Riboflavin deficiency in broiler chickens

Andrew Brooks, Emily Martin

Animal Health Laboratory, University of Guelph, Guelph, ON

 AHL Newsletter 2023;27(1):20.

Lameness and musculoskeletal disorders are common problems in poultry.  In 2022, the AHL diagnosed multiple cases of confirmed or suspected riboflavin deficiency resulting in lameness and limb paralysis in broiler chickens.

In this series of cases, the affected birds ranged from 10 to 20 days of age, and common clinical signs included lameness, paralysis, inward curling of the toes and increased culling.  Of the cases submitted for postmortem examination, the gross lesions were generally nonspecific, but common findings included curled toes (Fig. 1), mild limb rotation, and evidence of wing walking characterized by lesions on the carpi and wing tips.

Histologically, the diagnostic lesions were present in large peripheral nerves such as the sciatic nerve.  In most nerves, there were mild to moderate infiltrates of mononuclear inflammatory cells including lymphocytes and fewer plasma cells (Fig. 2A).  Schwann cells exhibited hypertrophy and hyperplasia with enlargement of the nuclei, and mitotic figures were evident in many affected nerves.  Axon and myelin sheath degeneration was a consistent finding (Fig. 2B).

Riboflavin, a water-soluble B vitamin (Vitamin B₂), is an essential cofactor for many enzymes involved in energy metabolism and cellular growth.  Riboflavin supplementation is required in poultry rations, and deficiency results in chicks that are weak and slow-growing.  Affected chicks are often reluctant to stand or walk, may rest on the hocks, and may walk with the assistance of the wings.  A characteristic presentation is “curled-toe paralysis” where the toes of the lame birds curl inwards.  Other clinical signs may include reduced growth, diarrhea and increased mortality.  When detected early, riboflavin deficiency can be treated effectively with vitamin supplementation.   AHL

Figure 1. Chick affected with “curled-toe paralysis” due to riboflavin Deficiency (photo courtesy of Dr. Anastasia Navy).

Figure 2. Lesions in the peripheral nerves associated with riboflavin deficiency (H&E stain). A. Mononuclear cell infiltrates (arrowhead). B. Schwann cell hyperplasia and hypertrophy, with mitotic figure (arrow), and axon degeneration (arrowhead).

References
1. Classing KC, Kroger DR. Nutritional Diseases. In: Diseases of Poultry, 14th ed. Swayne, DE, ed. Wiley Blackwell, 2020:1270-1271.
2. Shiva Prasad HL. Nutritional diseases. In: Avian Disease Manual, 8th ed. AAAP, and 2019:148-149.