  Recently, two photons with energy of about 1 PeV have been detected by LHAASO
from the Crab nebula, opening an ultra-high energy window for studying the
pulsar wind nebulae (PWNe). Remarkably, the LHAASO spectrum at the
highest-energy end shows a possible hardening, which could indicate the
presence of a new component. A two-component scenario with a main electron
component and a secondary proton component has been proposed to explain the
whole spectrum of the Crab Nebula, requiring a proton energy of
$10^{46}-10^{47}{\rm ergs}$ remaining in the present Crab Nebula. In this
paper, we study the energy content of relativistic protons in pulsar winds with
the LHAASO data of the Crab Nebula, considering the effect of diffusive escape
of relativistic protons. Depending on the extent of the escape of relativistic
protons, the total energy of protons lost in the pulsar wind could be 10-100
times larger than that remaining in the nebula presently. We find that the
current LHAASO data allows up to $(10-50)\%$ of the spindown energy of pulsars
being converted into relativistic protons. The escaping protons from PWNe could
make a considerable contribution to the cosmic-ray flux of 10-100 PeV. We also
discuss the leptonic scenario for the possible spectral hardening at PeV
energies.
