The bone marrow of young pigs has a higher water content than adult bone marrow and, as expected, Peyman and Gabriel found that it has a higher conductivity. A little math might help understand why a higher water content in tissues this leads to higher SARs. Start with the basic equation for calculating the SAR:
SAR = σ E2 / ρ
where σ = conductivity of the tissue; E = electric field, ρ = density of the tissue
More simply, this means that the SAR is proportional to the conductivity:
SAR ∝ σ
and therefore as the conductivity increases, so does the SAR.