Needing stitches ??

Does this dog's incision need to be stitched back up or can it heal on its own being opened as is ?

Hello and thankyou for your question.  This is a judgement call for your vet, who has examined the patient, rather than something to ask of someone online who has no context.  Is this a spey wound that I'm looking at, or something else?  It appears that the muscle beneath the skin is exposed, so further intervention is higly likely needed; one concern might be that the muscle layer is exposed to infection and that if the muscle wall layer of sutures breaks down, then the intestines could even follow, leading to severe peritonitis.  If infection is present, there may also be some concern as to whether sutures would hold at this time.  Hopefully by now, your vet has assessed this wound as an emergency; what was the plan of action and how are things progressing?

It looks to me that the wound has been interfered with by the patient - and the sore skin round about may make further interference more likely, so infection could be a very real enemy.  There is a judgement call here, which could be influenced by all kinds of factors, including the ability to prevent further interference with the wound, to provide antibiotiosis, the state of the tissues and the depth of the disruption.  I would strongly advise being guided by your vet or, for a second opinion, to ask for the picture to be checked by a surgon.

(by surgeon, I mean specialist.  We are all sugeons!)