Understanding and managing summer grazing and pasture

Written by: Sharon Smith MSc SEBC(Reg.) IEng ACIWEM BSc(Hons)

Summer is here (at long last!) and we can almost watch the late-spring grass grow taller before our very eyes. Pasture can be the cheapest and most environmentally-friendly form of feed, but we horse owners can’t, and shouldn’t, manage it like livestock farmers. Cattle and sheep are often single-breed, and of similar age. Many breeds of horses, of all ages, sizes, backgrounds and needs, often share the same field. Cattle and sheep can’t physically graze down to soil level as horses can, and they have to spend hours a day motionless to regurgitate and chew cud. Horses only chew something once; moving on to the next plant after just one bite. 

Horse appetite seems to be satisfied by dry matter intake (bulk), rather than how many calories they eat. 

So, the stages of grass growth are definitely worth the effort to understand, whether you have the horses at livery or on your own property.  1) Grass needs 3 things in order to grow: light, warmth and nutrients (including water).

2) Leaves (which are sweet, soft and don’t offer much ‘chew’ to a horse) turn daylight in soluble carbohydrate (simple sugars) through a process called photosynthesis. Photosynthesis stops at sunset each day, but growth continues overnight (if it’s warm and damp enough) using up the previous day’s sugar store.

3) The soluble carbs are converted into structural carbohydrate – growing larger leaves firstly, which are low in fibre, then deeper roots and a flower stem. Grass is most nutritious (energy, protein, fibre, vitamins, minerals) to animals while growing the stem.

4) Once the stem reaches the right height it buds. Protein levels decline sharply. This is why silage is an early-cut, just before the flowering bud forms, to capture the high protein for meat and milk when the cut grass still has the whole summer to regrow for grazing. In an uncut/ungrazed plant, however, photosynthesis continues and sugars form starch in the developing seed/grain, just like in oats or wheat grain.

5) The grass sheds its seed. Seeds will use starch as energy for germination and first leaf growth. What remains of the parent plant is now low in starch and protein. The plant will start to die back, leaving behind the structure. During this process, any photosynthesized sugar from the leaves will now be stored in the base of the plant, to sprout again in spring. Alternatively, grass that has set seed can be cut for hay.

6) The soluble carbohydrate content of cut hay depends more on the prior weather, cutting, drying and storage conditions, than the species of plant. If the weather is still warm and soil moisture is sufficient, a second growth may extend the grazing season. But in a dry midsummer, or frosty autumn nights, any re-growth will be limited.

Horses are often kept on over-grazed pasture to below 2cm (1”) sward height.

This naturally stops horses and most ponies eating too much – even if they graze all day [1]. It can help with weight-loss. But it is low-fibre/high-calorie grass and the horse will feel hungry. The horse can also damage their front teeth on the soil. Grazing to soil level will kill many desirable species of native grass. Ryegrass survives close grazing, and trampling, and will spread. Docks and undesirable weeds will invade bare soil. There are further consequences of cultivating only short plants in pasture: the root system reflects the size of a plant above ground. Short roots makes the plant susceptible to drought, stunting growth, the soil more likely to become deprived of air, compacted under hooves, and become waterlogged. Useful soil microbes drown, or are lost to watercourses with any topsoil. Any dung will not be degraded quickly. Mud-fever and other skin problems become more likely.

Farmers try to graze livestock in longer grass. Through grazing and cutting, they maintain the growth phase, a high leaf-to-stem ratio, for maximum nutrition, weight gain or milk yield. If we use the same strategy for horses as for livestock we will likely get the same result: rapid weight gain. Leafy grass is sweet and doesn’t provide enough fibre, and the horse will eat too many calories while satisfying their appetite. If we have a field of diverse grass and never let it seed: by over-grazing, silage-making or topping, then only the likes of sweet perennial ryegrass (which spreads by ‘tillering’, as well as seeding) will remain. This is good for livestock, but not the majority of horses.

Deep-rooted, tall, mature grass and plants help with drainage, aeration, and soil stabilisation – reducing erosion. A deep root system in ‘living soil’ draws more minerals up into the plant above ground to be eaten. Healthy soil makes nutritionally healthy animals. However, remember that the leaves will still be producing sugar during the long days of late summer. The horse may satisfy their appetite for fibre on mature summer pasture, but are still likely to eat too many calories with that fibre when days are long and sunny, and become fat.

So are we doomed to always struggle with our horse’s weight? No. Natives evolved to gain weight in summer and lose it in winter. The problems happen when we over-feed, over-rug, and under-exercise during winter. What if you have a fat horse now, on a livery yard where your choice is ‘in’ or ‘out’ for your horse, on whatever there is? I’ve successfully managed and advised owners keeping horses long-term in this situation for weight loss and gain. There are no excuses for obesity, or starvation! You just put the horse where the calories are most accessible, or not. Healthy horses on 24 hour turnout will not lose weight on a sward taller than the width of a credit card (5cm) or above 2cm (thumb-width) for ponies! Overweight horses can be removed from pasture by lunchtime, to avoid the highest sugar load. Weigh 0.5%BW (eg 2.5kg for a 500kg horse) mature hay and steam it. Soaking hay in warm water in summer is not a good idea, as it reduces dry matter and encourages rapid bacteria growth, and valuable nutrients are also leached into the water that is ‘thrown away’ and lost [2]. Allow ad-lib access to steamed, clean straw for the duration of being ‘in’. Just before turnout at night, offer a large bucket feed (2 round scoops for a horse) of dampened straw chaff. The steamed forage and straw should satisfy their appetite for dry matter and the need to chew, and chaff will fill their stomach and prevent gorging on fresh pasture when first turned out. Remember to give half a scoop of chaff from this allowance 30 min before exercise, to reduce the risk of gastric ulcers.

If you have the choice, rather than turn out in a small area of extremely short, unproductive pasture, it is better to provide your horses with a large, artificially surfaced area and feed a known amount of steamed, field-dried, stemmy hay, which you’ve grown instead of over-grazing. These plants would have had the deepest roots and so have the potential to draw up the most minerals.

Cross-grazing, allowing cattle or sheep to graze before horses, is an option for large fields and few horses. Alternatively, strip-graze pasture using temporary fencing. Move only a couple of stakes of electric fence up into mature grass twice a day, according to what your horses need, and closely monitor their weight. Remember to move up a back fence to allow the grazed pasture to recover.

Whichever pasture setup you decide to use, leave unfertilised, ‘set aside’ margins, 5-10m wide, around grazing areas. Herbs and grasses in the margins will over-seed the grazed areas and maintain diversity, for free. UK pasture tends to lack copper, zinc and selenium. Organic livestock farmers sew chicory, which cannot withstand over-grazing but is deep-rooted and high in minerals - especially copper and zinc [3]. Plantains can also contribute higher levels of copper and selenium than grass.

To take this approach further, I believe we are on the cusp of a revolution in how we keep horses at pasture; which will be as good for the environment as it is for horses. This system is a hybrid of woodland grazing for biodiversity, and ‘silvopasture’ for ease of hay production. Hedgerows define boundaries. Then a grid of horse-safe trees (avoiding oak and sycamore) shelter the horses and shade grass from sunlight to reduce sugars. But there are other benefits: produce a cash-crop; improve soil health and drainage; reduce the need for stabling or rugs; avoid sunburn; improve air quality; reduce fly nuisance by encouraging predator species like birds; dietary diversity (hazel twigs, for example, contain high levels of copper and would not need to seed) and countering climate change [4].

In summary, good pasture management includes poo-picking, worm counts to minimise chemicals, and ragwort/weed removal. But also treat your soil and pasture as the incredible resource it is for horses and the environment… whether you are producing hay to steam, or aiming for healthy grazing.

References
[1] Harrison, R., & Murray, J. M. D. (2016). A preliminary study of grazing intakes of ponies with and without a history of laminitis. Livestock Science, 186, 2-5.
[2] Moore-Colyer, M. J., Taylor, J. L., & James, R. (2016). The effect of steaming and soaking on the respirable particle, bacteria, mould, and nutrient content in hay for horses. Journal of Equine Veterinary Science, 39, 62-68.
[3] Nwafor, I. C., Shale, K., & Achilonu, M. C. (2017). Chemical composition and nutritive benefits of chicory (Cichorium intybus) as an ideal complementary and/or alternative livestock feed supplement. The Scientific World Journal, 2017.
[4] McAdam, J. H., Short, I. J., & Hoppe, G. M. (2006, June). Opportunities for silvopastoral systems in Ireland. In Proceedings of an IUFRO 3.08 Conference, Galway Ireland, UK.