Lets go on the assumption that he IS tying up at the moment, as I am going to give a different diet a go and if no help then will involve vets etc. I also think a new diet may benefit him apart from the tying up issue. I've always been bad at nutrition stuff, but been doing some research.
I'm thinking of switching him over to a combination of Speedi-Beet as good roughage, CoolStance Copra to make it taste better, plus it has a lot of oils to give him energy and improve coat/hooves, adding Equivit Preserve Which is a supplement containing Vit E, Selenium and Magnesium, as well as Chaff and Hay.
I was reading that the CoolStance Copra is very high in protein, and Speedi-Beet ios lower, so the Speedi-Beet would balance it out as opposed to feeing just the CoolStance.
I'm not sure what chaff... I'm thinking Oaten or Wheaten. He is on Lucerne hay at the moment but I am trying to convince dad to switch to Meadow, but that won't be for 6 months at least.