Substantial stall waste is generated from horses on softwood bedding. The methane potential (G(pot)) of horse manure and constructed mixtures of stall waste with softwood bedding was determined at 35 degrees C. G(por) of 68, 191 and 273 mL/g volatile solids (VS) were estimated for three separate batches of horse manure, indicating variability in the material. Cumulative energy production over 20-40 days ranged from 3.11 +/- 0.92 to 8.45 +/- 5.42 x 10(5) kJ/metric ton wet weight horse manure alone, and from 1.69 +/- 0.39 to 3.91 +/- 0.47 x 10(5) kJ/metric ton wet weight horse manure plus softwood stall bedding (mixed at a 1:1 ratio on a VS basis). Softwood bedding was barely degradable and diluted the energy production of the stall waste; however, it did not cause inhibition of methane production from manure. Manually separated used softwood bedding contained substantial methane potential. (C) 2012 Elsevier Ltd. All rights reserved.