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Extension > Agriculture > Livestock > Horse > Nutrition and forages > Nonstructrual carbohydrate content of weeds commonly found in midwestern horse dry lots

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Nonstructrual carbohydrate content of weeds commonly found in midwestern horse dry lots

Danielle Gunder, University of Minnesota; Julia Wilson, DVM, Turner Wilson Equine Consulting; and Krishona Martinson, PhD, University of Minnesota

This project was sponsored by a grant from the Minnesota Horse Council.

Laminitis (or founder) is a devastating, painful condition for horses leading to losses in performance, increased veterinary costs, and even death. Diets high in nonstructural carbohydrates are a known trigger for laminitis. Horses that are easy keepers, or overweight, are also at a greater risk of developing laminitis and tend to be classified as having equine metabolic syndrome. Some of the most effective management tools for these horses are to limit their nonstructural carbohydrate intake by testing forage for nonstructural carbohydrate content, restricting amounts of feed to encourage weight loss, and confining to dry lots (i.e. dirt paddocks) in order to avoid access to pasture grasses that are commonly high in nonstructural carbohydrates.

Recently, researchers have recommended a total diet (i.e. hay, grain, supplements, treats) of less than 12% nonstructural carbohydrates for horses diagnosed with laminitis or equine metabolic syndrome. However, recent reports from horse owners indicate horses housed on dry lots are still experiencing recurring bouts of laminitis, despite being fed a low nonstructural carbohydrate diet. We believe that weeds that commonly grow in dry lots may be both palatable to horses and high in nonstructural carbohydrates; therefore, capable of triggering a laminitis episode. The objective of this research was to determine nonstructural carbohydrate content of weeds commonly found in dry lots housing horses or ponies with a history of laminitis.

During the summer of 2013, 10 horse farms in Minnesota and Wisconsin were visited three times (spring, summer and fall), and up to four weeds growing in dry lots housing laminitic horses or ponies were collected. Samples were sent to a forage testing laboratory and analyzed.

Twenty-seven different weed species were collected. The 6 most common weed species included prostrate knotweed, plantain, redroot pigweed, common ragweed, cinquefoil, and purslane (See gallery). The average nonstructural carbohydrate content of the weed species were different with plantain resulting in the greatest amount, and prostrate knotweed resulting in the lowest amount of nonstructural carbohydrates (Table 1). There were no differences in nonstructural carbohydrate content within weed species across farms; however, nonstructural carbohydrate content was higher during the fall (final visit). It is common for plants to have higher nonstructural carbohydrate contents in the fall due to weather. Most plants continually produce nonstructural carbohydrates during the day and utilize them at night. However, plants essential shut down during cool nights and therefore do not utilize nonstructural carbohydrates which contribute to higher levels commonly observed in the fall.

The average nonstructural carbohydrate content of plantain, cinquefoil and ragweed was greater than the maximum 12% total diet recommendation for horses diagnosed with laminitis or equine metabolic syndrome. However, the maximum amount of nonstructural carbohydrate content exceeded this recommendation for all weed species. Nutritive analysis of other components indicated the weeds would be palatable to most horses, especially ones housed in a dry lot on a restricted diet (i.e. horses who might feel hungry). All weed species were relatively low in structural carbohydrate components and high in crude protein. Combined, these results have proven to increase palatability; therefore, it is not surprising the horses consume the weeds.

Although this research did not directly link the ingestion of weeds to laminitis, the wide range of nonstructural carbohydrate content within the weed species suggests horse owners should control weeds in dry lots, especially if used to house laminitic horses and ponies.

Weeds photo gallery











All photographs compliments of University of Minnesota Stand Memorial Herbarium

Table 1. Average, maximum and minimum nonstructural carbohydrate content of six weed species commonly found in Midwest dry lots.

Weed species Nonstructural carbohydrate
Average Maximum Minimum
% Dry Matter
Plantain 16 30 4
Cinquefoil 14 21 11
Ragweed 12 16 4
Purslane 11 14 7
Redroot Pigweed 11 15 8
Prostate Knotweed 9 20 4
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