Going Green with NATURAL VENTILATION…

Proper ventilation is needed to provide a healthy and productive environment for livestock and farm workers.  A well designed ventilation system provides an adequate amount of fresh air to supply oxygen, remove excess moisture, and control temperature.  Exhaust mechanical ventilation systems use fans to generate a pressure difference across the walls of an animal building.  Fresh air enters the building through well-distributed inlets and the stale moisture laden air exits through the fans. In contrast, natural ventilation uses local wind and temperature differences between the inside and outside of the building to move air through the structure.  Fans are not used.  Instead the quantity of airflow is determined by the size and placement of openings, roof slope, and orientation of the building with respect to prevailing wind direction.  The pressure differences that drive the exchange of air are from the wind speed and the temperature difference between the inside and outside of the building.  The pressure differences induced by temperature difference, is called the chimney effect.

NOTE:  Dairy cows do not require precise temperature control and can adapt to wide changes in temperature.  As a result, natural ventilation is generally the preferred choice for dairy cow facilities.   

Excerpts from Design and Management of Natural Ventilation Systems (2000)

John P. Chastain, Ph.D., Department of Agricultural and Biological Engineering - Clemson University

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CONSIDERATIONS WITH HEAT STRESS

          A major factor in maintaining optimum milk production and animal health during the summer is to reduce heat stress.  Heat stress occurs when a cow's heat load is higher than her ability to lose the heat.  Mild heat stress can begin when temperatures reach the mid 70º Fahrenheit range and the humidity is in the mid 70's or higher.  The temperature and humidity generate a great deal of environ-mental heat that, when added to the cow's own body heat, creates a heat over load.  In order to get rid of the excess environmental heat, a cow must have access to shade, air movement, and fresh drinking water. Dairy producers know that heat stress not only affects the physical warmth of the livestock, but the loss of milk production, reproduction, and cows along with increased energy bills.

          In order to decrease body heat production, the animal will also reduce feed intake. A reduction in dry matter feed intake begins when daily temperatures exceed 75º F.  University of Missouri research trials showed a dry matter intake drop of 18 percent when temperatures change from 69º to 85º F. Heat stress not only caused reduced feed consumption and milk production but also was responsible for lack of heat detection, decreased fertility, early embryonic death,  lower calf weights and dead cows.

Excerpts from Illini DairyNet Papers 08/05/1998

David B. Fischer