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

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

Source: DLG Merkblatt 336

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

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!

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!

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)