Vet at FirstVet answers:
Carrots are not poisonous to dogs. Carrots contain a substantial amount of fibre; some dogs can react to this by either developing diarrhoea or constipation if given too many carrots in one sitting. If you want to feed your dog carrots it is best to start with a small amount, and if tolerated, can gradually increase the amount given. Please bear in mind that carrots should be fed as a treat or be complimentary to the dog’s main diet (dog food).