My Cocker Spaniel is looking slightly fat?

My Cocker Spaniel has recently been looking slightly fat. We have been feeding him the same amount of food he has had ever since he was fully grown. His belly does not have bloat as there are no matching symptoms. One reason I thought could have caused it was due to the winter, in the summer our dog normally has his fur cut and he can get a lot more exercise during the summer as opposed to the winter when his fur is much longer and it is harder for us to take him for a long run over the park.He seems to be just fine as he has no pain or discomfort, although he has been pooping in the house recently which he very rarely does.Is there any other reason for why he could be looking slightly fatter?

If you have ruled out overfeeding, then there ARE other possibilities.He could be retaining fluids due to his organs not functioning properly. Defects in the heart, liver, kidneys or pancreas can ALL cause fluid retention in the body.Have a thorough exam done by your vet.