feeding puppy formula to adult dog

 I'm no expert on diet or anything, and I'm sure someone will have a better answer. However, as far as I'm aware there's different nutrition in adult and puppy food. How come it's not in adult formula?

The adult formula has rice in it which gives him digestive issues.  There are no carbs or grains in the puppy formula which is why he tolerates it so well.

 Have you tried Science Diet's ID? That worked for my dogs in the past when they were having digestive issues.

In general, puppy formulas are higher in fat and protein than an adult formula.  This is actually beneficial for a toy breed, whose metabolism is higher than that of a medium to large breed.  My thought is that this is fine to feed to your Manchester Terrier.  For example, California Natural (I'm using the kibble as an example) makes an adult and a puppy formula--the adult formula is something like 21% protein and 11% fat which in my opinion is a bit low, wheras the puppy formula is 26% protein and 16% fat---more in line with most ALS foods.  I know many people with adult dogs with digestive issues that feed the puppy formula to their adult dogs with no ill effects.

Not knowing what the actual food is and checking all the nutrient levels, I cannot guarantee that it is okay to feed, but I would venture a guess and say that it is.

It needs to be remembered that puppy food can either be promoted as a puppy food or an all life stages food. Going along this route, technically a puppy food can be nutritionally acceptable to an adult so long as the percentages of fat and protein are acceptable for the dog's needs.

That said, if he you need a low-ingredient, high quality, grain free food, there are those out there. There are many grain free foods available as canned food that are limited in ingredients and are high quality. I would try those long before trying a food available on a grocery store shelf, as the quality of ingredients will be low, and the nutrition gained will be poor.