  We argue that the increase of the ratio baryon/meson due to the presence of
strong colour fields and percolation in ultra-high energy hadronic collisions,
helps to explain some of the global features of ultra-high energy cosmic ray
cascades at E>10^18 eV and, in particular the observed excess in the number of
muons with respect to current models of hadronic interactions. A reasonable
agreement with the small value and slope of the average depth of shower maximum
Xmax vs shower energy -- as seen in data collected at the Pierre Auger
Observatory -- can be obtained with a fast increase of the p-Air production
cross-section compatible with the Froissart bound.
