  The $T$-dependence (2- 400 K) of the electron paramagnetic resonance (EPR),
magnetic susceptibility, $\chi (T)$, and specific heat, $C_{v}(T)$, of the
$normal$ antiferromagnetic (AFM) spinel ZnCr$_{2}$O$_{4}$ and the spin-glass
(SG) Zn$_{1-x}$Cd$_{x}$Cr$_{2}$O$_{4}$ ($x=0.05,0.10$) is reported. These
systems behave as a strongly frustrated AFM and SG with $% T_{N}$ $ \approx
T_{G}\approx 12$ K and -400 K $\gtrsim \Theta_{CW}\gtrsim -500$ K. At high-$T$
the EPR intensity follows the $\chi (T)$ and the $g$-value is $T$-independent.
The linewidth broadens as the temperature is lowered, suggesting the existence
of short range AFM correlations in the paramagnetic phase. For
ZnCr$_{2}$O$_{4}$ the EPR intensity and $\chi (T)$ decreases below 90 K and 50
K, respectively. These results are discussed in terms of nearest-neighbor
Cr$^{3+}$ (S $=3/2$%) spin-coupled pairs with an exchange coupling of $| J/k|
\approx $ 50 K. The appearance of small resonance modes for $T\lesssim 17$ K,
the observation of a sharp drop in $\chi (T)$ and a strong peak in $C_{v}(T)$
at $T_{N}=12$ K confirms, as previously reported, the existence of long range
AFM correlations in the low-$T$ phase. A comparison with recent neutron
diffraction experiments that found a near dispersionless excitation at 4.5 meV
for $T\lesssim T_{N}$ and a continuous gapless spectrum for $T\gtrsim T_{N}$,
is also given.
