Equine Ownership

Dangers of Grazing Fall Pastures

Despite the mild fall temps, there are changes happening to pasture grasses, and some toxic leaves may be invading, too.

Hay should be introduced as nutritional values drop in the fields, and beware frost-damaged grasses which can be a hazard to horses with metabolic issues. (jdross75 - stock.adobe.com)

By: Kim Izzo | October 30, 2024

Listen to this Article

0:00

-:--

Playback Speed

you're listening to an article from horse canada.com. dangers of grazing fall pastures by: kim izzo. the milder temps that much of canada is experiencing this fall has made riding much more pleasant. there’s also been the added advantage of being able to bathe your horse prior to clipping without the need of heat lamps and coolers! but all this mild weather coupled with overnight temperature drops can cause unseen issues in your paddocks, fields and pastures that might affect your horse’s health. “frost-damaged pastures can have higher concentrations of non-structural carbohydrates (nsc), leading to an increase in the potential for founder and colic, especially for horses diagnosed with equine metabolic syndrome, laminitis, obesity, or cushings,” explains krishona martinson, extension horse specialist with the university of minnesota (um) in the college newsletter. advertisement scroll to continue with content this is due to warmer than normal daytime temperatures which allow fresh grass to sprout like it’s a second spring. what also happens is that the sugar levels in more mature growths of grass don’t drop as the temperatures cool down. according to equine nutritionist madeline boast, during the day this process in plant physiology is known as photosynthesis, where sugars are produced to be used as an energy source by the plant. overnight, instead of photosynthesis occurring, the plant will use the sugars in a process called respiration. but in colder temps the grass and plants hold onto the sugar, creating a horse health hazard. “the general recommendation is that horses should be kept off of pasture for seven days after a killing frost – a frost severe enough to end the growing season – has occurred,” boast writes on sister media site horse sport. “at this point the nutritional value of the plant will decrease.”. she adds that different species will lose nutritional value at varying rates; for example, alfalfa will lose nutritional value faster than most grasses, as they will lose their leaves. she also explains that once the plant has turned brown and is not actively producing sugars anymore, the pasture is reasonably safe. another danger to horses in the fall is maple leaf toxicity. “red blood cell damage has been shown to occur in horses ingesting 1.5 to 3 pounds of dried leaves per 1,000 pounds of bodyweight,” martinson explains. however, this threat is only viable with dried or wilted leaves, not fresh, green maple leaves. if you’re unsure if your horse is ill from maple leaves, look for symptoms that include depression, lethargy, weight loss and dark red or brown urine 24 hours post-ingestion. and yes, maple leaf toxicosis can be fatal. keep horses away from areas where fallen and wilted maple leaves are plentiful. she adds that dries leaves can be toxic for about four weeks, but “they are not generally believed to retain toxicity the following spring.”. other plants that are toxic include horsenettle, white snakeroot and a toxic fungus that can infect ryegrass. often horses wouldn’t eat such plants, but once the grass is dead, they turn to whatever is in the field. this is another reason to do some research and learn to recognize the various plants that pose a danger to ensure they are not in your pasture. poor overall pasture quality is also an issue this time of year as we head into winter. as grasses become mature, the level of digestible nutrients decreases, as does the caloric value. keeping track of body weight at this time of year can be tricky, as a fuzzy winter hair coat can hide condition loss. just like in spring, horse owners and stable managers need to consider forage quality and quantity between the seasons. “ideally, owners need to slowly transition horses from a pasture diet to one of dry hay in preparation for winter feeding,” martinson says in the article. “we do not recommend over-wintering horses on pasture due to plant damage from digging, pawing, and hoof traffic.”. hay, whether in round bales or in a feeder, is a safer way to keep your horses healthy and happy over the winter. &&>

The milder temps that much of Canada is experiencing this fall has made riding much more pleasant. There’s also been the added advantage of being able to bathe your horse prior to clipping without the need of heat lamps and coolers!

But all this mild weather coupled with overnight temperature drops can cause unseen issues in your paddocks, fields and pastures that might affect your horse’s health.

“Frost-damaged pastures can have higher concentrations of non-structural carbohydrates (NSC), leading to an increase in the potential for founder and colic, especially for horses diagnosed with Equine Metabolic Syndrome, laminitis, obesity, or Cushings,” explains Krishona Martinson, extension horse specialist with the University of Minnesota (UM) in the college newsletter.

Scroll to continue with content

This is due to warmer than normal daytime temperatures which allow fresh grass to sprout like it’s a second spring. What also happens is that the sugar levels in more mature growths of grass don’t drop as the temperatures cool down.

According to equine nutritionist Madeline Boast, during the day this process in plant physiology is known as photosynthesis, where sugars are produced to be used as an energy source by the plant. Overnight, instead of photosynthesis occurring, the plant will use the sugars in a process called respiration. But in colder temps the grass and plants hold onto the sugar, creating a horse health hazard.

“The general recommendation is that horses should be kept off of pasture for seven days after a killing frost – a frost severe enough to end the growing season – has occurred,” Boast writes on sister media site Horse Sport. “At this point the nutritional value of the plant will decrease.”

She adds that different species will lose nutritional value at varying rates; for example, alfalfa will lose nutritional value faster than most grasses, as they will lose their leaves. She also explains that once the plant has turned brown and is not actively producing sugars anymore, the pasture is reasonably safe.

Another danger to horses in the fall is maple leaf toxicity. “Red blood cell damage has been shown to occur in horses ingesting 1.5 to 3 pounds of dried leaves per 1,000 pounds of bodyweight,” Martinson explains. However, this threat is only viable with dried or wilted leaves, not fresh, green maple leaves.

If you’re unsure if your horse is ill from maple leaves, look for symptoms that include depression, lethargy, weight loss and dark red or brown urine 24 hours post-ingestion. And yes, maple leaf toxicosis can be fatal.

Keep horses away from areas where fallen and wilted maple leaves are plentiful. She adds that dries leaves can be toxic for about four weeks, but “they are not generally believed to retain toxicity the following spring.”

Other plants that are toxic include horsenettle, white snakeroot and a toxic fungus that can infect ryegrass. Often horses wouldn’t eat such plants, but once the grass is dead, they turn to whatever is in the field. This is another reason to do some research and learn to recognize the various plants that pose a danger to ensure they are not in your pasture.

Poor overall pasture quality is also an issue this time of year as we head into winter. As grasses become mature, the level of digestible nutrients decreases, as does the caloric value. Keeping track of body weight at this time of year can be tricky, as a fuzzy winter hair coat can hide condition loss.

Just like in spring, horse owners and stable managers need to consider forage quality and quantity between the seasons.

“Ideally, owners need to slowly transition horses from a pasture diet to one of dry hay in preparation for winter feeding,” Martinson says in the article. “We do not recommend over-wintering horses on pasture due to plant damage from digging, pawing, and hoof traffic.”

Hay, whether in round bales or in a feeder, is a safer way to keep your horses healthy and happy over the winter.