A comparison of fecal output determined by total fecal collection or titanium dioxide in horses.

Overview

• This research studied whether titanium dioxide (TiO2) can reliably estimate fecal output in horses using spot samples instead of the more labor-intensive total fecal collection method.
• The study conducted two experiments comparing fecal output measured by total collection (actual fecal output, aFO) and by TiO2 concentration in fecal spot samples (calculated fecal output, cFO) under different feeding strategies and diets.

Background and Objective

• Total fecal collection methods for measuring digestibility in horses are accurate but costly and labor-intensive.
• Using externally dosed indigestible markers such as TiO2, measured in fecal spot samples, could simplify estimating fecal output.
• Before this method can be widely used in horses, its accuracy and reliability must be validated due to limited existing research.
• The objective was to compare fecal output calculated from TiO2 in fecal spot samples to actual total fecal output in horses under different feeding conditions.

Experimental Design

• Experiment 1:
  • Subjects: Four mature horses.
  • Diet: Forage-based diet (85% forage, 15% concentrate).
  • Feeding: Twice daily meals, each top-dressed with TiO2 (1.75 g TiO2 per kg dry matter, about 10 g total per day).
  • Procedure: TiO2 fed for 10 days, followed by 4 days of total fecal collection.
  • Data collection: Fecal samples every 4 hours to measure TiO2 excretion and calculate fecal output (cFO), compared to total fecal output (aFO).
• Experiment 2:
  • Subjects: Fifteen horses divided into three diet groups differing in forage content: Low forage (LO, 45%), Medium forage (MED, 73%), High forage (HI, 95%).
  • Diet Delivery: Daily ration divided into three equal meals with TiO2 thoroughly mixed at 2 g/kg dry matter per day.
  • Procedure: TiO2 fed for at least 12 days before 5 days of total fecal collection.
  • Fecal samples collected every 4 hours as in Exp 1 to calculate cFO and compare to aFO.

Results

• Experiment 1:
  • Calculated fecal output (cFO) overestimated actual fecal output (aFO) by 10% across all horses and days.
  • Correlation between cFO and aFO was weak and statistically nonsignificant (R² = 0.148, P > 0.10), indicating poor predictive accuracy from spot samples.
• Experiment 2:
  • When averaged across all horses and days, cFO was not significantly different from aFO, showing better agreement at the group level.
  • However, cFO was significantly different from aFO for 10 out of 15 individual horses, indicating variability between animals.
  • Fecal output estimated by TiO2 underestimated actual fecal output in horses fed the high-forage (HI) diet compared to the medium and low forage diets.
  • The variability and discrepancies were affected by diet composition and individual differences.

Interpretation and Implications

• TiO2 as an indigestible marker in fecal spot samples showed potential for estimating fecal output but with considerable variability and inaccuracies on an individual horse basis.
• Top-dressing TiO2 on meals and feeding twice daily (Exp 1) led to consistent overestimation and poor correlation.
• Mixing TiO2 thoroughly in feed and feeding three times daily (Exp 2) improved accuracy at the group level but still showed poor accuracy for many individual horses.
• High-forage diets may reduce the accuracy of TiO2-based fecal output estimates, possibly due to differences in digestion or marker passage.
• Large within-horse variability in fecal TiO2 concentration complicates reliable fecal output calculation from spot samples.
• Overall, the TiO2 method needs optimization (e.g., dosing, sampling frequency, diet adjustments) before replacing total fecal collection as a standard method in horses.

Conclusion

• The use of TiO2 in fecal spot samples does not yet provide a consistently accurate substitute for total fecal collection in estimating horse fecal output.
• Further research is required to refine the methodology to reduce variability and improve individual animal accuracy, especially under different dietary regimes.