Pasture Violence: Not to be Ignored

By Gabriel Denison

It was exactly forty-eight hours after I'd dropped the two horses off in the shared pasture. I was not prepared for what I found. Oklahoma Girl, a senior roan mare, had lost about 100 pounds. The skin on her chest hung in deep folds, and her eyes were sunken: both signs of serious dehydration. Her slender neck was swollen and covered with bites.

I walked her to the safety of a friend's house, and tried to make her comfortable, but the next morning, abscesses had started. Broken Top vet, Little Leiblad warned me how cellulitus (an infection of the soft tissue from bruising) can be fatal. We tried to save her, but when I drove up the following morning, I saw her fall in the summer grass. On the forth morning since I put her on pasture, my mare was dead, a victim of pasture violence, or herd aggression.

Aggression within the herd structure is not an uncommon problem, but one that can have serious results. Equine aggression can take several forms, according to research done at the Equine Behavior Program at University of Pennsylvania:

•  Group Aggression, to establish territory and place value –also known as pecking order – which includes threatening behaviors. These can be biting, kicking and lunging at herd mates, or running the new horses. Horses have been known to aggressively pursue victims to exhaustion, and through fences.

•  Dominant behavior by a mare or gelding towards a single horse. This may include cutting the victim out of the group, and is dangerous if the isolated horse is kept from food and water.

•  Gelding Aggression, in which a gelding will display residual stallion-like behaviors. These include grasping, shaking and holding the neck at the throat or jugular area, causing severe swelling and related complications.

Leslie Gill, DVM, an exclusive equine specialist in Tumalo, reports that overt aggression in mares or geldings can be of a hormonal nature.

“Gelding aggression can result from retained testicular tissue, a condition known as cryptorchid. Mare aggression can result from a granulosa cell tumor. This is a tumor in the ovaries that causes an overactive testosterone secretion, and both conditions can be easily identified through a blood workup on the horse.”

But there are other considerations. “There is evidence of a genetic link within the hierarchy of herd structure,” she says, “ and some horses are naturally timid. If paired with an aggressive horse, these horses are targets.”

According to Dr. Gill, gray horses are the recipients of more herd aggression than dark horses, and seem to be consistently at the bottom of herd structures.

Dr. Gill's advice on preventing grievous pasture aggression incidents is thorough. Firstly, she advises that the aggressive horse be kept separate, and not placed in situations where other animals are at risk. Secondly, owners should be aware of tight corners or sheds where aggressive horses can corner more timid animals and subject them to repeated kicking with no escape. Thirdly, empower your horse by walking him around the fenceline before releasing him, so he is aware of the boundaries.

Other suggestions are to keep mares and geldings in separate groups, or allow your horse to bond with another animal from within the herd, and release them together. She does not, however, recommend introductions through fences. Owners should stay and observe the herd interaction before leaving their horse in a strange group, and never drop your horse in his new pasture around feeding time.

“Remember,” Dr.Gill continued, “Changing the structure of the herd is stressful in the best of conditions. When you introduce new horses to a herd, you are changing the existing herd structure, and there is a potential risk for injury.”

All horse lovers can follow the three R's of pasture violence: Resist, by responsibility in managing your horse. Report, if you see any aggressive or unusual behavior between pasture mates, or signs of violence on a herd animal. Reimburse, if your horse contributes to the injury or death of another, offer to financial assistance to the injured. With our help, our horses can live safer lives, and still frolic in the green fields of Central Oregon.