Hypovitaminosis A, otherwise known as vitamin A deficiency, puts chickens at an increased risk of infections involving the skin (bumblefoot), oral cavity, eyes, nasal cavity, throat, and lining of the stomach. 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.
The National Research Council (NRC) recommends that chickens receive 3,000 IU/kg of vitamin A in their daily diet.
Vitamin A deficiency 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.