The Brazilian swine production has been grown 38.9% in the last decade. Inherent to the process, the pollution potential has increased which brings environmental concerns, especially about the final disposal of swine wastewater (SW). In this context, this work aimed to evaluate the responses of 'Piatã' grass (Urochloa brizantha, cv. BRS 'Piatã') to the fertilization with SW, with and without supplemental irrigation. The experiment was carried out for one year from March 2014 to March 2015. The experiment was conducted in a split-plot with a random blocks experimental design with four replications. The treatments in the plots were referred to the use of irrigation (with and without), and in the subplots to the SW doses (four doses: 75, 150, 225 and 300 m 3 ha -1 ). In the irrigated treatment, the irrigation was fulfilled to re-establish soil moisture in the field capacity (Ө fc ). The parameters used to verify the treatments were: total forage yield (TFY), leaves and stems yield (LSY), crude protein rate (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and in vitro dry matter digestibility (DivDM). There was a significant increasing effect for doses, reaching a mean TFY of 41.92 Mg ha -1 at the dose of 300 m 3 ha -1 . The combination of the highest dose of SW combined with supplemental irrigation produced the best results of TFY and LSY with (47.8 and 41.9 Mg ha -1 year -1 , respectively). Irrigation also led to the best results per cycle, with the highest forage accumulation in spring, 12.28 and 8.55 Mg ha -1 for irrigated and non-irrigated treatments, respectively. In the bromatological parameters, supplemental irrigation led to the highest average levels of CP, ADF and DivDM of 16.7%, 33.8% and 66.5%, respectively. The NDF did not respond to irrigation and SW doses. The research allowed concluding that irrigation and SW fertigation brought quantitative and qualitative benefits to 'Piatã' grass production.