Below is a link to an interesting article highlighting the benefits of trees in farming. Agroforestry is an interesting topic and something that is carried out more commonly on the continent, but has big potential for the future of UK agriculture and forestry sectors alike.
By creating a managed woodland space on farmland it can provide shelter for the animals, especially birds, to encourage them to roam further. Planting shrubs can also help to provide another level of protection from elements such as the wind and this will help keep the animals warmer. It is also another area that they can explore.
For best results in knowing what trees to plant have a look at what is already gorwing well in the surroundings. By doing this you can identify the which trees grow best in the local climate and soil type of the area.
The trees and shrubs should be planted relatively close to the animals as this will encourage them to move away from their sheds whilst giving them the sense of feeling of protected.
For more information and a good read on the subject the article can be found on Farmers Weekly