Attacking my dogs

Question
I have 2 dogs and 2 cats.  The cats are 5 years old (orphaned at 2 weeks old and had ever since), Shadow is a 4 year old lab and Sadie is a 1 year old lab.  They have lived well together other than the occasional growl, hiss or swat, but this morning the cats have actually attacked Sadie to where they chased her out of the home.  I brought them back in a half hour later and they did it to both of them again, why would this sudden change in behavior?  Prior to this happening the cats were snuggling together cleaning each other and meowing like crazy and then when Sadie came down stairs they attacked.

Answer
My guess is something happened that you are unaware of.  Cats are like elephants, they never forget a bad encounter and might never get over it.  Dogs you can kick in the face and they'll come running back to you with kisses a half hour later.  

The best solution is separate them for awhile and reintroduce them slowly.