MIL dog losing weight quite drastically... we are looking after him while she is on holiday

[pud1]

Not sure why I am posting tbh. Other than hoping you will tell me not to worry.
I have a 3yo boxer and MIL has his paternal half brother also 3yo. They are very happy together and are always happy to see each other. I would say that my dog is the more alpha though. This is never shown aggressively it’s more of a feeling you have when you watch them together.
MIL has been away for 11 days and is back Tuesday. Her dog stayed with us for 8 days and then was supposed to stay back at home with niece. Niece called today and said that she left him yesterday for an hour and he has scratched the wall near the front door and made a real mess of the plaster. She was planning on going out today but didn’t want to risk leaving him so I told her to bring him round. He has drastically lost weight in the 3 days she has had him. She assured me that she has been feeding him his usual diet of dry food with some tinned meat. I have no doubt that she has been doing. She is studying animal welfare and really loves him.
He has been on a course of steroid and Piriton for unexplained scratching. Could this weight loss be due to steroids. I have just fed him and he is eating fine. He is wagging his tail and getting up to his usual silly behaviour with my dog. He has always been thinner than my boy but I can see his hip bones and spine.
Do you think we need a trip to the vets. Or could it be just that he is missing my MIL and FIL

[Booboostwo]

It could be psychological but it is best to rule out a physical reason first, so i’d take him to the vets. If he is stressed with his owners away Adaptil and/or Zylkene can sometimes help.

[user1471465525]

Steroids usually cause weight gain not loss.If he is eating normally then yes a trip to the vets to rule anything serious out.

[FrangipaniBlue]

My dog loses weight to the point you can visibly see his hips and ribs when we go on holiday.

He eats his usual food, same exercise and is his usually happy self, it's pure separation anxiety.

He also gets diarrhoea the first few days we're back (but funnily not while we're actually away!)

[slipperywhensparticus]

My cats would food refuse when I was away...has he had a gippy belly? Maybe the plaster ran through him?