If your dog has undergone some form or surgery and therefore spent a little time at a veterinary clinic or animal hospital, you may find that when you do eventually bring them home any other pets you have will react aggressively towards them and vice versa. It is thought this is because your dog has a lot of different smells on them which include other people, animals, medicines and strong scented disinfectants routinely used to clean animal clinics. There may even be some traces of the anaesthetic clinging to your dog's coat for quite a long time which again can trigger an aggressive reaction in other pets you have in your home.
It is thought that other dogs or cats in the home might well react this way because they are scared of these strange odours which they do not associate with your dog. Taking one dog out of the home for any period of time no matter how temporary, will end up causing a disruption in an established hierarchy because the order of things change which the other pets take advantage of especially if it is the alpha dog that had the surgery.
Conflicts start when your dog gets home with all these strange odours on them and it's when other dogs turn on them. However, the conflicts never last that long and are relatively minor if the sickly dog's absence has only been for a brief period of time. If they have been out of the home for longer and this means longer than 2 weeks, then you may need to re-introduce your pet gradually back into the home. You also have to bear in mind that your sickly may well be the instigators of any aggressive behaviour if they are the alpha dog in the home.
A dog that has undergone any form of invasive surgery may be a little irritable when they return back to the family fold and to some extent this is to be expected. This type of behaviour could be due to the fact they are experiencing some form of physical discomfort or they might be emotionally upset by the whole episode they have had to go through.
You might want to keep your dog away from other pets for a while to allow them to get back on their feet and to feel more relaxed about everything which includes being around their house mates. You will have to gauge how things are going and when you think the time is right, let all your pets mingle together again. If things seem okay, you should not interfere in any way and this includes not petting any of your pets which may cause a bit of jealousy.
A lot of dogs will go through a period of depression following an invasive surgical procedure which is very much the same as it is with people. You may find they have trouble sleeping, are not so keen on their food and reluctant to be groomed. It is normal for your dog to not want to be as active and they might well just want to be left alone. You have to remember that their normal routine was turned upside down when they were admitted into an animal hospital or clinic where their sleep patterns and feeding routines were altered quite suddenly and dramatically. On top of this they were kept in a confined space which would not have gone down too well.
You shouldn't worry too much because it will take your dog a bit of time to re-adapt to their usual surroundings. However, if they remain down and off their food for too long, then you need to discuss what to do with your vet because something untoward may be going on. Along with depression, you may find your dog a little bit aggressive but this is usually more defensive than being nasty and will usually stop pretty quickly as they become more relaxed and happy to be home.
Your dog could become more demanding when they get home and this type of attention-seeking behaviour could be due to the fact they are feeling very insecure. However, it is better not to over do it and "spoil" your dog because you could regret it in the long run. An example being that if your dog has been neutered and then starts to ask for more attention and you constantly offer them a favourite treat, you could end up with a very overweight dog and lots of health issues associated with obesity to boot!
Dogs learn things very quickly and if by whining or whimpering they get your attention, they will soon do this as a matter of routine which is unwanted behaviour that has to be nipped in the bud. In short, it is best to avoid setting yourself up for a fall by spoiling your dog because they have had to undergo some form of surgery.
You may also find that your dog goes through a period of messing in the house rather than asking to go outside. This is often seen as your dog's way or re-establishing their territory and to help relieve any anxiety or stress they may be experiencing. However, it could also be because their bowels and bladder have been affected by the type of medication they received when they were hospitalised.
You should never tell your dog off for messing in the house when they have just come home after having been hospitalised. The best thing to do is clean the area they have messed on and deodorise it thoroughly, then not allow your dog back to that particular area of the house. If you cannot do this, then place their water and feed bowl in the offending spot which should act as a deterrent and stop them from doing their business in the same place again. It won't be long before your dog is back to their old selves and things are normal again. You just to show a little understanding and patience for as long as it takes for your dog to feel they are "home" again.