DPS SPEC (Growl off)
#showtooltip !Spiked Collar
/petautocastoff Growl
/script SetSpecialization(1,2)

Tank SPEC (Growl on)
#showtooltip !Last Stand
/petautocaston Growl
/script SetSpecialization(2,2)

the first number in the "SetSpec.." is your pet's spec (1=fero; 2=tenacity; 3=Cunning)
the Second number is your hunter's spec (1=primary; 2=secondary)