Curly toe paralysis presents as inward curling of the toes on the chicken's feet, which impairs their ability to walk. Affected birds may be seen walking or resting on their hocks. The condition occurs when the sciatic nerves are damaged. The two most common causes of this condition in chicks are Marek's disease and riboflavin (Vitamin B2) deficiency.
Riboflavin is one of the vitamins most likely to be deficient in commercial chicken feeds. Only a few feedstuffs fed to chickens contain enough riboflavin to meet the requirements of young growing chicks or breeding hens producing eggs to be hatched. Feeds which utilize corn or soybean meal as the primary ingredient are more likely to be deficient in riboflavin. Riboflavin is easily destroyed upon exposure to ultraviolet (UV) rays or sunlight. Therefore if chickens are fed outside the portion of the feed exposed to light won't contain much riboflavin.
Chicks with curly toe paralysis will slowly develop progressive symmetrical paresis and weakness. Affected chicks soon become reluctant to move, followed by intermittent flexing and inward curling of toes. Without use of the legs, the muscles in the legs will start to atrophy and may eventually extend outward out from underneath the body of the chick. During advanced stages of this condition, chicks are seen more frequently resting on their hocks, trying to walk as little as possible. It is at this later stage that chicks are at high risk of death from starvation, due to inability to reach food or water sources, or from getting trampled on by other chicks.
Nutritional Riboflavin Requirements
Nutritional riboflavin requirements for chickens fluctuate depending on genetics, stage of growth, environmental conditions, level of activity, health status, and other dietary components and synthesis. Riboflavin requirements are highest for newly hatched chicks and for chickens used for breeding. The NRC (1994) recommends that poultry species require between riboflavin at 1.8 - 4 mg/kg (0.45 - 1.8 mg/lb) of diet. However, more recently conducted research studies have found that NRC's recommendation is not sufficient for modern breeds of chickens, breeders, or growing chicks. All chickens should receive a diet with a minimum riboflavin content of 4.4 mg/kg (2.0 mg/lb). Recommended riboflavin levels from DSM Nutrition are as follows:
|Newly Hatched Chicks (0 - 10 wks)||6 to 7|
|Young & Growing (10 - 20 wks)||5 to 6|
|Laying hens (Actively laying eggs)||5 to 7|
|Breeders (20 wks & older)*||10 to 12|
|Broiler/'Meat' Breed Chicks (0-18 wks)||6 to 8|
|Broiler/'Meat' Breeds* (19 wks & older)||12 to 16|