So why is GREEN grass harder work for the horse’s metabolism compared to mature, stalky, yellower grass?
Considerable emphasis is placed on the sugar content, but there is a list of far more important aspects of grass that are adversely affecting domestic horses, starting with Nitrogen.
GREEN grass is high in nitrogen in the form of nitrates. This is because
- Nitrogen is derived from the decay of organic material in soil and animal plant waste – hence is comparatively scarce in arid environments where soils largely lack organic matter.
- Chlorophyll gives grass and other plants its green colour. The central molecule of chlorophyll is magnesium which is surrounded by 4 nitrogen molecules. Dark green plants like lucerne/alfalfa, blue/green algae, parsley, kale, spinach are particularly high in chlorophyll.
- Nitrogen is essential for plants to grow. ‘Nitrate’ is the form of nitrogen most used by plants for growth and development. Grass absorbs nitrates through their roots and stores them in the bases of stems and shoots – lucerne/alfalfa also stores them in their leaves.
- Nitrate levels increase in the grass any time the weather conditions inhibit growth:- growing in the shade, cool night-time temperatures, frosts, droughts or consecutive cloudy days when there is no sunlight for photosynthesis
- Horses need some nitrogen in order to construct proteins and they obtain this from consuming plants. However horses have no requirement for the nitrate form and it needs to be excreted immediately so it doesn’t get converted to the highly toxic ammonia.
- One way nitrates are excreted is by latching on to important cations – preferably sodium but if not available (sodium is always low in grass) they attach to calcium and/or magnesium, thereby robbing the horse of these important minerals. Just one reason why adding salt to feeds helps so much.
- Excess nitrogen is also converted to urea in the liver so that it can be excreted with the urine. When the liver can’t keep up nitrogen converts to ammonia
- A common question we get asked is ‘Why is my horse peeing more than usual?’ Because he needs to excrete the urea produced by conversion of excess nitrogen to urea in the liver. The removal of excess nitrogen takes water – the horse drinks more and pees more – not necessary when living in low nitrogen environments where water is scarce!
- Have you ever noticed burnt patches where your horse has urinated? This is because of the high urea content in his urine. Dog urine has the same effect.
What can you do about it?
- Where possible leave the grass to mature before grazing. Think standing hay. You also need to take into account the metabolic state of the horses grazing it. For many access will still need to be carefully managed.
- Avoid adding to the nitrate load by feeding lucerne/alfalfa, fresh herbs, green/wet haylage
- It is best not to harrow too often. A couple of times a year is good, eg early spring. Avoid urea/nitrogen fertilisers
- Add salt to feeds rather than relying on salt licks (approx. 10gms per 100kgs)
- Add GrazeEzy which helps to offset high nitrogen intake
- If you cannot control access to green grass make sure they eat as much plain grass hay as possible every day. This reduces green grass intake and ensures fibre requirements are met.
The horse grazing this grass was 'grass-affected' - bucking, bunny-hopping and generally 'carrying on'!
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