Stringhalt in cattle
The stifle in cattle is the joint in the flank and is equivalent in structure and function to the human knee. The kneecap in cattle (the pointy end of the round) has three ligaments (humans have only one) extending from it down to join onto the tibia, which is the main bone between the stifle and the hock. Stringhalt in cattle is due to the inside ligament becoming hooked over the top of the knee, i.e. a virtual dislocation, and is technically called a ‘dorsal luxation’ or ‘upward fixation’. (Horses purposely lock their kneecap in this way when standing at rest).
In cows, upward fixation locks the hind leg into extension until the animal can disengage it. The leg is seen to be straight and back with the hoof being dragged along the ground. When the ligament disengages, the leg jerks forward and animals move reasonably freely until the ligament hooks up again. The condition can be treated surgically, but as it is more likely of genetic origin, disposal of affected animals is almost universally recommended.
This condition is very different to stringhalt in horses, which is related to problems with a muscle and tendon that passes over the outside of the hock.
- Defective knee structure and function. This could be poorly-arranged skeletal, muscle or tendon structures combined with general poor muscle tone and bulk with loss of body condition.Reasons why this is likely are:
- Stringhalt is usually restricted to particular lines of cattle in a number of breeds and appears most common in Bos indicus breeds.
- In herds that have stringhalt, cattle as young as suckling calves have demonstrated the symptoms when closely observed.
- Cattle in good condition often do not show the typical locked-leg symptoms. When the same cattle lose condition, due to poor seasonal conditions, lactation, etc, stringhalt becomes evident. It is believed that cattle with plenty of muscle bulk and good muscle tone (in good condition) have the ability to prevent the ligament hooking up and upward fixation occurring. As they lose condition, their ability to prevent the ligament hooking up declines. As the same cattle improve in body condition there is less evidence of stringhalt. Cattle identified with stringhalt should be segregated for preferential nutritional management (better feed, prevention of pregnancy, etc) before disposal.
- Stringhalt is more common where nutrition is poorest, despite normal bone composition. But the same poor nutrition does not result in stringhalt expression in most herds.
Anatomical defect is probably the most likely cause of stringhalt.
- Injury to knee structures. This may be the cause when the condition appears suddenly. This may occur when cattle slip, for example, when riding other cows in oestrus, while their hind legs are in extension.
- Physiological disorders. Examples include specific mineral deficiencies such as calcium and phosphorus. This is more likely during late pregnancy and lactation when severe deficiencies can also cause other temporary abnormal skeletal changes e.g. ‘peg leg’. It is most likely that such disorders also require some degree of the above-mentioned anatomical defect to achieve expression of stringhalt.
The elimination of stringhalt is likely to be long term and focus around culling animals exhibiting symptoms. In potential breeding animals, particularly bulls, the stifle should be carefully examined during walking. As the condition is much less evident in cattle in good condition it is often a relatively slow process to breed out of a herd. For this reason careful selection of bulls is important.
Geoffry Fordyce, Queensland Alliance for Agriculture and Food Innovation.