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Scientific reports2026; 16(1); 3052; doi: 10.1038/s41598-026-35647-7

Feed intake, digestibility and passage kinetics in grazing horses.

Abstract: Feed intake and digestibility are important indicators for sufficient nutrient supply, but they can be assessed only to a limited extent in horses on pasture. In horses, feed intake is embedded in a complex behavioural pattern of searching, selecting, chewing and almost constant movement called foraging. The objectives of this study were to estimate organic matter intake (OMI) and organic matter digestibility (OMD) in six horses, 24 h/day on pasture, based on plant alkanes and synthetic n-hexatriacontane (C) excretion. A multi-compartmental model was fitted to the marker excretion and the C mean retention time (MRT) was estimated. The travelling activity influences the intestinal passage and digestion of the forage. For this reason, the travelled distances were tracked during the daylight hours (i.e., 13 h/day) by the global positioning system (GPS). The C MRT was 17.5 h based on an excretion curve, in which all horses were considered. Fitting individual excretion curves was less successful due to limited data points available for each horse. Depending on the plant marker, an OMI of 1.4 to 2.8% of body weight (BW)/day was estimated, which is analogous to a dry matter intake (DMI) of 1.5 to 3.1% of BW/day. The estimated OMD ranged from 0.45 to 0.68, dry matter digestibility (DMD) analogously from 0.39 to 0.65. The estimates obtained using n-nonacosane (C), followed by those obtained using n-hentriacontane (C), seemed to be the most plausible compared to the literature. Using C, a feed intake of 2.5% of BW/day (group) or 2.1% of BW/day (individuals) was estimated on organic matter basis, which was 2.7% of BW/day or 2.3% of BW/day on dry matter basis. An OMD of 0.64 and a DMD of 0.61 was estimated using C. Individually travelled distances ranged from 0.09 to 4.64 km in 1 h with differences detected among the days (p < 0.01), but not among the hours monitored within a day. Despite clear limitations, the methods seemed to be reliable to assess feed intake on pasture and to track movement activity. In modern husbandry systems, foraging should be as much unrestricted as possible to satisfy natural behavioural needs.
© 2026. The Author(s).
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Publication Date: 2026-01-22 PubMed ID: 41571885PubMed Central: PMC12830574DOI: 10.1038/s41598-026-35647-7Google 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.

Overview

  • This study aimed to estimate feed intake and digestibility of grazing horses using plant alkane markers and track their movement patterns with GPS.
  • Researchers used multi-compartmental modeling to understand how feed moves through the horse’s digestive system and related it to behavior and movement on pasture.

Introduction and Background

  • Feed intake and digestibility are key to ensuring horses receive adequate nutrients.
  • Measuring these parameters in grazing horses is challenging because intake happens continuously while they forage—searching, selecting plants, chewing, and moving almost constantly.
  • Foraging behavior affects digestion and nutrient absorption, making it important to study under natural pasture conditions.

Objectives

  • Estimate the amount of organic matter intake (OMI) and organic matter digestibility (OMD) for horses grazing 24 hours a day on pasture.
  • Use plant alkanes (natural chemical markers in plants) along with a synthetic marker called n-hexatriacontane (C) to track feed intake and digestion.
  • Model the passage kinetics (how long feed stays in the digestive tract) using a multi-compartmental model fitted to marker excretion data.
  • Assess the influence of horses’ movement activity on digestion by tracking distances traveled during daytime using GPS.

Methods

  • Six horses were continuously grazed on pasture for 24 hours/day.
  • Feed intake was estimated by analyzing the excretion of natural plant alkanes and the synthetic alkane marker n-hexatriacontane in feces.
  • A multi-compartmental model was used to fit alkane excretion data and determine mean retention time (MRT) of feed in the digestive system.
  • GPS tracking devices recorded the horses’ traveled distances during daylight (13 hours/day) to study movement patterns.

Key Findings

  • The mean retention time of the synthetic marker (C) in the digestive tract was about 17.5 hours.
  • Feed intake estimates varied depending on the marker used:
    • Organic matter intake (OMI) ranged between 1.4% and 2.8% of body weight (BW) per day, translating to dry matter intake (DMI) of 1.5% to 3.1% BW/day.
    • Digestibility estimates varied from 0.45 to 0.68 for organic matter digestibility (OMD), and 0.39 to 0.65 for dry matter digestibility (DMD).
  • The markers n-nonacosane and n-hentriacontane gave the most plausible intake and digestibility estimates compared to published data.
  • Using the synthetic marker C, group feed intake was estimated at 2.5% BW/day organic matter (2.7% dry matter), with OMD = 0.64 and DMD = 0.61.
  • GPS data showed significant day-to-day differences in hourly distances traveled (range 0.09 to 4.64 km/hr), though no significant difference among hours within the same day.

Discussion and Implications

  • The study demonstrates that plant alkanes and synthetic alkane markers can reliably estimate feed intake and digestibility in grazing horses despite practical challenges.
  • The multi-compartmental modeling approach effectively characterized passage kinetics, critical to understanding digestion in free-ranging animals.
  • Tracking movement via GPS provided insight into how travel activity influences digestion and feed passage through the gut.
  • Findings emphasize the importance of allowing horses extensive opportunity to forage naturally in modern management systems to fulfill behavioral needs and ensure proper nutrition.
  • This combined methodological approach can improve feeding management and welfare of horses by providing quantitative data on intake and digestive efficiency in pasture-based systems.

Limitations

  • Individual excretion curves were less precise due to limited fecal sample data points per horse.
  • Some variability in intake and digestibility estimates depending on the marker used.
  • GPS tracking limited to daylight hours only, potentially missing night-time movement behavior.

Cite This Article

APA
Bachmann M, Bochnia M, Wensch-Dorendorf M, Glatter M, Schäfer S, Simroth K, Greef JM, Zeyner A. (2026). Feed intake, digestibility and passage kinetics in grazing horses. Sci Rep, 16(1), 3052. https://doi.org/10.1038/s41598-026-35647-7

Publication

Scientific reports
ISSN: 2045-2322
NlmUniqueID: 101563288
Country: England
Language: English
Volume: 16
Issue: 1
Pages: 3052
PII: 3052

Researcher Affiliations

Bachmann, Martin
  • Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany. martin.bachmann@landw.uni-halle.de.
Bochnia, Mandy
  • Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
Wensch-Dorendorf, Monika
  • Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
Glatter, Maren
  • Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
Schäfer, Stephan
  • Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
Simroth, Katrin
  • Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
Greef, Jörg M
  • Institute for Crop and Soil Science, Julius Kühn Institute, Federal Research Centre for Cultivated Plants, Braunschweig, Germany.
Zeyner, Annette
  • Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany. annette.zeyner@landw.uni-halle.de.

MeSH Terms

  • Animals
  • Horses / physiology
  • Digestion / physiology
  • Eating / physiology
  • Animal Feed
  • Male
  • Feeding Behavior / physiology
  • Kinetics
  • Female

Conflict of Interest Statement

Declarations. Competing interests: The authors declare no competing interests.

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