Over-grazing by horses results in so-called 'horse-sick' pastures, with poor-quality grasses, unproductive and harmful weeds, a high population of parasites and an unbalanced diet for the horse.
Less palatable grasses are left to seed in rough patches where the horses also dung and urinate, leaving an uneven sward. Tall, growing weeds will also colonise these areas.
If the pastures are continuously grazed with horses, this unevenness leads to severe deterioration of the quality of the grassland. Over time, the grazed areas lose nutrients, which suppresses the growth of more productive grasses and allows weeds to become established.
In some cases, excessive levels of clover may also develop, which can cause colic in horses. In addition, high molybdenum levels in clover can lock up the availability of copper and could cause copper deficiency, particularly in younger animals.
Over-grazing in a wet winter can exacerbate the problem as poaching can result in even more weed growth.
However, well-managed grassland will provide an even, leafy and palatable turf, free from harmful weeds, produce a balanced diet and will appear attractive to the eye.
One of the critical aspects of good grassland management for horses is to match the horse's fairly constant demand for grass with the extremely seasonal pattern of grass growth. Grass growth peaks in the spring and early summer, falls in mid-summer and increases again in the autumn, depending on the weather.
Teagasc equine specialists advise that there are three main ways of matching grass demand to grass growth.
The first is to top paddocks regularly, the second is to close off some paddocks for hay, haylage or silage, and the third option is to graze excess grass with cattle or sheep.
Many horse owners are tempted to restrict fertiliser use in the early spring in an attempt to prevent excessive grass production and lush pastures, which are often associated with problems such as laminitis.
Unfortunately, this tactic can aggravate the depletion of nutrients in the over-grazed grass. The roughs increase in size and the pasture often becomes infested with thistles, docks, buttercups, nettles and, later, ragwort. A huge amount of time and effort will be required to return this type of sward back to good condition.
Now is a good time to assess your soil quality and what needs to be done in the coming months to maintain top quality pasture for this year.
The first step is to take some soil samples and have them analysed at a laboratory. Soil analysis costs in the region of €1.25/ha/year and will be valid for five years. A standard soil test will detail the soil's pH, lime requirement, soil phosphorus (P), soil potassium (K) and soil magnesium (Mg), together with nutrient advice based on soil sample details and results.
A pH of 6.0-6.5 is recommended for horse paddocks. This is slightly above the recommended pH level for agricultural grassland, to reduce the risks of low calcium levels in the grass. However, it is difficult to give an exact relationship between soil calcium and the uptake into the grass.
Grass will still grow adequately at levels below pH 6.0, but poor-quality grass and some weed species will be more likely to establish.
Some soils have a naturally high lime status, but even grassland in limestone or chalk areas may sometimes require applications of lime. Beware of liming soils with high molybdenum. A soil test is necessary to know the pH and molybdenum levels.
There is much debate about how much nitrogen should be applied to horse paddocks because of questions about how it relates to bone development in young horses and, for this reason, many studs will not spread any artificial nitrogen on their land.
However, research has proven that protein is wrongly implicated as the chief source of Developmental Orthopaedic Disease (DOD) and the usual causes are excess in energy and/or mineral imbalances.
According to Teagasc, inadequate protein is much more of a problem as bone growth is slowed down (protein comprises 20pc of the bone matrix).
Heavy applications of nitrogen are wasteful and produce lush grass, which can cause digestive upsets if horses are suddenly turned onto it. Weight gain and laminitis are other problems, especially in ponies.
Nevertheless, moderate applications of nitrogen (N) are necessary to improve grassland production and maintain fertility so that the more palatable and productive species of grass can survive.
An application of 25-30kg N/ha (20-25 units per acre) is sufficient at any one time, as this will not give excessive increase in protein content.
Your soil test results will show the phosphorous (P) and potash (K) levels of the soil. P levels under three parts per million (ppm) and K levels under 75ppm are deficient. Soils that are continuously grazed with horses are more likely to be deficient in P, while K results are likely to be variable even within small areas.
Department of Agriculture nitrate regulations stipulate that the total amount of livestock manure applied to your land in a calendar year must not contain more than 170kg N/ha. However, this is generally not an issue as most holdings are under this figure.
The rules also state that the total quantity of fertiliser (organic and chemical/bagged combined) that is applied to the land must not be more than the crops' -- in this case grass -- needs.
The amount of livestock manure applied in any year to land on a holding, added to what your livestock directly deposit, must not contain more than 170kg N/ha.
For example, a horse over three years old produces 50kg N/year, a two-to-three-year-old produces 44kg N/ha, a one-to-two-year-old 36kg N/ha, a foal 25kg N/ha and a donkey or small pony 30kg N/ha.
Finally, you must never exceed the maximum rates of fertilisation, as outlined in tables 12-21 of the European Communities (Good Agricultural Practice for Protection of Waters) Regulations 2006.
For more information on grassland management and fertiliser application for horse pastures, contact the Teagasc equine specialist team of Norman Storey, Wendy Conlon, Declan McArdle or Ruth Fennell, or your local agricultural adviser.
We will return to the topic of grassland management in a future article, which will focus on the management of horses at grass.