Overweight Labrador

Question
Hi there. I have a black Labrador retriever who is almost 6 months old and weighs 27 kilos. I have always been feeding him with Purina Pro Plan Puppy Sensitive Dry Food (chicken & rice flavour) following the dosage chart written on the food bag by the manufacturer. Ok, I would always give a beat more and some treats in between the 3 meals per day. He would do his poop 3-4 times per day, and it looked good (not too dry, not too lose). One month ago I swithed to Purina Pro Plan Puppy Robust Dry Food (chicken & rice flavour), which, as I have been told, is almost the same as Puppy Sensitive and increased his dosage to 450 grams per day. During the last months I noticed that his hair colour is not that shiny any more, and also he has been shedding a lot. He has also been scratching his self a lot. Therefore, I have started giving him one Omega3 Oil capsule per day, as I have been told that it is helpful for skin and hair. The problem is that at the beginning I noticed he cut down his poop to 2 times per day, and it looked very dry. Following my vet's advice, I added about 10ml of Tufalac into his food and also some water. I did this for 3 days and stopped. Now the problem is that his poop is very lose. Tell me what you think is happening. Also, the vet told me to cut down his food dosage to 250-300 grams per day so he can lose some weight. I have done this, but the dog seems to be hungry all the time. The vet told me to give him some rice and yoghurt mixed with his food at night meal. I am very confused because some say yoghurt is bad and others say that it is good for the dogs. Please tell me what you think I should do.
Thanks in advance for replying.

Answer
It is possible you have made too many changes too quickly.  If a dog is having trouble keeping anything down or continuing diarrhea try this out of the manual I have from a large, knowledgeable dog guide school.

Bland recovery diet for dogs.

3 parts cooked rice, one part boiled hamburger or chicken, or cottage cheese. I think you can substitute boiled potatoes for the rice. Once in an emergency, we bought a plain baked potato from Wendy's.

This is meant for short time settling a dog's digestive tract. It is not the complete and balanced diet they need long term. I have seen it work.

Once you have stablized his digestive system with the above, slowly introduce an adult food.  The regular Pro Plan chicken and rice would be good or the large breed version.  Feed about the 300 grams and nothing else.  After several weeks evaluate him and go back to the Omega 3 oil capsule if his coat isn't good.  

Labs often are very hungry.  I don't know there is a good solution.  Some people add canned green beans or pumpkin.  If you try that, avoid salt or spice.  I question the rice and yougurt.  They would add calories but upset the balanced diet.  Yogurt is very bad because it is high in calcium and excess calcium is very bad for large breed puppies.  

People try to apply human nutrition to dogs.  Unlike people, dogs being fed dog food, are already getting a very well balanced diet.  Adding the things we need to eat more of only ruins the balanced diet they are eating.