Introduction
Feed intakes and milk yields during typical summer conditions in temperate regions are maintained at near-normal levels in barns that have good air exchange. During hot, humid weather, however, air velocities at cow level must also be sufficient to enable a cow to dissipate heat fast enough to offset her rate of metabolic heat production. Directing airflow past cows' bodies has been shown to boost cows' capabilities to dissipate heat substantially if adequate air exchange already exists, thereby reducing the number of hours or days during which cows experience heat stress.
Airflow can be directed toward housed cows in different ways. The most common system for dairy operations consists of a naturally ventilated barn with axial-flow fans placed over interior regions of the barn where supplemental cooling of cows is prioritized, such as along feeding areas. In another system - tunnel ventilation - air exchange is achieved by mechanical means and the ventilation rate is primarily based upon achieving airflow through the building at a desired velocity. Reliable information is not available for comparing and contrasting the effectiveness of these two summertime ventilation systems, making it very difficult for producers to make building decisions with confidence.
A study was initiated to enhance our understanding of ventilation's effect on cow performance and to learn more about the application of tunnel ventilation for dairy production. This paper discusses the results of comparing convective conditions (temperature, humidity, and air velocity) at cow level at several locations within representative naturally ventilated barns (w/supplemental cooling fans) and tunnel-ventilated barns.