Good for you for being a responsible pet owner and having your dog neutered.
Honestly, at 12 months, your dog still has some more growing to do, and I would not be cutting back on his food.
Nutro is a mid-grade food, as is Kirkland...nothing too special about either food.
For the same amount that you pay for Nutro you could feed Canidae, and for a few dollars more, Innova, or Wellness...or some of the grainless foods such as EVO or Orijen.
I would just keep an eye on his weight, and exercise him...and he should not get fat. All my dogs have been neutered and spayed and I've never had an overweight dog.
Gina