TIP: The best grasses for horses are those high in fibre and low in sugar, such as Timothy, Brown Top and Cocks foot.
Kikukyu and Yorkshire fog are low sugar types and ok in some moderation, but not ideal. In the case of Kikukyu ensure additional calcium is added to the diet due to the binding effect (of calcium) that this grass has.
Grasses that are exceptionally high in sugar and in particular when they are in fast growth mode are Rye and Clover. These are not safe for susceptible horses and ponies most of the year and require strict pasture management to avoid problems such as obesity, fizzy behaviour, colic or laminitis in your horse or pony.