Heat stress of dairy cows - KRAIBURG Practical Experience
Heat stress of dairy cows - KRAIBURG Practical Experience

Heat stress on cows

The optimal temperature range for dairy cows is between 4° and 16° C
→ rising summer temperatures cause heat stress on cows

Symptoms e. g.:

  • increased standing
  • rapid shallow breathing > 80/min
  • body temperature > 39° C
  • the animals accumulate at better ventilated spots

Problems from heat stress:

  • stress on metabolism → lower feed intake, reduced fertility and lower milk yield
  • more standing → more load on the claws
  • increased risk of lying damage through sweating and softening of the skin

heat stress on cows depending on temperature and humidity

Source: DLG Merkblatt 336

Heat stress starts at 24° C; above 27° C there are significant reductions in yield.

Air temperature and relative humidity must always be evaluated together: 
  • the cow generates not only heat but also water vapour (15 l water per day at -1° C and 30 l per day at 26° C) 
  • the higher the humidity, the more cows react to heat stress, especially the high yield ones

→ humidity should not be over 70%, which means that high air change rates (60 to 100 times per h) are required!

Tips:

  • maximize water availability
  • optimize feeding management → feeding more often and at cooler times of the day
  • supporting ventilation → dissipates heat and humidity:
    o required at air speeds < 1 m/s
    o highest cooling effect at 2.5 m/s air speed; harmless up to 5 m/s
    o rule of thumb for ventilators: per 10 cm diameter 1 m range,
    common sizes: 12 – 15 m range, in twin block: 18 – 20 m
  • water cooling (source: DLG-Merkblatt 336 [explanatory leaflet])
    o Caution: high pressure misting → principle “air cooling”:
    - technically difficult because of fine nozzles
    - per 1° C cooling, relative humidity increases by 5 %!
    o Tip: low pressure atomizing → principle “soak the hide, cool the animals through evaporation”:
    - technically easier, e.g. horticultural irrigation systems are utilizable
    - only at temperatures > 24° C
    - 15 min intervals (3 min water spraying, 12 min for evaporation)
    - 1 l water/m² (and 3 min spraying)

Water cooling only up to 70 % rel. humidity, therefore humidity sensors are important!

Keep in mind with non-insulated stables:
  • Non-insulated roof: → additional heat influx 165 – 990 W per cow possible!
  • Lower temperature difference outside/inside:
    → the air can absorb less water vapour
    → higher air change rates required (in winter, too)

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