Emergence of seedlings from cattle dung collected in different seasons from grasslands of the Flooding Pampa was analysed. The objective of this work was to find out (1) how high the proportion of seeds from exotic species in the seeds spread by cattle dung is, and (2) what the forage quality of the species spread through cattle dung is. Fresh dung was collected in late spring and late summer from three grasslands. Seedling emergence from dung was done in greenhouse conditions. Seedling number, forage quality and origin of the species were determined. We found 121 plant species growing in the grasslands. The number of species emerging from dung was 41. Twenty-four and 36 species emerged from dung collected in late spring and late summer, respectively. Nineteen species were common for both seasons. There were 5.33 ± 0.26 and 1.00 ± 0.15 (mean ± SE) native and exotic species, respectively, per dung sample (22.50 g dry weight) collected in late spring. From the dung collected in late summer emerged 7.70 ± 0.31 and 2.63 ± 0.18 native and exotic species per sample, respectively. Carex spp., Cyperus spp. and Juncus spp. (native species) were the most abundant (95%) in dung collected in late spring. In dung collected in late summer Cynodon dactylon (an exotic species) represented 76% and Carex spp., Cyperus spp. and Juncus spp. represented 9%. The most abundant species emerged from dung were of low forage quality and thus are considered weeds in crop fields. Seed propagation through cattle dung helps to explain the increment of exotic species in the Flooding Pampa grasslands under grazing. The results are relevant for the range managers who normally move the cows between stubble crop fields and grasslands, spreading through dung seeds of species of different origin and quality.