condolences to you but it seems the horse had good innings so must have been well looked after,
however the death could have been caused by old age, or by fireworks or even a mixture of both, the only way you could find this out for sure is to have a post mortem done to check for heart problems, if the horse had a heart attack this will show up in the post mortem,
one thing i have learnt is also that fireworks and animals dont mix so i dont use fireworks , but even though i dont their are a lot of people in the area that do which causes death of my birds occasionally when they are not used to it, however i would say that as your horse was 27 years young that in his lifetime he would have whitnessed his fair share of fireworks enough that he would be used to them by now.. with old age comes weakening of the heart and it is possible that the firework made him jump and his heart may not have appreciated this
i would say all in all that the old age is more than likely the problem with him and so dont feel to bad upon yourself, but as precaution in the future i wouldnt recommend the use of fireworks near where animals are kept ....
if the horse has lost weight due to old age the chances are their were in lying problems that cant be visually seen... i am sorry for your loss but dont beat yourself up to much over the fireworks as with all old horses 27-28 is a very good life ..most die before then of old age...and the chances are it was his old age that killed him
katie