Spay or Neuter 
Why,
What age,
and more ?'s
male american bobtail with facial shields and muscular adult body
young american bobtail male
Tiger Bob facial development in pictures...
young american bobtail male with developing facial shields
male american bobtail with facial shields and muscular adult body
young american bobtail male without facial shields
     I do recommend neuter at 6-8 months prior to male maturity to prevent spraying and marking of territory, to optimize male development characteristics, 
and to prevent aggressive tendencies.
The recognized "safe" thing to do is neuter by 6 months of age.
My earliest spraying male was at 9 months.
     I do recommend spaying at 4-6 months to prevent accidental pregnancy and to prevent female spraying and marking to attract males.  Also to 
prevent aggressiveness.
Females can come into first heat at 4 months old!   One of mine did! 
(hot summer brought on early first heat, per vet)
Females can be almost constantly in heat during the warm months.
And females do spray/mark when not spayed.
Spaying fixes this and more...
Wiley facial development in pictures...
9 weeks old Male American Bobtail with no facial shields
Male American Bobtail 9 months old with facial shields
Wiley at 9 months old with good facial development.
Wiley at 9 weeks old with no facial shields
development of male American Bobtail facial shields
Wiley at 9 months old with good facial development.
Young American Bobtail (Tiger-Bob) with no face shields 
Young Bob with no face shields 
Young Bob with developing face shields
Mature Bob with face shields and body muscle development
Mature Male American Bobtail (Tiger Bob) with face shields and body muscle development
I often get asked for my "opinion" on when should you 
Spay or Neuter...
So here it is.
Not before 4 months old as they are too tiny and accidents happen.
But before they are old enough to spray or reproduce see insights below.
Just do it!  
:o}
American Bobtail male with face shields
Adult male American Bobtail with facial shields and body characteristics
American Bobtail Male with adult facial shields
 and adult body characteristics.