Faecal particle size: digestive physiology meets herbivore diversity

Area of Science:

• Ecophysiology
• Comparative physiology
• Animal science

Background:

• Comparative chewing efficiency in large herbivores is a recent research focus.
• Existing datasets for unprocessed forage diets are limited.
• Chewing efficiency is crucial for understanding herbivore digestive strategies.

Purpose of the Study:

• To assess faecal mean particle size (MPS) as a measure of chewing efficiency in 14 large herbivore species.
• To investigate the relationships between MPS, digesta mean retention times (MRT), and digestive efficiency.
• To explore how these factors relate to body mass and phylogenetic relatedness.

Main Methods:

• Measured faecal mean particle size (MPS) in 14 large herbivore species on a consistent grass hay diet.
• Quantified intake, digesta mean retention times (MRT), and digestive efficiency (GP96h, MFN) simultaneously.
• Analyzed correlations between MPS, MRT, body mass, and digestibility metrics.

Main Results:

• Faecal mean particle size (MPS) was lower in ruminants than hindgut fermenters and increased with body mass.
• MPS correlated with in vitro gas production (GP96h), while MRT correlated with metabolic faecal nitrogen (MFN).
• Combinations of measures including MPS explained digestibility better than single measures, reducing phylogenetic signal.

Conclusions:

• Chewing efficiency, measured by faecal particle size, is a key factor in large herbivore digestive physiology and species diversification.
• Digestive strategies are influenced by a combination of factors including chewing efficiency and digesta retention time.
• Phylogenetic relatedness plays a role, but functional traits like chewing efficiency are critical for explaining digestive adaptations.