Feed intake, digestibility and passage kinetics in grazing horses

Area of Science:

• Equine Nutrition
• Animal Science
• Digestibility Studies

Background:

• Assessing feed intake and digestibility in horses on pasture is challenging due to complex foraging behaviors.
• Nutrient supply is crucial for horse health, and accurate intake/digestibility measures are vital.
• Foraging behavior in horses involves intricate patterns of searching, selecting, chewing, and constant movement.

Purpose of the Study:

• To estimate organic matter intake (OMI) and organic matter digestibility (OMD) in horses grazing pasture 24 hours daily.
• To utilize plant alkane excretion and synthetic n-hexatriacontane (C36) as markers for intake and digestibility estimation.
• To investigate the influence of traveling activity on intestinal passage and forage digestion in grazing horses.

Main Methods:

• Employed plant alkanes and synthetic n-hexatriacontane (C36) to assess marker excretion.
• Utilized a multi-compartmental model to estimate C36 mean retention time (MRT).
• Tracked horse traveling distances using GPS during daylight hours (13 h/day) to correlate with digestive processes.

Main Results:

• Estimated OMI ranged from 1.4 to 2.8% of body weight (BW)/day, analogous to dry matter intake (DMI) of 1.5 to 3.1% BW/day.
• Estimated OMD ranged from 0.45 to 0.68, with dry matter digestibility (DMD) ranging from 0.39 to 0.65.
• n-Nonacosane (C29) and n-hentriacontane (C31) provided the most plausible digestibility estimates compared to literature values.

Conclusions:

• The alkane-based method, particularly using C29, appears reliable for assessing equine feed intake and digestibility on pasture.
• Horse movement, tracked via GPS, influences digestive passage, highlighting the importance of considering activity in nutritional studies.
• Allowing unrestricted foraging behavior in modern husbandry systems is essential for meeting horses' natural behavioral needs.