Graminivores

Graminivores, or graminivorous animals, are those that primarily feed on grass, particularly ‘true grasses’ of the family Poaceae. This grass-heavy feeding strategy is referred to as graminivory, and graminivores are structurally and behaviorally adapted to make grass a major part of their diet.

Although graminivory is a type of herbivory, it is more specific. While a herbivore eats plants in general, a graminivore depends mainly on grass rather than a broad mix of plant parts.

This distinction is also important when comparing graminivores with other plant-feeding animals, especially grazers and browsers. A grazer feeds on low-growing vegetation and is often grass-eating, but grazing describes the feeding behavior, while graminivory describes a dietary type. Similarly, a browser feeds mainly on leaves, shoots, shrubs, or woody plants, even though they may sometimes eat grass.

Feeding Adaptations

Although grass may seem to be a simple and abundant food source, it is rich in fibrous cellulose, which is extremely hard to digest. Moreover, grass can also be abrasive, so animals that eat it regularly need ways to grind it, process it, and then extract nutrients from it.

Thus, graminivores have adapted to different adaptations for digesting grass.

Foregut fermentation: Some graminivores have a specialized foregut where microbes break down or ferment grass before it reaches the main stomach or intestine. Because fermentation happens early, the animal can absorb more nutrients from the microbial breakdown of cellulose.¹

Hindgut fermentation: Some graminivores ferment grass after it passes through the stomach and small intestine, usually in enlarged hindgut chambers such as the cecum or colon.²

Mechanical grinding: Some graminivores rely heavily on physical grinding to break down grass. They may achieve this through broad grinding teeth, specialized serrated bills³, a muscular grinding organ (crop), or other structures that crush plant material before or during digestion.

Cutting and Chewing: Smaller graminivores typically use mouthparts that are adapted to cut, scrape, or shred grass before it enters the gut for digestion.

Common Examples

The following table lists the common examples of graminivores, based on their feeding adaptations.

Animal Group	Feeding Adaptation	Examples
Mammals	Foregut Fermentation	Cows, buffaloes, sheep*, goats, antelopes*, bison
	Hindgut Fermentation	Horses, zebras, rhinoceroses*, capybaras*, guinea pigs*
Birds	Mechanical Grinding	Geese and some ducks
Insects	Cutting and Chewing	Grasshoppers, crickets*, and some caterpillars*

*These animals are not always strict graminivores. They may eat grass as a major part of the diet in some conditions, while also feeding on other plants or plant parts. 

As herbivores, these animals shape the ecosystems they live in. By feeding on grass, they can influence which plants grow and how tall the vegetation of a particular region becomes.⁴ Also, graminivores are prey for several carnivorous animals, and thereby form an indispensable part of the food web.