02/09/2026
OXALATE GRASSES ARE AN ENVIRONMENTAL IMPACT ON YOUR HORSE'S HEALTH.
Australia is well known for having paddocks dominated by oxalate grasses also known as tropical grasses but they also grow far south of the tropics. Oxalates are a HAZARD for your horse's bone health.
Buffel, Setaria, Paragrass, Kikuyu, Signal grass and Pangola are all oxalate grasses common in many horse paddocks across the country. If not managed they invade other grass species and before you know it you have a paddock full of unsuitable, unhealthy grazing for your horse that will COMPROMISE your horse's bone density.
The horse consists of MUCH bone so when there is not enough calcium in blood, blood robs it from bone to keep organs functioning. This is a disaster for the horse as bones are weakened and deformed. The most common side effect of grazing oxalates is BIG HEAD DISEASE which is caused by lack of calcium, poor calcium absorption and blocked calcium absorption. The horse's calcium to phosphorous ratio becomes dangerously low (Ca/P). The oxalates in the grasses bind to calcium during digestion which ultimately blocks the uptake of calcium to put it simply.
I can tell you that adding a high percentage calcium supplement and feeding lucerne hay but horse still predominately grazing oxalate paddock WILL NOT IMPROVE YOUR HORSE'S CALCIUM LEVEL ENOUGH. I have decades of data on retesting horses with big head disease and if they remain on oxalate grasses their calcium level only inceases slightly, their symptoms only improve slightly and the Ca/P ratio level also only increases slightly.
What to do? You need to rip it out unless you can section off the oxalate section and have other areas free of oxalates that horse can graze on. Then provide a high percentage calcium supplement that may need to be fed two or 3 times per daily in feed. Once removed from oxalate grazing and adding a high percentage calcium horses do recover although much more slowly in the older horse. SERIOUSLY..... it is the only solution that provides measurable outcomes for your horse's bone health. Every other solution is just tinkering around the edges.
Low Calcium and a low Ca/P ratio are synonymous. Symptoms may include: bighead disease, bone abnormalities, unexplained swellings and lameness, spurs, brittle bones, fractures developmental orthopaedic diseases, very serious condition in young horses and pregnant mares, dental problems, hoof issues, muscle stiffness reduced performance.
Your horse often does not get a choice on what he or she can graze on so to keep your horse working longer and in a state of good health do not forget that some grasses are just not suitable or safe for your horse.
Kerry Marsh BAgrSc
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