Investing in grass tissue tests to find out what nutrients are, or crucially are not, available to your horses is crucial.
Paying attention to the detailed management of your grass sward can help you produce healthy, happy animals.
Tissue testing grass in the spring to assess nutritional content
The tissue test above was taken from a Clay Loam soil that has a naturally high Magnesium content, and also a good background level of copper.
But you should never assume that what is in the soil will be available to your horses. The situation displayed in the above tissue test often happens after periods of high rainfall, and then drought – think back to the winters of 2018-2019 and 2019-2020.
Horse owners should all be aware of the problems Staggers, hypomagnesaemia or Grass Tetany, causes in horses when they are turned out on fresh grass in the spring.
In the plant, the uptake of magnesium is supressed in preference to taking up potassium. Because magnesium plays a key role in the function of the central nervous system, the animals are then prone to muscle tremors, staggering and collapse and / or poor appetite and reduced performance due to the rapid uptake of potassium.
In acute cases in older animals, or on low magnesium soil, grass tetany symptoms can occur in as little as three to four days.
But because magnesium is hygroscopic, its hydrated radius is much larger than normal during periods of high rainfall. Therefore, mass flow to plant available nutrition will be high.
Potassium is required in a plant to transport nutrients up the xylem tubes in the plant to sites of utilisation. In effect this means nutrients that are absorbed into the roots are moved to the growing points of the plants (leaves) and the immature seed sites. Hence the rapid uptake of potassium.
But this mass flow also results in significant volumes of magnesium leached out of the soil in the autumn and winter as a result of a high positive water balance. So, in the spring the soil will be largely denuded of magnesium.
Conversely, in periods of drought the transport of magnesium to the roots is significantly impaired. Hence the results of the tissue test detailing low available magnesium, and crucially copper.
Problems associated with flooding followed by a drought
The main issue is a compromised soil mineral delivery system due to damaged soil structure adversely affecting the roots ability to absorb nutrients from the soil.
One significant effect of this adverse weather is that Phosphorous is rendered unavailable causing a loss of fertility.
Also, grass can be low in zinc which adversely affects foot health and the renal system in ungulates.
Another significant problem (shown below) is that the plant absorbs abnormally high levels of molybdenum (irrespective of soil levels), or even Iron.
When horse graze on grass that is excessively high in molybdenum, the animals are unable to absorb copper. Copper, and zinc, are crucial for efficient renal function.
The low available copper and/or zinc will have a negative impact on manganese availability, which means that the horse has problems accessing energy from ingested food. Scouring and loss of condition and lethargy are a regular consequence.
What nutrients are, or are not – available to the horses
Just to remind you, the symptoms of copper deficiency in ungulates include changes in the coat structure and appearance, a loss of appetite and scouring.
In severe cases young animals can develop osteochondrosis resulting in bone fractures, or abnormal bone development.