Same question. Is the pup 43 days old or have you had him 43 days? If it is a puppy, you should take it into the Vet for an examination and they Vet will put you on a vaccination schedule and you need to make sure to follow that until the entire course of vaccines have been given. Not sure what area you live in but it is very important to get Parvo and Distemper vacs. One shot does not mean a dog is immunized.
As for food, a good dry *puppy* kibble should be all you need.
Congratulations on your new companion! Do you mean that the dog is 43 days old or that you've had him with you for 43 days? Vaccination needs depend on his age and whether he's already had a round of shots or not. His age also determines food requirements as they differ for puppies, adult dogs and senior dogs.
Find a veterinarian quickly so that you get started with the correct food and care advice for your dog in particular. While there are general guidelines to follow, some breeds have special dietary and grooming needs. It's very important to establish a solid relationship with a veterinarian. Our pets get sick from time to time and need medical care just as much as humans do. Should you ever have an emergency, things will go far more smoothly if you are a well-known client with a vet clinic. Make some phone calls and get pricing information for vaccinations. Not all clinics are created equally and prices can vary wildly. The most expensive clinics don't always provide the best level of care, so don't automatically discount the cheaper clinics.
If you've never owned a dog before, buy some books on proper dog care and training. If you can't afford to buy books, check some out at your local library. While you're at it, see if your library has DVDs about training and care. There are a couple of great TV shows on the air about dog training and psychology that can also help you. The National Geographic Channel airs "The Dog Whisperer" - most episodes on Friday evenings. Cesar Millan teaches people how to better communicate with their dogs to solve problem behavior. The Animal Planet Channel features Victoria Stilwell on "It's Me or the Dog." Her approach is also psychological in nature. There is much to be learned from both of them.
Please stay in touch and tell us more about your new friend!