The symptoms of “big head” disease (Osteodystrophia fibrosa) are affected gait, poor performance and swelling of bones of the head. Big head is a calcium imbalance caused when horses graze exclusively on grasses containing high levels of oxalate; that locks up calcium making it unabsorbable by the horse’s intestine.

Many introduced grasses contain oxalate. Setaria’s (purple pigeon grass has about half the oxalate content of other setarias) and buffel grasses contain the highest levels of oxalate followed by kikuyu, pangola and panics.Grasses with lower or zero oxalate content are Rhodes, creeping bluegrass, couch, paspalum and many native grasses.

Mixing legumes (Lucerne, clover, medic) with any high-oxalate grass in a grass/legume pasture will help to correct a calcium imbalance, while feeding calcium is also effective.

Source: DPI & F Note - Pastures www.dpi.qld.gov.au