Here are some basics about grass and pasture management that can really affect your horse’s health.
During the day grass uses sunlight to make sugars through photosynthesis. This means that the sugar content of grass rises during the day. These sugars are stored for growth, which happens later. Grass that really wants to grow will try to make more sugars, for example when grass has been grazed very short or with rainfall after a period of drought and stress.
At night, the grass uses the stored sugars to grow. Growth only happens at night and sugar production only happens when the sun’s out. To grow, the grass needs certain nutrients from the ground, it needs water and it needs the right temperatures. Grass doesn’t grow when it’s freezing, when the ground is too dry or when the nutrients have been depleted (for example when the pasture hasn’t been fertilized for too long). When the plant doesn’t grow as much at night, it doesn’t use up its sugars as much either, so the sugar content stays higher than usual until morning when the plant starts to make even more again. Normally, the sugar content in grass is lower in the morning than it is in the afternoon.
The other thing is that when grass is “stressed”, so when it doesn’t have enough nutrients to grow or it’s too dry to grow, the grass goes on survival mode. This means that the grass produces a higher proportion of fructans than it normally would. Fructans are a type of “simple sugars”, but they differ in the sense that horses can’t digest them well in the small intestine where sugars are usually digested. Because of this, most fructans end up in the hindgut undigested. The hindgut isn’t made to digest fructans either, so they disrupt the sugar-sensitive bacteria causing digestive problems and soft faeces or diarrhoea. Harmful substances are made and taken up in the blood, which causes issues like laminitis and founder. Research shows that when you give a horse too many fructans, even a healthy horse will get laminitis. The grass makes more fructans than other simple sugars during periods of stress because it’s their survival strategy. They can store hem better and longer, so they can use them to grow again when circumstances become more favourable. Stressed grass is therefore dangerous to a horse, especially if it’s prone to laminitis (obesity, PPID/Cushings, a history of laminitis, senior insulin resistance, Equine Metabolic Syndrome).
The grass takes up nutrients from the ground. It tries to take up enough of everything, but what the ground doesn’t have to give, the grass doesn’t get. The Manawatu area is known to have low Selenium, but also doesn’t contain enough trace minerals to keep every horse healthy. Nutrients such as Zinc, Copper, Manganese and such are anti-oxidants and play an important part in the horse’s immunity, keeping the body healthy and rejuvenising the body’s cells. Other nutrients, such as Phosphate, Calcium, Potassium, Iron, Magnesium, etcetera are also important to maintain the body’s structure and function. Pastures that are not tested for composition and not treated with the right fertilizer yearly to maintain the right nutrient composition will definitely have deficiencies. The wrong balance of certain nutrients will make uptake of certain other available nutrients more difficult. For example, too much potassium will obstruct uptake of magnesium. To give our horses enough of the nutrients they need to keep their bodies strong and in good health, we need to offer them another source of minerals besides grass.
When grass has grown longer its stems harden. Older, harder, longer grass contains more lignin (the woody substance that makes the stems hardier) which is less digestible. Long, fully grown grass doesn’t make as much sugar because it doesn’t need to grow much anymore, so it contains less sugars and fructans. Altogether, longer grass is less high-energy, and therefore safer. It also has more fibre, which adds to the horse’s gut health.
The horse gets its vitamins from different sources. Vitamin A mainly comes from grass (retinol, beta-caroteen). Vitamin B is produced by bacteria in the hindgut. Good hindgut health is therefore important. Vitamin C is produced by the liver. This sometimes doesn’t happen as well in older horses with bad liver function. Most senior feeds contain more vitamin C to compensate. Vitamin D is made by the skin under influence of sunlight. Some literature suggests that horses that are rugged for most time of the year, and dark coloured horses might not produce as much / enough. Vitamin E also comes from grass. When hay is fresh it contains vitamin E, but this steadily declines as hay is stored.
Every grass species has its own characteristics, or tendencies to make more or less sugars, have more or less lignin, have more or less protein, etc. Horses were made to eat long, stemmy (lignin), low-energy grasses. Dairy cows on the other hand, need a grass species that has high-energy, high-sugar, high protein content and less need for structure than a horse. Ryegrass is a typical dairy-cow grass species. Grass species that are ideal for horses have a 50% lower fructan content and more structure for hindgut health. Another important issue is that grass grows from the point where the leaves come out of the stem. When grass is grazed shorter than this point it takes much longer to regrow. Horses graze much closer to the ground than cows do, so grass for horses should have strong roots and leaves that start much closer to the ground. This helps your grass regrow faster, so that you don’t need as many paddocks or as much time to rotate your horses, the grass doesn’t get as stressed and weeds don’t get as much chance to grow. Pastures that are grazed too short risk weed growth. Horsy grass is also more resistant to treading and quick sprints. Horsy grass is denser, and therefore allows less opportunity for weeds to grow. And last but not least, horsy grass is less prone to endophytes, which cause grass staggers. For more information on where to get horse-type grass seeds, please contact Dr Lucy Waldron from LWT Animal Nutrition Ltd.
Over time, the ground slowly acidifies. Most pastures that are tested have a low pH. When this happens, the grass can’t take up nutrients as well and gets stressed, which we’ve established isn’t good. Best to treat such pastures with limestone or chalk to correct the pH of the ground. Best time to do this is autumn. That way, by the time the grass is ready to grow again in spring, the pH has corrected.
In other words, these situations can be dangerous for your horse:
Warm sunny days and cold nights: sugars have not been used up at night.
Unfertilized, nutrient depleted, short pastures: more fructans
Pastures with Ryegrass instead of horsy-grass
Rainfall after longer periods of drought: suddenly the grass can grow again and will start to produce lots of sugars again to facilitate that. The grass will be safer a week later.
Spring and autumn typically have days that combine some of these, so that grass can suddenly grow after a period of stress (winter or a dry summer), plus good sunny days and cold nights. This is why we sometimes get a flush of laminitis cases all at the same time in the area.
How should you maintain your pasture?
Re-sow entirely or if you can’t, sow over the existing grass at least every 10-15 years. Best time to do this is early autumn, or otherwise spring, when temperature and rainfall are favourable for grass growth. Try to put new grass seeds down on bald patches every year.
Take a ground sample to have analysed, so you know which nutrients are deficient and what the pH of your pasture is. Chose the right type of fertilizer to replenish the ground. Fertilize the grass 1-2x per year to make sure the grass has the nutrients to grow and won’t produce too much fructans. Nitrate is an essential nutrient for plants. Fertilizers or manure contains Nitrate in the form of ammonium. Bacteria in the ground transform this into Nitrate, which is taken up by the grass’ roots. Nitrate is necessary for grass growth. You can make use of artificial fertilizers or ask a farmer to spread out its effluent (cattle manure) on to your pasture. Effluent from cattle has a more slow-release Nitrate source than that of pigs, which means that the grass can make use of it over a longer period of time and there’s less leaching (washing out due to rain). Ask them to spread 10 m3 – 15 m3 of effluent per hectare, because more would contain too much potassium, which negative influences the uptake of magnesium and some other essential nutrients for horses. If you’re planning on using artificial fertilizers, there are different kinds on the market. They often contain a nitrate-phosphorus-potassium constituent. Regular products often release the nitrate in about 10 days, which means that the grass goes through a “growth spurt”, which means it suddenly makes a lot of sugars to facilitate that. This can be a risk for your horses, so either don’t graze your horses on the paddock until a few weeks later when the grass has matured or use a fertilizer that has a slow-release nitrate source (ENTEC, releases nitrate over 2-3 months). Phosphorus is important for young grass roots. It helps them utilize the nutrients from the ground better and keeps weeds and unfavourable grass species back. Phosphorus is also an important nutrient for the horse’s skeletal development. Magnesium is an important nutrient for grass and horses. Usually, magnesium in the ground is low and potassium is high, which further decreases the uptake of magnesium by the grass. Some fertilizers contain added magnesium as well.
Make sure your pasture isn’t grazed too short by rotating on time. By preventing the grass from being grazed too short, the plant doesn’t get stressed and doesn’t make too much fructans. Grass of about 15cm has grown a bit more, has a more balanced out nutrient content (if the ground allows it) and is appropriate for horses to graze on. Move them to a new paddock as soon as they have grazed the current one down (grass length 5-6cm). Rotate between 3-5 paddocks to allow for grazed down paddocks to be fertilized, maintained, rested and regrown to the right length. That way your horse will always get the right quality grass.
If your paddocks are drying out and grass is not growing well, prevent damage to your paddocks by rotating and feeding your horses extra hay so they don’t graze the paddocks too short. Remove faeces at least twice a week.
The quality of the grass is maintained by removing the faeces from the pasture at least twice a week (which also prevents worms from becoming a problem), preventing your paddocks from becoming too heavily stocked creating bald patches, rotating between pastures regularly and by letting the grass grow out and mowing it every now and then.
