The High Heating Value (HHV) for beef cattle manure starts at approximately 8,500 BTU/lb for ash-free, dry manure. It then should be reduced by the ash and moisture content of the manure. Assuming 15% of dry solids is ash (85% combustible solids) and 60% moisture content (or 40% solids content), the HHV could be adjusted as follows:
8,500 x 0.85 x 0.4 = 2,890 BTU/lb of manure (Higher Heating Value)
If the solids are dried by the sun to a moisture content of about 25%, then the resulting solids will have an HHV of
8,500 x 0.85 x 0.75 = 5,420 BTU/lb
All manure analysis will provide the moisture content of manure, and some provide the ash content (you may need to ask specifically for this value) when sampling manure. Ash exists in manure as minerals and can be added to manure by sand bedding, soil, or other contaminants. Ash is the fraction of an organic material that does not burn.
Finally, the Higher Heating Value of any fuel assumes that the water produced by combustion of the hydrogen in the fuel and/or evaporated during the combustion process will be condensed and the energy will be recovered from that condensation process. This does not happen with most energy-conversion processes. So we prefer to use the Lower Heating Value (LHV) for fuels. LHV values for livestock biomass (manure, compost, separated solids) are not widely reported, but most biomass sources have an LHV that is about 90 to 95% of HHV. The separated solids at 60% moisture are likely to have an LHV below 2,500 BTU/lb. It is therefore to your advantage to harvest some sunlight and dry the separated solids as much as possible.