and in most cases, species of low forage value. The botanical composition of rangeland showed higher presence of the following components: Malvaceaes (30.9%), “other species” (20.1%) and Cenchrus ciliaris L. (12.9%), which formed dissimilar groups. In the botanical composition of the sheep diet, via fecal samples by the micro histological technical, there was great participation of dicotyledonous, in average 59.6%. However, throughout selectivity index (SI) estimative, sheep selected more grasses during the rainy season (SI = 1.5) and dicotyledonous plants in the dry season (SI = 1.8). The Malvaceae was rejected (SI = 0.3) by sheep. In general, the Caatinga showed variation of herbage mass, botanical composition, chemical composition, animal performance and selectivity, throughout the year. It is recommended a management that contributes for maintenance of desirable species, leading to the increase of the rangeland carrying capacity.