Autovacuum is not running or working
We finally found the problem!! This database had a Standby Read-Only database but We broked the replication, removed all Standby parameters but We forgot to remove the  replication slot.
Yestarday we tried to remove the replication slot but We couldn't  because the database was not in standby mode:

zabbix_db=# select pg_drop_replication_slot('standby2');
ERROR:  replication slots can only be used if wal_level &gt;= archive


We had to 


Shutdown the database, 
Change wal_level to archive Startup 
Run again the pg_drop_replication (now it works) 
Shudown 
Disable wal_level 
Startup


And.. the autovacuum comes back!!

postgres 19381 19089  1 13:07 ?        00:09:59 postgres: autovacuum worker process   zabbix_db
postgres 19411 19089  2 13:07 ?        00:11:20 postgres: autovacuum worker process   zabbix_db
postgres 19430 19089  1 13:07 ?        00:09:51 postgres: autovacuum worker process   zabbix_db