Yes you can use it for this purpose but if you freeze some of it it'll make it keep a couple of months longer.
Nigel (who I have just rehomed) is recovering from a respiratory infection and is really underweight, his previous owner was supplementing his food intake with critical care and I am doing the same until he starts to gain weight. He loves it and I mix his probiotic into it too. I would therefore say it would be ok.
sorry, but where would one get critical care and probiotic please? i would like to have some just encase. 8
Esther x