  We compute the next-to-leading order virtual corrections to the partonic
cross-section of the process $gg\to ZH$, in the high-energy and large-$m_t$
limits. We use Pad\'e approximants to increase the radius of convergence of the
high-energy expansion in $m_t^2/s$, $m_t^2/t$ and $m_t^2/u$ and show that
precise results can be obtained down to energies which are fairly close to the
top quark pair threshold. We present results both for the form factors and the
next-to-leading order virtual cross-section.
