Food choice for austrailian shephard

Question
I HAVE A AUSTRALIAN SHEPARD THAT IS 9 WEEKS OLD.  I HAVE NOTICED THAT HIS BEHAVIOR HAS CHANGED.  WHEN I GOT THE DOG, HE WAS EATING PUPPY CHOW AND I CHANGED HIS DIET TO THE SCIENCE DIET ABOUT A WEEK AGO.  SINCE THEN, HE HAS BEEN LOSING WEIGHT AND HE VOMITED ONE TIME ON YESTERDAY.  WHAT IS RECOMMENDED FOR ME TO DO TO?

Answer
Hello
Jeffrey;
The Science Diet is the begtger of those two foods.
The problem is not the change of diet, but the way the change is made.
When yopu switch a dog from ne food to another, you have to do it gradually, so as not to upset their digestive system.
In some dogs it will be a slight upset, in others, more severe.
You mix one part the new food with one part food they are eating, fo each feeding, for one week.
Then mix 2 parts new food to one part old food for one week. Then you feed all the new food.
That changes their system from one food to the other gradually.
He is probably losing weight, because he has probably vomited more then you have sen or he has had diarreah.
changing foods all at one like that can either make them vonmit and/or give them diarreah or constipate them.
Any of those things are possible, or all at the same time, when their dogestive system is upset.
Charlotte