when i had my sheep inspection,i asked the animal health lady (wer in scotland) and she was sure we cud easily get a mobile slaughter but it would cost us more than going to abattoir. but if u include diesel to abattoir, then diesel to collect the carcuss, then it might work out even.
id def consider it cos im sure the sheep have to wait overnight at our abattoir (as did our pigs..arghh...i forgot to check and only found out after) unless we arrive before 7am. which then means loading the night before anyway cos of dark etc.