Role of Tannins in Defending Plants Against Ruminants: Reduction in Dry Matter Digestion?

Area of Science:

• Animal Nutrition
• Plant-Herbivore Interactions
• Biochemistry

Background:

• Polyphenolic allelochemicals like tannins are believed to decrease plant digestibility in herbivores by inhibiting digestive enzymes and proteins.
• While tannins reduce protein and cell soluble digestibility in deer, they do not affect plant cell wall digestion as predicted by lignin, cutin, and silica content.

Purpose of the Study:

• To investigate the unique mechanisms by which deer (Odocoileus hemionus and O. virginianus) digest tanniferous forages.
• To identify and compare salivary proteins in mule deer, cattle, and sheep and their role in mitigating tannin effects.

Main Methods:

• Comparative analysis of saliva composition in mule deer, domestic cattle, and sheep.
• Evaluation of the in vitro and in vivo effects of tannins on digestive processes in ruminants.

Main Results:

• Deer saliva exhibits a higher potential to neutralize tannins compared to cattle and sheep saliva.
• The study identified specific salivary proteins in ruminants that bind tannins, a finding reported for the first time.
• Tannin-binding salivary proteins in deer are linked to their mixed-feeding habits, enabling efficient consumption of browse.

Conclusions:

• Deer possess specialized salivary proteins that bind tannins, protecting cell wall digestion and allowing for effective forage utilization.
• These salivary adaptations in deer minimize nitrogen loss and reduce the absorption of potentially toxic hydrolyzable tannins.
• The findings highlight a novel defense mechanism in herbivores against plant allelochemicals, with implications for animal nutrition and ecology.