How do animals spread weed seeds after eating grasses?

Animals spread weed seeds after consuming grasses primarily through a process known as endozoochory. When grazing animals—such as birds, small mammals, and large herbivores—eat grasses, they ingest the seeds along with the plant material.123

For this dispersal method to be successful, the seeds must remain intact and viable as they pass through the animal's digestive tract. Once the animal defecates, the seeds are deposited in a new location, often accompanied by nutrients from the feces that can aid in their germination and establishment. This process is distinct from seed predation (granivory), where seeds are digested and destroyed; instead, endozoochory functions as a mutualistic relationship that facilitates the spread of various plant species, including weeds.1

Additionally, some grasses have evolved physical adaptations, such as barbs, spines, or hairs on their spikelets, that allow them to attach to the exterior of animals (epizoochory), further assisting in their dispersal as animals move through the environment.32