Ventilation, Temperature, and Humidity


Source: National Farm Animal Care Council Code of Practice for the care and handling of farm animals – Dairy Cattle, Section 1.3


Excessive ammonia levels can pose a health threat to both animal handlers and cattle. Proper ventilation is needed to remove ammonia from livestock buildings. While there are no guidelines related to acceptable levels of ammonia exposure for livestock, the National Institute for Occupational Safety and Health recommends a short-term exposure limit of 35 ppm and a time-weighted average concentration (for up to a 10-hour workday during a 40-hour work week) of 25 ppm for humans (16). All measures should be taken to keep ammonia levels within acceptable human health guidelines. There are several detection methods for ammonia, including litmus paper, detection tubes and electronic devices (1).

Temperature and humidity

Mature dairy cattle are generally able to tolerate low temperatures (down to -37ºC) better than high temperatures (>25ºC) (19). Heat stress is recognized as a major cause of production losses, and specific recommendations to address the issue continue to be developed. Lactating dairy cattle are more sensitive to heat, particularly high producing animals, since considerable metabolic heat is generated during lactation (6). Humidity levels and ventilation affect an animal’s ability to cope with heat stress.

Cows are at risk of heat stress when temperature and humidity exceed a THI, (temperature humidity index) of 72 (17) (see Appendix B – Temperature-Humidity Index Table for more detail). When the THI exceeds 72, additional management is required to keep cows cool. Signs of heat stress include:

  • reduced feed intake
  • increased water intake
  • changed metabolic rate and maintenance requirements
  • increased evaporated water loss
  • increased respiration rate
  • increased body temperature (4).

While dairy cattle can tolerate colder temperatures if acclimatized, calves have a greater vulnerability in cold temperatures.

Animals that are acclimatized to a particular temperature range will face challenges if suddenly required to adjust to extremes of temperature outside of that zone of comfort (i.e., hot to cold or cold to hot).


  1. maintain adequate air quality and ventilation at all times (ammonia levels < 25ppm). Ventilation systems should be capable of keeping the barn dry, removing stale air and strong odors, bringing in fresh air without drafts, and removing excess heat and moisture
  2. remove manure from livestock buildings frequently
  3. avoid exposing dairy cattle to sudden extremes of temperature wherever possible
  4. strive to avoid conditions of heat stress.

When facing cold stress:

  1. allow for increased feed energy intake during cold winter months
  2. protect cows from wind and moisture during winter months
  3. ensure that the relative humidity inside a housing facility does not exceed 75%.

When facing heat stress (THI exceeds 72):

  1. provide shade as the first step in any cooling system
  2. consider average temperature and relative humidity in deciding upon an appropriate cooling system (5)
  3. use evaporative cooling if environmental temperatures are near or above normal cow body temperature for a significant portion of the summer (5)
  4. use a combination of evaporative cooling, tunnel ventilation and feedline soaking for high temperature/high humidity conditions. Do not depend on evaporative cooling alone, except in very arid environments (5)
  5. keep milking parlors, holding pens and housing areas cool during hot summer periods (21).