The remainder is often obtained through food. Milk, for example, if fortified with vitamin D because children drink it and that keeps them healthy. Chicken eggs also provide vitamin D and since the nutrition fad has swung away from linking eggs to heart attacks it may be possible to give those affordable protein sources a vitamin boost.
Specific wavelengths in the UV spectrum help our skin to form vitamin D and a team had the idea to do that for chickens as well. First, they created proof of concept by illuminating the legs of chickens with UV light under ideal conditions. One chicken per lamp. With that achieved, they moved to real world conditions, using two chicken farms. Comparisons were made between two different chicken breeds, assorted lamps and different durations of light exposure per day.
Humans can't see UV light but chickens can so the scientists continuously analyzed the vitamin D content of the newly laid eggs during the trial period and investigated the impact the additional light had on the animals. Light influences behavior and laying activity.
Using video recordings and also inspecting the chickens' plumage for injuries by other chickens, they were able to assess their potential for activity and aggression.
There were no issues. After only three weeks of UV light exposure for six hours per day, the vitamin D content of the eggs increased three to four-fold. This value did not increase any further in the following weeks. The additional UV light did not cause any obvious problems for the hens. They neither avoided the area around the lamps, nor did they act any differently. As a result, the researchers conclude that their method also works under practical conditions and that this could represent an important step towards supplying the population with vitamin D.
And it could be rolled into wider testing now.