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Translational animal science2020; 5(1); txaa224; doi: 10.1093/tas/txaa224

Evaluating digestibility and toxicity of native warm-season grasses for equines.

Abstract: Introduced cool-season grasses are dominant in Virginia's grasslands, but their high digestible energy and nonstructural carbohydrate (NSC) levels pose a risk for horses prone to obesity and laminitis. Native warm-season grasses (NWSGs) have lower digestible energy and NSC levels that may be more suitable for horses susceptible to laminitis. Although NWSGs have desirable characteristics, they are novel forages for horses. Little is known about NWSG intake or potential toxicity to horses or how grazing by horses may affect NWSG swards. The overall objectives of this research were to 1) assess voluntary intake, toxicological response, and apparent digestibility of NWSG hays fed to horses; and 2) evaluate the characteristics of three NWSG species under equine grazing. For the first objective, a hay feeding trial using indiangrass (IG) (Sorghastrum nutans) and big bluestem (BB) (Andropogon gerardii) was conducted with nine Thoroughbred geldings in a replicated 3 × 3 Latin square design. Voluntary dry matter intake of IG and BB hays by horses were 1.3% and 1.1% of BW/d, lower than orchardgrass (Dactylis glomerata), an introduced cool-season grass, at 1.7% of BW/d (P = 0.0020). Biomarkers for hepatotoxicity remained within acceptable ranges for all treatments. Apparent dry matter digestibility (DMD) did not differ among hays, ranging from 39% to 43%. NSC levels ranged from 4.4% to 5.4%, below maximum recommended concentrations for horses susceptible to laminitis. For the second objective, a grazing trial was conducted comparing IG, BB, and eastern gamagrass (EG) (Tripsacum dactyloides) yields, forage losses, changes in vegetative composition, and effects on equine bodyweight. Nine, 0.1-ha plots were seeded with one of the three native grass treatments, and each plot was grazed by one Thoroughbred gelding in two grazing bouts, one in July and another in September 2019. IG had the greatest available forage, at 4,340 kg/ha, compared with 3,590 kg/ha from BB (P < 0.0001). EG plots established poorly, and had only 650 kg/ha available forage during the experiment. Grazing reduced standing cover of native grasses in IG and BB treatments by about 30%. Horses lost 0.5-1.5 kg BW/d on all treatments. Findings suggest IG and BB merit further consideration as forages for horses susceptible to obesity and pasture-associated laminitis.
© The Author(s) 2020. Published by Oxford University Press on behalf of the American Society of Animal Science.
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Publication Date: 2020-12-03 PubMed ID: 33501415PubMed Central: PMC7810257DOI: 10.1093/tas/txaa224Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article investigates the suitability of native warm-season grasses (NWSGs) as a healthier alternative to cool-season grasses for horse diet, in particular for horses prone to obesity and laminitis. Two types of grasses, indiangrass (IG) and big bluestem (BB) were studied in terms of various parameters, such as toxicity, digestibility, and horses’ ability to graze on these grasses.

Objective 1: Hay Feeding Trial

  • The first part of the research involved a feeding trial where hay made of IG and BB was given to nine Thoroughbred geldings in a 3×3 replicated Latin square design.
  • Findings indicated that voluntary dry matter intake of IG and BB hays were 1.1-1.3% of the horse’s body weight per day, lower than cool-season grass like orchardgrass, which was ingested at a rate of 1.7%.
  • All biomarkers for liver toxicity remained within normal ranges for all types of hay, indicating that these types of grasses might not be toxic to horses.
  • The apparent dry matter digestibility (DMD) ranged from 39% to 43% for all hays, suggesting comparable digestion rates among different grass types.
  • Low non-structural carbohydrate (NSC) levels ranged from 4.4% to 5.4%. These levels are considered safe for horses prone to laminitis.

Objective 2: Grazing Trial

  • The second part was a grazing trial, where the researchers compared the forage yield, losses, and changes in the vegetative composition in IG, BB, and a third type of grass called Eastern gamagrass (EG) under horse-grazing circumstances.
  • The IG had the most available forage at around 4,340 kg per hectare, followed by BB with 3,590 kg per hectare. EG had significantly less, only 650 kg per hectare.
  • The grazing trials also revealed that horses’ grazing reduced the standing cover of native grasses in IG and BB treatments by about 30%.
  • Horses lost between 0.5-1.5 kg of body weight per day on all treatments, indicating that IG and BB could be beneficial for horses susceptible to obesity.

Conclusions

  • The findings of the research suggest that IG and BB could be viable alternatives to cool-season forages for horses susceptible to obesity as well as pasture-associated laminitis.
  • Despite lower consumption rates, these grasses displayed non-toxic characteristics and had low NSC levels safe for laminitis-prone horses.
  • However, it was noted that these horses can significantly reduce the grass cover during grazing, which may warrant further investigation in terms of sustainability for these types of grasses in the horse diets.

Cite This Article

APA
Ghajar SM, McKenzie H, Fike J, McIntosh B, Tracy BF. (2020). Evaluating digestibility and toxicity of native warm-season grasses for equines. Transl Anim Sci, 5(1), txaa224. https://doi.org/10.1093/tas/txaa224

Publication

Translational animal science
ISSN: 2573-2102
NlmUniqueID: 101738705
Country: England
Language: English
Volume: 5
Issue: 1
Pages: txaa224

Researcher Affiliations

Ghajar, S M
  • School of Plant and Environmental Sciences, Virginia Polytechnic Institute & State University, Blacksburg, VA.
McKenzie, H
  • Department of Large Animal Clinical Sciences, Virginia Polytechnic Institute & State University, Blacksburg, VA.
Fike, J
  • School of Plant and Environmental Sciences, Virginia Polytechnic Institute & State University, Blacksburg, VA.
McIntosh, B
  • Mars Equestrian™, McLean, VA.
Tracy, B F
  • School of Plant and Environmental Sciences, Virginia Polytechnic Institute & State University, Blacksburg, VA.

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Citations

This article has been cited 2 times.
  1. Weinert-Nelson JR, Meyer WA, Williams CA. Crabgrass as an equine pasture forage: impact of establishment method on yield, nutrient composition, and horse preference. Transl Anim Sci 2022 Apr;6(2):txac050.
    doi: 10.1093/tas/txac050pubmed: 35663614google scholar: lookup
  2. Weinert-Nelson JR, Meyer WA, Williams CA. Yield, nutrient composition, and horse condition in integrated crabgrass and cool-season grass rotational grazing pasture systems. Transl Anim Sci 2021 Oct;5(4):txab208.
    doi: 10.1093/tas/txab208pubmed: 34859200google scholar: lookup
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