Mechanical ventilation systems rely on controlled inlets and outlets to exchange air in the barn, with a goal of providing a minimum of four to eight air changes per hour (ACH) in winter and 40 to 60 ACH in summer. These mechanical ventilation systems are categorized as positive-, negative- or neutral-pressure systems, with the main differences being how fans are used to bring air into or out of the barn for ventilation purposes.

Failure to permit cows to rest when they want to, for as long as they need to, has a negative impact on their ability to produce milk, become pregnant, stay healthy and remain in the herd.