In Uruguay, different pig production systems coexist: confinement systems and pastoral systems. These systems differ in terms of production costs, animal welfare and environmental impacts. On the other hand, droughts caused by the phenomenon “La Niña” can change the normal behavior of pastoral systems. In this article we analyze the dynamics of nutrients and their potential environmental impact of two growing cycles of pigs in an outdoor pastoral system. Animals were housed permanently in an area with a shelter, feeders and drinkers. They also could enter in several grazing areas, although each grazing area was used only during one week. Most of the nutrients coming from animal manure accumulate in the area surrounding the shelter and feeding areas, but the increase of concentrations was lower in the grazing area. A slight increase of nutrients in the grazing plots was found between the access to a grazing area and its closing one week later. After closure, nutrient concentration declined with time. The same tendency was found with ammonia emissions. In the conditions of this study, the reduced rainfall resulted in a low loss of nutrients. We conclude that in the pastoral system, due to the low nutrient concentrations in the grazing area, no large-scale environmental risks can be expected. The permanent area, however, may have environmental risks associated to nutrient deposition. Some design changes could reduce the risk of loss of nutrients from the area of permanent closure of animals.