Abstract Lowering dietary crude protein levels is a nutritional strategy recognized to both decrease the use of high-impact feed ingredients and reduce nitrogen (N) excretion. Improved pig manure management practices can further mitigate the environmental impacts associated with pig production towards net-zero emissions. Anaerobic digestion (AD) is a promising technology for transforming pig manure into energy as biogas and into bio-based fertilizers (i.e., digestate from AD). However, little is known about the effects of pig manure N content on AD. Thus, this study aimed to evaluate the impact of pig manure N content on biogas production and digestate quality through the AD of manure from pigs fed low crude protein diets. Three pig manure N concentrations were tested: T1 = 5873, T2 = 5421, and T3 = 5149 total Kjeldahl nitrogen (TKN, mg/L). Throughout 5 sequential fed-batch cycles (25 ± 4 days/cycle), biogas production and its composition (CH4, CO2, and H2S) were measured, while raw manure and weekly digestate samples were analyzed for total solids (TS, %), volatile solids (VS, %), pH, chemical oxygen demand (COD, mg/L), TKN, and ammoniacal nitrogen (NH3-N, mg/L). In a temperature-controlled room (20 ± 1ºC), 6 digesters (3 treatments x 2 replicates) were operated as single-stage reactors to digest pig slurry (mixture of urine and feces, TS: 5.6%) inoculated with a liquid inoculum (TS: 2.3%) to improve manure-microbe interactions. Data were analyzed by ANOVA using PROC MIXED with repeated measures and comparison of means through the Tukey test (SAS software). In addition, both correlation and regression analyses were performed with R to evaluate the relationship among variables. Decreasing pig manure N content showed a tendency to reduce biogas (-20% in T3 vs T1; P = 0.0782) and methane (-22% in T3 vs T1; P = 0.0576) production per cycle, as shown in Table 1. Regarding biogas composition, CH4/biogas and CH4/CO2 decreased with N content (-3 and -4% in T3 vs T1; P ≤ 0.0082). There were strong positive correlations between the N content of pig manure and the amount of NH3-N (linear: r = 0.94, R2 = 0.88) and TKN (linear: r = 0.90, R2 = 0.81) present in the digestate at the end of each cycle. These results suggest that a reduction in pig manure N content reduces biogas production and its quality (ratio of CH4 to CO2). This latter variable is important for biogas efficiency; thus, reducing crude protein in pig diets may impair the production of biogas in AD. However, a decreased N content may cause less emissions into the environment, but when using the digestate as fertilizer, it may not entirely fulfill the N requirements of fast-growing crops for a given application rate.