Ventilation, Temperature, and Relative Humidity

Source: National Farm Animal Care Council Code of Practice for the care and handling of farm animals – Dairy Cattle, Section 2.4

Ventilation

Good ventilation, whether natural or mechanical, brings in fresh air and effectively removes dust, airborne pathogens, gases, and excess heat and humidity (6). Dust and ammonia irritate animals’ eyes and respiratory tracts and can make cattle more susceptible to respiratory infections. However, definitive thresholds for cattle have not been established, including for ammonia (6).

The risk of pneumonia and other calf diseases can be dramatically reduced through good ventilation (without drafts) and the provision of adequate air space (i.e., at least 6 m³ [212 ft³] per calf up to 6 weeks of age and 10 m³ [353 ft³] per calf up to 12 weeks of age) (22). One of the biggest pneumonia risks for young calves is sharing airspace with older cattle (23).

Temperature and Relative Humidity

Mature dairy cattle are generally able to tolerate low temperatures better than high temperatures (6). When the ambient temperature is above the thermoneutral zone, heat stress occurs because heat load (accumulated both metabolically and from the environment) is higher than the animal’s ability to dissipate heat (6). The specific ambient conditions (temperature, humidity) that lead to heat stress vary based on the cow’s previous temperature acclimation as well as level of milk production, breed, and other factors (6). High-producing cows are most susceptible to heat stress due to the increased energy demands of milk production (6).

The thermoneutral zone for young calves (up to 3 weeks of age) is 15–25°C (6). Particular attention should be paid to temperatures inside calf hutches, which can far exceed ambient temperatures on hot days (6).

RECOMMENDED PRACTICES

1. consider how many days above or below ideal temperatures for cattle are experienced in a typical year when choosing an appropriate cooling system
2. monitor cattle routinely for behavioural responses to heat stress, which occur prior to dips in productivity (e.g., increased standing time with shorter lying bouts, panting or increased respiration rate, competition for cooling resources, increased drinking bouts) (6)
3. ensure good ventilation in milking parlour holding pens
4. limit reliance on misters and sprayers in high humidity regions (6)
5. always evaluate air quality, temperature, and speed at cattle level (resting and standing)
6. if ammonia is ever readily detected by smell, test actual concentrations and take remedial action to ensure it stays below 5–10 ppm
7. remove manure and soiled bedding from facilities frequently
8. avoid housing calves in the same air space as older cattle to minimize the occurrence of pneumonia (22)
9. house calves in well ventilated (but draft free) buildings or in hutches that provide ample fresh air through doors, windows, and top vents
10. avoid situating calf pens in areas of the barn that tend to be cooler (these conditions are associated with higher disease risk for calves) (24)
11. avoid exposing cattle to sudden extremes of temperature
12. design and locate enclosures to take advantage of prevailing summer winds and reduce the amount of solar radiation that enters the barn (barns with an east-west orientation allow less heat from the sun to enter) (6)
13. ensure appropriate seasonal orientation of hutches (i.e., winter: with the opening facing south to maximize sun exposure; summer: in shaded areas or with the opening facing north to maximize shade)

When facing cold stress:

14. gradually increase energy intake of calves and heifers in anticipation of cold weather to ensure that growth and weight gain are maintained during periods of cold temperatures
15. protect cattle from wind and moisture
16. protect cattle, and especially young calves, from drafts (e.g., build temporary walls/shelters in open-sided barns in the winter)
17. ensure that the relative humidity inside a housing facility does not exceed 75%
18. provide calves with clean and dry calf coats in addition to deep bedding (6)

When facing heat stress:

19. avoid unnecessary procedures or other stressors during the hottest times of the day
20. provide cattle with access to shaded areas (6)
21. increase air flow by opening barn doors and vents fully and adding more fans, especially in areas where cattle are misted/sprinkled (e.g., holding areas) (6)
22. open all vents in hutches or elevate the back of the hutch (by 20 cm [8 in], as a guide) (6)
23. sprinkle or mist the backs of cattle when they are feeding or otherwise away from resting areas (wetting cattle in resting areas may increase mastitis risk) (6)
24. modify hutches to have a reflective covering in the summer (6)
25. choose sidewall heights and overhangs of the roof to reduce sun exposure to stalls, walkways, and bedded packs
26. use shade cloth when and where needed to minimize the effects of sunlight that enters the barn.