CONICET | Buscador de Institutos y Recursos Humanos

The changes in forage availability and the physicochemical variability of plants influencethe diet selection by herbivores. In this study, the foraging behavior of Creole goats wasstudied in terms of botanical composition of the diet, food availability and physicochemi-cal properties of vegetation. The study was performed in a desert rangeland in the northeast(NE) Mendoza region in Argentina. Experiments with grazing goats were made in dry (win-ter) and wet (summer) seasons and cafeteria experiments (feeding trial) were performedduring the summer. Food availability was estimated from forage species cover. Botanicalcomposition of the goat?s diet was determined by microhistological analysis of fecal sam-ples. Morphological parts of forage species consumed by goats were sampled and analyzedto determine chemical traits (plant nutrients and secondary metabolites) in both seasons.Also, during summer, the two morphological traits of browse species stem specific den-sity (SSD) and specific leaf area (SLA) were evaluated. In the experiments with grazinggoats, diet selection was evaluated based on Ivlev?s electivity index (? I) and, in cafeteriaexperiments, preference was estimated based on the number of bites. Diet selection variedbetween the two seasons. Grazing goats showed differences in the patterns of diet selec-tion related to changes in forage availability. The botanical composition of the diet had agreater (p < 0.001) participation of woody species in relation to grass species in both sea-sons, but the herbaceous stratum was more utilized by goats during the summer accordingto their higher availability. Correlations between diet and availability were positive in bothseasons, but not significant in summer. The models including crude protein (CP), neutraldetergent fiber (NDF) and total phenols (TP) had substantial support for predicting varia-tion in diet selection in summer and winter. In both seasons the preference increased asthe concentrations of CP, NDF and TP increased, but the effect of CP was significant only inwinter. Thus, goats selected supplementary food mixtures (mixed diet) and tannins werenot considered dissuasive but, rather, were maintained below a certain threshold. In sum-mer, SSD was negatively and significantly related to diet selection by grazing goats. Thismorphological trait allowed explaining a greater percentage of the variation in?I (36%) withregard to the variation explained by the chemical variables (16%). In cafeteria experiments,in summer, the optimization of nutrient intake rate through consumption of species withlow SSD values represented a best explanation for the preferences observed, whereas thehypotheses of minimization of secondary metabolites and maximization of nutrients werenot able to fully explain the preferences observed in cafeteria experiments. To conclude,dietary decisions by goats in desert rangelands could be interpreted in terms of intake rateoptimization and complementation of nutrients and secondary compounds, rather than byexplanations involving the isolated effects of nutrient intake maximization or tannin intake minimization.