Puppy with diarrhea

Mojo is 4 1/2 months now. He was doing fine until around
xmas, I was changing him gradually over from Orijen
to Barking Heads kibble. Then he managed to eat some
horse poo and some of the chicken's food
a day or so later he had diarrhea - so did my older dog
(who also ate horse poo!) I put them on chicken/fish and
rice, Toffee got better in a couple of days but Mojo keeps
getting the runs again every time I start to reintroduce
his food. He's back on fish & rice today, I'm worried this
is going on too long, perhaps he wont be able to go back
on the kibble. Does anyone have advice on how to go with
this? I will take him to the vets next week but I'm betting
they'll try & sell me some tinned Hills.

Try and fast him for 24 hours and start again with some boiled chicken and long cooked rice and see if that makes a difference first..

I dont really want to fast him as he is only a pup, & a very hungry one at that! The chicken /fish & rice is what I'm doing, it works, his poops get
back to normal (almost anyway) but as soon as I reintroduce his dogfood
he gets the squits again. Today he'll stay on white fish & rice, tomorrow
prob chicken & rice/potato, maybe some boiled egg, then his poops will
return to normal - that is when I'm not sure what to do next, perhaps
there's a puppy food that's gentle for sensitive tummys I could try him on for a while? I'll see if I can find some tinned Lilly's or Barking heads puppy food, any other suggestions?

Some dogs can be allergic to chicken and rice. Mine certainly is so I feed fish and sweet potato. That might help and also give prokolin to help the tummy. You could try giving plain yogurt to help line the tum. Just small amounts to start with but more meals over the next day or two. Also just for awhile boil his drinking water.

Acute (short-term) small intestinal diarrhea can be managed by withholding food, but not water, for 24 to 48 hours. If diarrhea stops, small amounts of a bland, low-fat food are fed three to six times daily for a few days, with a gradual increase in the amount fed and a slow transition back to the pet’s normal diet. Special diets usually contain rice, which is more digestible than other grains.

Don’t give your dog over-the-counter diarrhea medications without first consulting a veterinarian. If your dog’s active, not dehydrated, and has been previously healthy, acute diarrhea can often be managed at home. If the diarrhea is accompanied by other symptoms such as depression, or it continues for more than a few days, take your dog to a veterinarian.

is Prokolin a probiotic? If it is I'll ask the vet if its ok. I have
been giving bio yogurt & he had fish & sweet potato this am.
My problem is not stopping the diarrhea its how to get him back on his food without it starting again.

Maybe try a grain free food and add some canned pumpkin.. also the wet food will help as it will give back the lost liquid from the diarrhoea..

There is a new thought now on not starving any dog whatever its age as it takes the stomach too much time to get used to food. So small meals of a bland type eg: fish and potato. Prokolin is a probiotic and can be got from the vets but cheaper from other places. I keep a tube now in my dogs drawer for use if I have problems with upset tums. Has a long shelf life.

I never fast, I will always feed something even if it's dollop of natural yogurt with some white fish mixed in fed several times a day. Never had a problem transitioning back to normal food either tbh. I have a tube of prokaolin in the cupboard but have never had to use it.
Have you considered the horse poo may just be coincidence perhaps the kibble didn't agree with him, go back to the original kibble he had before the squits. In view of the fact it keeps reappearing try adding a little kibble to the fish and rice mixture and see what happens.

well Mojo did a nice firm poop this morning - but it was full of something
like wool....I have now removed the sheepskin rug from the living room!!
I dont think that's what caused his problem but he's always hungry atm
& has started stealing & chewing, so the sooner I sort him out the better!