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Journal of animal science2019; 97(6); 2541-2554; doi: 10.1093/jas/skz103

Effects of grazing system, season, and forage carbohydrates on glucose and insulin dynamics of the grazing horse.

Abstract: Rotational grazing is a recommended practice for grazing livestock, but little is known about its benefits with respect to grazing horses. The objective of this study was to investigate the effects of continuous (CON) and rotational (ROT) grazing on forage nutrient composition and whether those concentrations influenced circulating glucose and insulin concentrations in the grazing horse. Twelve mature Standardbred mares were paired by age and weight and randomly assigned to 1 replicate of either a 1.5 ha cool-season grass CON or ROT system for a total of 3 mares in each system. Mares on CON were allowed to graze the entire system at all times, whereas mares on ROT were given access to a 0.4 ha pasture section and stress lot where they were confined during inclement weather and slow forage growth. Blood and feces from horses and forage from each system were sampled over one 24-h period in June, August, and October. Blood was assessed for plasma glucose (GLU) and serum insulin (INS), feces for pH, and forage for nutritional composition. Data were analyzed by ANOVA with repeated measures with significance set at P < 0.05. There were no treatment differences for water and ethanol soluble carbohydrates (WSC and ESC, respectively), starch, ADF, and NDF, but CP was lower in ROT compared to CON (P = 0.04). With respect to month, WSC were highest in June compared to August and October, whereas ESC were highest in June compared to only August. Starch was lower in October than in June and August. Concentrations of ADF and NDF were lowest in October compared to June and August. Crude protein was higher in October than June and August. Plasma GLU and serum INS were affected by season and time of day but not grazing system. For all horses, GLU was highest in August (105.6 ± 1.3 mg/dL), whereas INS was highest in October (0.21 ± 0.02 μg/L; P < 0.0001). Fecal pH only varied by season and was highest in August (7.06; P < 0.0001). Few consistent correlations between grazing systems were found with the exception of INS with ESC (R = 0.32 to 0.39; P < 0.04) and INS and GLU with ADF and NDF in August and October (R = -0.31 to -0.48; P < 0.04). In conclusion, grazing system did not affect the forage carbohydrate concentrations or GLU or INS in horses; however, season did have an effect on both forage nutrient content and glucose metabolism in horses.
© The Author(s) 2019. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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Publication Date: 2019-03-27 PubMed ID: 30911753PubMed Central: PMC6541809DOI: 10.1093/jas/skz103Google Scholar: Lookup
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Summary

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This study investigated the impacts of different grazing systems—continuous and rotational—on the nutrient composition of forage and whether those concentrations influenced glucose and insulin levels in horses. The results revealed no significant differences related to the grazing system used but confirmed seasonal variations in both forage nutrient content and glucose metabolism in horses.

Research Design and Methodology

  • The study involved twelve mature Standardbred mares, which were paired by age and weight. These mares were allocated either to a 1.5 ha cool-season grass continuous grazing system or a rotational grazing system, with three mares in each system.
  • The mares in the continuous system were allowed to graze freely at all time in the entire system. However, those under the rotational system were given access to a 0.4 ha pasture section. They were confined during inclement weather and periods of slow forage growth.
  • Over the course of a year – in June, August, and October – the researchers collected samples of blood and feces from the horses and forage from each system. These samples were then assessed for specific nutritional components and chemical substances.

Key Findings

  • No significant differences were observed in water and ethanol soluble carbohydrates, starch, ADF (Acid Detergent Fiber), and NDF (Neutral Detergent Fiber) between the two grazing systems. However, crude protein was lower in rotationally grazed horses compared to continuously grazed horses.
  • When examining seasonal differences, water soluble carbohydrates were most abundant in June, while ethanol soluble carbohydrates were highest in June compared to August. Starch was lowest in October as compared to June and August. The lowest concentrations of ADF and NDF were recorded in October. The crude protein levels were higher in October than in June and August.
  • Plasma glucose and serum insulin were affected by the season and time of day but not by the grazing system. The concentration of glucose was highest in August, whereas insulin was highest in October. Fecal pH only varied by season and was highest in August.

Conclusions

Based on the results, the study concluded that the type of grazing system did not significantly influence the forage carbohydrate concentrations or glucose or insulin levels in horses. However, seasonal changes did affect both the nutrient content of the forage and the glucose metabolism in horses.

Cite This Article

APA
Williams CA, Kenny LB, Burk AO. (2019). Effects of grazing system, season, and forage carbohydrates on glucose and insulin dynamics of the grazing horse. J Anim Sci, 97(6), 2541-2554. https://doi.org/10.1093/jas/skz103

Publication

Journal of animal science
ISSN: 1525-3163
NlmUniqueID: 8003002
Country: United States
Language: English
Volume: 97
Issue: 6
Pages: 2541-2554

Researcher Affiliations

Williams, Carey A
  • Department of Animal Science, Rutgers, The State University of New Jersey, New Brunswick, NJ.
Kenny, Laura B
  • Department of Animal Science, Rutgers, The State University of New Jersey, New Brunswick, NJ.
Burk, Amy O
  • Department of Animal and Avian Sciences, University of Maryland, College Park, MD.

MeSH Terms

  • Animal Feed / analysis
  • Animals
  • Blood Glucose / analysis
  • Body Weight
  • Carbohydrates / analysis
  • Feces / chemistry
  • Female
  • Horses / physiology
  • Hydrogen-Ion Concentration
  • Insulin / blood
  • Poaceae
  • Random Allocation
  • Seasons
  • Weather

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Citations

This article has been cited 7 times.
  1. Lopes A, Huber L, Durham AE. The Seasonality of Serum Insulin Concentrations in Equids and the Association With Breed, Age, and Sex. J Vet Intern Med 2025 May-Jun;39(3):e70089.
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  2. Thane K, Sonntag J, Warnken T, Reiche D, Uricchio C, Frank N. Comparison of a customized glycemic pellets challenge with the oral sugar test to measure glycemic and insulinemic responses in horses. J Vet Intern Med 2024 Nov-Dec;38(6):3281-3287.
    doi: 10.1111/jvim.17191pubmed: 39463160google scholar: lookup
  3. Viviani P, Lavado RA, Chavarria NH, Ragno VM, Montgomery JB. Spring and fall blood concentrations of adrenocorticotropic hormone, insulin, and thyroxine in healthy horses in Saskatchewan. Can Vet J 2024 Apr;65(4):335-342.
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  4. Weinert-Nelson JR, Biddle AS, Sampath H, Williams CA. Fecal Microbiota, Forage Nutrients, and Metabolic Responses of Horses Grazing Warm- and Cool-Season Grass Pastures. Animals (Basel) 2023 Feb 22;13(5).
    doi: 10.3390/ani13050790pubmed: 36899650google scholar: lookup
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  7. Williams CA, Kenny LB, Weinert JR, Sullivan K, Meyer W, Robson MG. Effects of 27 mo of rotational vs. continuous grazing on horse and pasture condition. Transl Anim Sci 2020 Jul;4(3):txaa084.
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