Not all lame livestock are created equally.
By: Russ Daly, SDSU Extension Veterinarian and Associate Professor
Our last column, Limping Livestock: Two Perspectives, examined limping livestock from two different viewpoints: that of the stockman and that of the general public. With this entry, we begin to look more closely at the root causes of the lameness experienced by that animal.
To anyone who has raised animals, it’s apparent that not every lame animal is created equal. There is a wide gradation of clinical signs, with some animals exhibiting obvious "dead" lameness, while other cases of lameness almost escape detection.
Let’s start with the trickiest scenario first: subtle cases of lameness. Large animals, especially cattle and sheep, are prey animals by nature. It is not in their programming to easily reveal any weakness, illness, or injury to a predator (people can be viewed as predators), and lameness certainly qualifies in this regard. Therefore, animals with even relatively severe musculoskeletal conditions may mask lameness rather well until the condition deteriorates. This poses challenges for livestock caretakers who wish to detect and treat cases of lameness in their early stages. Additionally, certain conditions that affect the feet and limbs may be rather subtle at first. In fact, researchers -- partly in order to quantify lameness and partly because lameness conditions they study may be quite subtle – sometimes resort to technology such as pressure-sensitive pads that detect minor changes in gait or weight-bearing when the animals walk across them.
Of course, these high tech instruments are not readily found in cattle operations today, so experienced and careful observation becomes important. One of the first observable clinical changes in a lame animal occurs when the animal’s stride is shortened. For example, the normal gait of a calf is that of long strides, with the frontward motion of the rear leg and foot being placed very close to where the same-side front hoof was planted. When an animal is lame in one limb, that limb tends to have a shorter stride than normal. Zinpro Corporation has produced a Locomotion Scoring System website that illustrates this well.
Another subtle indication of lameness is observed not in the limbs, but rather the head of the animal. When the animal plants a painful foot (especially a painful front foot), the animal’s head is often observed to "bob" upward – a distinct difference from a normal gait in which the head stays more or less level to the ground during walking.
As animals become more severely affected and more painful, these signs of shortened stride, head bobbing, and arching of the back become more pronounced, to the point where an animal will avoid bearing weight on the affected limb.
In the worst cases, the animal will refuse to touch the limb to the ground and will prefer to walk three-legged. This typically means there is a severe problem – an extremely painful situation, a fracture, or a dislocation.
A future article in this series will examine different causes of lameness in livestock, but we can assume that animals who exhibit any of the clinical signs described above have one root cause in common – pain. In essentially all causes of lameness, the animal’s gaits are affected because it is too painful to move in a normal fashion. This pain can arise from anywhere in the affected limb, and the causes are numerous. Pain may arise from an injury to the hoof (a crack or a nail extending into the sensitive part of the hoof wall), a sprain or strain of ligaments, tendons, or joint structures, a soft tissue injury or infection (such as hoof rot), or a fracture or dislocation of a bone or joint.
Another future article will look at diagnosis of lameness, but one should consider for all practical purposes that a lame animal is an animal that is experiencing pain. One should understand that, as injuries or infections progress from acute to chronic, it is possible that the pain experienced by an animal may dull somewhat due to increased scarring and healing, or potentially due to adaptation by the animal. And it is very common for an animal to "forget" about a painful condition when a stressful situation arises and adrenaline kicks in, for example when an animal flees from a perceived threat. Such animals are in danger of inflicting more damage upon themselves and the handler in such cases.