My Puppy, Bichon Poo Has Started Losing Hair From His Neck To Mid. Back, But The Rest Is Still Curly & Healthy What's Wrong?

There are many possible reasons of hair loss in your dog. I can give you few reason. Final diagnosis will be made by your vet. The possible reasons of hair loss in dogs are

1. Hyperthyroidism and cushing's disease.
   
2. Allergy to diet, pollen, dust, chemicals etc.
3. Parasites
4. Infections like ringworms, sarcoptic mange etc.
5. Hair loss due to pregnancy and lactation
6. Stress

So take your dog to vet for the diagnosis and proper treatment.