Well, we've never wanted the ashes back but we've had several pts both, as an emergency and planned, by Yorkshire Equine Crematorium and have had excellent service.
I have used the Pet Crematorium in Durham for my dog and horse and they were so kind in both cases. Although I wasnt present when my horse was collected a friend was and she said they were very careful whilst removing him. They provided all the assistance I needed and although cremation is quite expensive especially for larger horses it helped to know he had the end my lovely boy deserved. Sorry to hear you will soon have to make the awful decision soon but sometimes it is the kindest option.