The first thing is: don’t panic! Having a high oxalate horse pasture isn’t the end of the world, and won’t make you a ‘bad’ owner.
It is worth bearing in mind that if horses have access to some high and some low oxalate grasses in their pasture they will often select more of the low oxalate species. A horse in a paddock of 50:50 high/low oxalate grass is very unlikely to be actually eating 50:50.
High oxalate grasses often have some benefits, too. They’re often tough and drought resistant, and survive under heavy grazing pressure where other grasses die. They can provide green pick, omega-3 oils and ground cover at times of the year when low oxalate grasses and legumes have not survived.
Common high oxalate grass species include:
Setaria sphacelata – Setaria
Cenchrus clandestinus – Kikuyu
Cenchrus ciliaris – Buffel grass
Urochloa mutica – Para grass
Urochloa decumbens – Signal grass
Digitaria eriantha – Pangola grass
Megathyrsus maximus subsp. pubiglumis – Green Panic
Megathyrsus maximus subsp. maximus – Guinea Grass
Urochloa humidicola – Humidicola.
The web is full of more fantastic keys and resources to help identify the grasses in your paddocks. Your local Department of Primary Industries/Agriculture and your local nursery are also often very helpful.
If your pastures contain high oxalate grasses there are a few simple principles horse owners need to understand to balance horse diets correctly. Ingested oxalates bind calcium molecules which means that some of the calcium your horse consumes is not available for the horse to absorb into the bloodstream. The amount of calcium bound is proportionate to the amount of oxalate in the gut. Therefore the higher the oxalate level of your grass, and the more grass your horse eats, the more oxalates will be present.
This can mean that all the available calcium in the diet is bound and a horse can develop a calcium deficiency EVEN THOUGH THE DIET PROVIDES 100% RDI for calcium.
There are four simple strategies that can be used to overcome this danger:
- Add extra calcium to the diet (RDI plus enough to bind all oxalates present) Australian research confirmed that a diet needs at least half the amount of elemental calcium compared to oxalates (i.e. calcium to oxalate ratio of 0.50 to 1).
- Provide low or no oxalate roughage as a proportion of the diet. Feeding lucerne hay (which has the added benefit of being high in calcium), rhodes grass hay or meadow hay before and after the calcium supplement is fed is a good way of achieving this. If your horse is stabled or yarded overnight, offer a low or no oxalate grass hay such as rhodes for free choice consumption (unless your horse is overweight).
- Feed calcium supplements when oxalate levels are lowest. In practice, this can be achieved by locking your horse off high oxalate grass for at least half an hour before giving a hard feed containing a calcium supplement. This is a good time to feed some lucerne or low oxalate grass hay to reduce the amount of pasture consumed. Keep the horse locked off high oxalate roughage for about another half an hour after eating the supplements as well, to allow the body time to absorb the calcium fed in the absence of oxalates.
- A very effective and affordable form of calcium supplement is calcium carbonate (also known as Ag Lime or Limestone). It contains a high percentage elemental calcium and is highly available in the gut (provided enough is fed to bind the oxalate molecules and leave some over for the horse’s private use). Many owners also choose to include some chelated calcium in a form which is not bound by oxalates. It is not necessary to feed only chelated calcium to manage horses successfully on high oxalate pastures.
Remember that is also important to balance calcium levels with the phosphorous and magnesium levels across the whole diet. Equine Vit&Min TropiCAL Blend and EVM TropiCAL-Pro takes the worry out of balancing the diet of horses grazing high oxalate pastures. Farmalogic Equine also offers a free diet analysis service to help horse owners calculate their supplementation requirements.