I have found that the value of net.netfilter.nf_conntrack_count variable change every time i reboot the system. Did any one have an explanation for that?  
Sysctl parameter change after every reboot
debian;systemd;sysctl
As one can lookup in Documentation/networking/nf_conntrack-sysctl.txt, this variable is not really a sysctl variable to tweak system behavior, but to read-only variable telling you something about kernel state, in this case:nf_conntrack_count - INTEGER (read-only)     Number of currently allocated flow entries.This number changes over time, since the number of allocated flow entries (connections, the conntrack subsystem is tracking at the moment) changes.  You could try it out by establishing a bunch of connections to some server and look how the value changes.