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Managing Horse Pasture During and After a Drought

Managing Horse Pasture During and After a Drought
By Laura Kenny
Much of Pennsylvania has been under drought conditions this summer. If you graze horses, you may be wondering how this impacts your pasture management.
If you are in a drought and your pastures are composed of cool-season grasses like orchardgrass, tall fescue, Kentucky bluegrass, etc., they may be dormant and brown right now. Don’t worry - they’re probably not dead! Dormancy allows plants to adapt to drought stress. The leaves may stop growing or even die, but the growing point and energy storage area at the base of the plant (the crown) is still alive. If your pasture grasses are well-established and have deep root systems, they will revive with some moisture and cooler weather. A new seeding, however, may not have the energy reserves to survive the drought.
If possible, it is best not to graze pastures during a drought or while they are dormant. The grass cannot recover from the leaf removal and regrow during drought and dormancy. Without leaves, the grass plant cannot capture enough sunlight for photosynthesis and regrowth. If the crown is grazed, precious energy stores needed for recovery are removed. Additionally, a thin stand of grass exposes bare ground, allowing opportunistic weed seeds to germinate and spread later in the year.
Horse Nutrition and Health
While this may seem counterintuitive, drought can cause cool-season pasture grasses to accumulate non-structural carbohydrates (NSC) like sugars and fructans. Before the leaves die, they continue to produce NSC via photosynthesis, however the plant cannot use up those NSC for growth without water. Therefore, the NSC accumulate until growth can resume.
During and right after a drought, NSC levels can be very high in these grasses and potentially dangerous for horses that cannot tolerate high NSC in their diets (conditions such as insulin resistance, Equine Metabolic Syndrome, laminitis/founder, etc). Even metabolically normal horses may have some digestive issues due to the rapid change in forage nutritional composition after a drought-breaking rain.
In addition, drought can cause some plants to accumulate nitrates. These are less of a concern to horses compared to cattle or other ruminants. However, if combined with high nitrates in drinking water and from other sources, then you could see toxicity symptoms like colic and diarrhea.
Lastly, toxic weeds may become more of a concern during drought because of the lack of other forage available. Weeds with deep tap roots will stay green longer than shallow-rooted forage grasses. Weeds may also accumulate NSC during a drought, and if there are any toxic components, they may become more concentrated with less water in the plant. If horses cannot be removed from pastures during drought, they should be supplemented with hay while turned out to reduce the likelihood of them eating weeds.
Best Management Practices
Most horse farm owners in Pennsylvania do not irrigate their pastures, but if you do, a light irrigation every few weeks will keep the grass plants alive. Keeping the grass green and growing would take a lot of water, so delivering just enough to keep the roots alive (about ½ inch) will help the plants recover when rain returns.
To give your pasture the best shot at drought recovery, keep your horses in dry lots if you have them available. If not, try to keep at least some of your pastures empty through the drought. They will recover faster after rain. You will need to feed hay to replace the fresh pasture forage in the diet.
When rain returns, continue to rest the pastures for a few weeks until they have recovered. Wait until grasses have greened up and reached 6-8 inches in height before grazing again. If possible, continue resting the most damaged pastures even longer. Avoid overgrazing. As long as pastures are growing again, apply some nitrogen (30-40 lb/acre) in the fall to stimulate root growth. If pastures do not recover after rain returns, you may need to reseed in the spring (typically March to May in PA). Use soil tests to make sure your pasture’s soil fertility is optimal prior to seeding.
To grow pastures that withstand drought longer in future years, consider a pasture management program that includes soil fertility testing, regular mowing, weed control, and rotational grazing . A grazing system that removes horses from pastures before plants are overgrazed, and gives them a chance to recover and regrow, will result in deeper roots that can access deep soil moisture. A shallow root system will become drought-stressed faster than a deep root system. In addition, a thick stand of grass shading the soil surface will help to keep it from drying out and weeds from germinating.
Many horse farms keep horses out on pasture during a drought, which damages the forage plants and delays recovery after the drought. Instead, horses should remain on dry lots, if available, during a drought. This practice, combined with good pasture management practices, will benefit the health of both horse and pasture.
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