Natural light is a proven benefit for all Livestock

Fabric covered buildings from NLFS allow natural light in while providing considerable protection against UV rays.

Studies have been done by dairy scientists at Michigan State University (Peters et al., 1978), the University of Maryland (Miller et al., 2000), and the University of Illinois (Dahl et al., 2000) that conclusively show how an increase in the amount of light that a dairy cow is exposed to increases her milk production almost immediately.

http://www.associatedcontent.com/article/1271329/extra_light_can_naturally_increase.html?cat=15

This is true for other species of animal that are used around the world for dairy production, such as sheep and goats.