Differences in biodegradability can affect the treatment of slurry before its use in spraying. The objective of this study was to evaluate the effect of the generation and physical–chemical characterization of swine and dairy cattle slurries on different biological treatment technologies. This research involved monthly sampling (number/composition) for 1 year of 24 swine farms (16%), cattle farms (38%), and mixed swine and cattle farms (46%). The results obtained showed differences in feeding (3 l water kg −1 food for cattle and 5 l water kg −1 food for swine) and assimilation (0.6 kg food kg −1 milk produced and 3 kg kg −1 weight gain), which may influence the generation of slurry (57 l animal −1 d −1 in cattle and 31 l animal −1 d −1 in swine) and its composition. In addition, the composition of swine slurry [23 g chemical oxygen demand (COD) l −1 , 3 g total nitrogen (TN) l −1 ] is significantly different ( P < 0.01) to cattle slurry (4 g COD l −1 , 0.3 g TN l −1 ). Finally, the composition and the S index applied to swine slurry [COD N −1 = 8, biological oxygen demand (BOD) 5 COD −1 = 0.3, S index > 0] and cattle slurry (COD N −1 = 16, BOD 5 COD −1 = 0.6, S index < 0) show a difference on the biodegradability of both slurries. Suitability of anaerobic and aerobic treatment was assessed based on the findings.