Roup, Hypovitaminosis A, Follicular Hypeerkeratosis, Phrynoderma, Squamous Cell Hyperplasia
Vitamin A Deficiency Overview
Vitamin A is made up of three different forms of compounds, which include retinols, beta carotenes, and carotenoids. The National Research Council (NRC) recommends that chickens receive 3,000 IU/kg of vitamin A in their daily diet.
Vitamin A is essential for vision , immune response, bone growth, reproduction, the maintenance of the surface linings of the eyes, epithelial cell growth and repair, and the epithelial integrity of the respiratory, urinary, and intestinal tracts.
Vitamin A deficiency (VAD) occurs in malnourished and chronically sick chickens that are not provided any access to fresh green forage or other foods containing high levels of vitamin A. It causes abnormal vision adaptation to darkness, dry skin, increased nail breakage, and decreased resistance to infections. This is because a diet deficient in vitamin A causes disturbances to the protective mucus lining surrounding the outer layers of the chicken's esophagus (throat), oropharynx (oral cavity), paraocular glands (involving the eyes), sinuses (nasal cavity), proventriculus (stomach), and bursa of Fabricius. VAD can be caused by:
- The chicken is not eating as much as they should be.
- The commercial poultry feed purchased is stale (often associated with prolonged storage by the feed store or by the feed purchaser). In one study, vitamin A was reduced to around 2% of the starting value when it was stored under high temperatures and high humidity conditions over a period of 3 months, compared to 88% under conditions of low temperature and low humidity. The stability of vitamin A in the feed depends upon the formulation used and the methods of protection employed by the feed manufacturer.
- Chickens have no access to fresh forage, which contains the highest levels of vitamin A.
- The chicken has an underlying condition that is causing an impairment in vitamin A absorption or storage.
- Poor conversion of carotene to active vitamin A
- Chickens are receiving too much antagonistic (meaning, dietary excess of one vitamin can diminish uptake and availability of another, despite adequate dietary intake) vitamins and minerals that are diminishing uptake of vitamin A in chickens, such as: Vitamin C, Vitamin B3, and Iron (Fe).
Research conducted by the Department of Animal Science at Shandong Agricultural University in Shandong, China that was published in 2015 showed that vitamin A deficiency suppressed the immunity of the airway in young chicks, leaving them more susceptible to infections involving the respiratory tract.