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Monday, March 30, 2015

Weeds Commonly Found in Drylots

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 horses prone to laminitis 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 and digestible energy (i.e. calories).   

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. 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, conducted at the Univ. of Minn., 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 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. The average nonstructural carbohydrate content of the weed species varied with plantain have the highest and prostrate knotweed the lowest. There were no differences in nonstructural carbohydrate content within weed species across farms; however, nonstructural carbohydrate content was higher during the fall. It is common for plants to have higher nonstructural carbohydrate contents in the fall due to weather conditions. 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 consumed 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.  

This project was sponsored by a grant from the Minnesota Horse Council. Authors: D. Gunder and K. Martinson, PhD, Univ. of Minn. and J. Wilson, DVM, MN Board of Vet Med.


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