Grass awns are small, sharp, seed-bearing structures found on the seed heads of several common grasses. Once dried, they become rigid, barbed projectiles that easily attach to fur and penetrate skin, posing a significant threat to domestic animals. The danger lies in their physical design, which allows them to migrate relentlessly through tissue, causing pain, infection, and potential organ damage if not addressed promptly.
Botanical Definition and Function
An awn is botanically defined as a slender, bristle-like appendage that extends from the floral bracts of a grass spikelet. This outgrowth is a specialized structure designed to assist in the plant’s reproductive strategy of seed dispersal and burial. The physical appearance is typically a stiff, elongated projection that varies in length depending on the grass species. Grasses such as foxtail, cheatgrass, wild barley, and spear grass are well-known for producing these problematic awns.
The natural function of the awn is twofold: aiding in seed dispersal by catching the wind or hitching onto the fur of passing animals (epizoochory), and helping the seed bury itself into the soil for germination. This self-burial mechanism is closely linked to the awn’s dangerous physical properties.
The Physical Mechanism of Penetration
The danger of grass awns stems from their unique design for unidirectional movement. The surface of the awn is covered in microscopic, backward-facing scales or barbs, giving it an arrow-like or ratchet structure. This design means the awn can easily push forward into soft material, such as skin or tissue, but is physically resisted from moving backward.
Once the awn has pierced a barrier, any subsequent movement of the surrounding tissue, such as walking or muscle contraction, acts to propel the awn deeper. Furthermore, many awns are hygroscopic, meaning they respond to changes in moisture. As the awn absorbs and releases moisture, it expands and contracts, causing a twisting motion that effectively “walks” the seed deeper into the host animal’s body.
Common Health Risks in Pets
The migration of grass awns into a pet’s body can cause a range of severe health issues, dependent on the point of entry. Paws are a frequent target, where awns lodge between the toes or paw pads, leading to painful swelling, abscess formation, and lameness. A draining tract may appear as the body attempts to expel the foreign object, and the pet will often lick the area incessantly.
The ears are another common entry site, particularly for active dogs running through tall grass. An awn entering the ear canal can cause intense irritation, leading to excessive head shaking, pawing at the ear, and secondary ear infections, with a potential for eardrum rupture. If inhaled through the nose, the awn triggers violent, persistent sneezing fits and nasal discharge, sometimes bloody, as it attempts to burrow deeper into the nasal passages.
In more serious cases, an inhaled awn can travel down the respiratory tract into the lungs, potentially causing severe pneumonia or pyothorax (an accumulation of pus in the chest cavity). Awns may also target the eyes, causing irritation, redness, excessive tearing, and corneal ulcers. From any entry point, the awn can continue to migrate internally, leading to deep-seated abscesses and, rarely, reaching vital organs where it can cause peritonitis or other systemic infections.
Prevention and Safe Removal
Pet owners can significantly reduce the risk of awn-related injury by taking proactive preventative measures, especially during the late spring and summer when grasses dry out and seeds are prevalent. Avoiding walks in tall, overgrown grassy fields is the most direct way to prevent exposure. For dogs that frequently explore such areas, protective gear like dog boots may help shield the paws.
Routine grooming is an important defensive action, particularly trimming the fur between the toes and around the ears to minimize surface area for attachment. After any outdoor activity in grassy environments, a thorough inspection of the pet should be performed. Owners should pay close attention to the common entry points:
- Ears
- Eyes
- Nose
- Spaces between the paw pads
If a grass awn is found loosely snagged in the fur, it can be carefully removed with tweezers or a brush. However, if the awn has already punctured the skin, entered an orifice, or disappeared beneath the surface, immediate veterinary attention is necessary. Attempting to pull out an embedded awn can cause it to break apart, leaving fragments behind to continue migrating and increasing the risk of severe infection, necessitating surgical removal.