Calves under three weeks of age have a thermal neutral zone (TNZ) between 59 and 78ºF. Below this zone they begin to experience cold stress, and above this zone they experience heat stress. Calves and heifers over three weeks of age begin to experience heat stress at 70ºF.
In the July 2012 issue of the Miner Institute Farm Report, Kimberley Morrill, northern New York dairy specialist with Cornell Cooperative Extension, looks at the impact of heat stress on the calf's energy requirements, immune system function, growth rates and water intake.
She also discusses these heat stress abatement strategies:
Timing of stressful activities (moving, grouping, vaccinating and dehorning).
Fresh and clean feed
Capitalizing on the natural breeze, or creating one with fans.