Cows make moisture and heat. This requires ventilation.  
Fresh outdoor air is necessary to keep cows healthy and lower the barn's moisture levels even when it's cold, regardless of the weather.
Good freestall barn ventilation eliminates odors and gases. The barn design, construction, and management must account for the livestock's moisture load for the best results.
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Managing continuous ventilation by hand can be a significant challenge. Especially when cows are housed in freestall barns, loafing sheds, or compost-bedded packs.

Between 20° and 76°F, is great for Holstein cows as long as the humidity is kept in check.
Temperatures below this ideal range are far more tolerable for cows than above. Cows can survive l below 20°F as long as they are kept dry and out of the wind.

Barns that have condensation on stalls or foggy or damp and musty-smelling are underventilated. Increased air exchange is required until these issues are resolved.
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Respiratory issues during the winter result from livestock housed with too little ventilation. The welfare of the cows is much too frequently neglected in favor of the operator's ease and apparent comfort when running a barn. This highlights the need for better solutions and technologies in livestock management.

Automating your freestall or calf barn curtains helps.
Especially if it's designed exclusively for naturally ventilated barns.
That is why Kevin Hoover started building ventilation controls.
Very few controls did a good job of closing only the correct curtains. They didn't know how to respond to the wind. This is a big deal.

Adjusting the barn curtains to have only the windward side closed, allows your barn to be open at far lower temperatures.