1. Introduction
The exact mechanism of reduction of fertilizing ability
of cryopreserved spermatozoa is not yet completely
understood. However, there have been studies on the
role of reactive oxygen species (ROS) in the functioning
of spermatozoa and their fertilizing ability after
liquid storage and cryopreservation [1–5]. Many studies
have shown that the main reason for abnormal
sperm functioning is lipid peroxidation (LPO) and antioxidant
imbalance, caused by the occurrence of oxidative
stress [6–9].
Oxidative stress occurring in the sperm is a phenomenon
associated with increased rate of oxidation of
cellular components and excessive production of ROS
[6,10]. Low intensity of oxidative stress may have beneficial
effects on cells [11], while its high levels can
cause destruction of nucleic acids, proteins, lipids and
carbohydrates, ultimately leading to the cell death [12–
15]. Effect of oxidative stress is particularly important
during the storage of sperm and its cryopreservation.
Chatterjee and Gagnon [2] and Park, et al [13] found
increased production of ROS in the process of freezingthawing
of semen. The main sites of its formation are
mitochondria [16] and sperm cell membranes [12],
which are particularly vulnerable to damage from sudden
temperature changes. An aerobic cell contains substrates
and enzymes to prevent or restrict the formation
and propagation of ROS, but the antioxidant defenses
of spermatozoa are relatively weak and these germ cells
are very susceptible to oxidative stress [9].
Our previous study [17] clearly demonstrated that
cryopreservation of chicken semen significantly enhanced
lipid peroxidation in live spermatozoa. We hypothesized
that susceptibility of fowl sperm to LPO was
caused by reduced antioxidants, or its diminished scavenging
activity, therefore the first aim of the present
study was to determine lipid peroxidation and antioxidant
enzymes activities in chicken spermatozoa before
and after cryopreservation. We also investigated the
effect of freezing-thawing on fowl semen parameters