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Curly Toe Paralysis

Other Names: Hypovitaminosis B2, Riboflavin Deficiency

Curly toe paralysis is caused by riboflavin (vitamin B2) deficiency in young chicks. It is one of the most characteristic signs associated with the vitamin deficiency, resulting in the curling of the chicks toes. The condition nervous system related due to peripheral nerve damage, related to degeneration of the sciatic nerves (the nerves along the back of the chick's leg to the foot). The damage can be reversed if treated quickly, however in longstanding cases where treatment is delayed the condition will become permanent.

Curly toe paralysis occurs in chicks fed outdated or improperly stored starter feed, or who are bred from parents with a riboflavin-deficient diet. Chicks that are fed a riboflavin-deficient diet will begin to show signs at about 8 to 14 days following hatch. They will slowly develop progressive symmetrical paresis starting with initial signs of reduced growth rate (despite a good appetite), weakness and sometimes diarrhea. 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. The condition is still treatable however, as the chick's peripheral nerves are able to rapidly regenerate once riboflavin levels are restored.

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 the 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), however the recommended riboflavin levels based on research conducted by DSM Nutrition is as follows:

Age/Life Stage	mg/kg
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

Dietary Food Sources of Riboflavin

Riboflavin is one of the vitamins most likely to be deficient in poultry feeds. Only a few feed ingredients that are used in poultry feeds that contain enough riboflavin to contribute to the requirements for growth and reproduction. Fermentation significantly increases the proportions of riboflavin present in the free form.

Clinical Signs

Toes curled inward like a fist (both when walking and resting)

Weakness

Normal appetite

Diarrhea

Rough and dry skin

Diagnosis

History
Clinical signs
Physical exam
Diet evaluation

Treatment

Name	Summary
Supportive care	Isolate the bird from the flock and place in a safe, comfortable, warm location (your own chick "intensive care unit") with easy access to water and food.
Vitamin B2 (Riboflavin)	Administered IM (1-3 mg/kg q7d) or orally (1-2 mg/kg q24h)	B Speers
Feed management	Replace current feed with a new bag of quality chick starter feed.
Corrective shoe	Splinting the toes at the first sign of deviation. Involves taping the affected toes into a normal position for 2-3 days. This can be accomplished by making a corrective shoe, constructed from a piece of firm material such as thin cardboard or radiographic film. The shoe should be made to properly fit the foot of the affected individual with a notch in the shoe into which each toenail is placed in the shoe and each digit is taped into a normal position using very thin strips of masking tape. Should be monitored closely as deformities can be caused by leaving bandages or splints on too long.

Support

Prevention

Ensure any adult chickens intended for breeding are receiving enough riboflavin in their diet (10-16 mg/kg).
Feed newly hatched chicks a fresh bag of starter chicken feed (not feed that has been stored for longer than 2 months), with additional riboflavin food sources during the two weeks of life.
During warm weather, provide supplemental sources of riboflavin.
Store feed in a sealed plastic container located away from direct sunlight.

Prognosis

Good if treated promptly

Scientific References

Rebecca Duerr, DVM MPVM. Splinting Avian Fractures International Bird Rescue Research Center (2020)
UC Davis California Animal Health and Food Safety Laboratory System. CAHFS Connection Newsletter August 2018 Issue (2018)
DSM in Animal Nutrition & Health. Riboflavin DSM (2017)
DSM in Animal Nutrition & Health. DSM Vitamin Supplementation Guidelines 2011 DSM (2017)
Z Cal, P Blumbergs, J Finnie, J Manavis, P Thompson.. Selective Vulnerability of Peripheral Nerves in Avian Riboflavin Deficiency Demyelinating Polyneuropathy Veterinary Pathology (2009)
Z. CAI, J. FINNIE, P. BLUMBERG Avian Riboflavin Deficiency: An Acquired Tomaculous Neuropathy. Veterinary Pathology (2006)
White HB 3rd. Sudden death of chicken embryos with hereditary riboflavin deficiency Journal of Nutrition (1996)
Abrams VA, Han CC, White HB 3rd. Riboflavin-deficient chicken embryos: hypoglycemia without dicarboxylic aciduria Comp Biochem Physiol B Biochem Mol Biol (1995)
National Academy. Nutrient Requirements of Poultry Washington, D.C. (1994)
W. Johnson, R. Storts. Peripheral Neuropathy Associated with Dietary Riboflavin Deficiency in the Chicken Veterinary Pathology (1988)
Summers, J. D., et al. Influence of vitamin deficiency and level of dietary protein on the incidence of leg problems in broiler chicks Poultry science (1984)
Gries CL, Scott ML. The pathology of thiamin, riboflavin, pantothenic acid and niacin deficiencies in the chick.. J Nutr (1972)

Geographical Distribution

Age Range

Newly hatched chicks are most susceptible to developing curly toes

Risk Factors

Feeding adult chickens (intended for breeding) layer feed. Layer feed does not provide the nutrients needed to prevent deficiencies in hatches chicks.
Stale feed - Feeding chicks outdated, improperly stored, low quality, or nutrient-deficient starter feed
Feeding a corn-soybean meal based diet without providing supplemental riboflavin
Warm climates - Environmental temperatures also have an impact on riboflavin requirements, and more is required for chickens raised in a tropical environment or exposed to chronic heat stress.
Genetics - more modern strains of chicks that have been selectively bred for high egg production and "meat quality" (broilers)