Beat the Heat, Part Two
AUTHOR: Colin Mason
BVM&S BSc Cert CHP MRCVS
Heat stress is no longer an occasional summer problem for UK dairy herds, as global warming has increased, so has the temperature of UK summers. In this blog, the second in a three-part series, Ruminant Revival vet-consultant Colin Mason addresses the science of heat stress and the practicalities of managing it effectively. He focuses on what farmers can do to protect the health and welfare of their housed cattle.
In part one of this series, we examined the environmental and physiological factors that make heat stress an increasingly significant challenge for dairy herds. Now the question becomes: what can we actually do about it?
Start earlier than you think
You may think heat is just about temperature, but taking humidity into account is really important. The more humid it is, the hotter it feels, and cows will feel it much more than humans do. The problem is that many farmers wait for those high-summer days when cows are visibly struggling before taking action. Cows can start to feel the effects of heat stress at temperatures as low as 14°C when humidity is high enough, and by the time they are visibly panting, damage to welfare and productivity is already accumulating. A useful practical guide is the hoodie rule: when April becomes warm enough that a human is thinking about removing a hoodie, it is time to start thinking seriously about heat stress in your herd.
Monitoring THI in your shed
Knowing the THI (Temperature Humidity Index) outside is a start, but conditions inside a large dairy shed can vary dramatically from one end to the other. A single monitor by the door will not tell you what is happening where your cows are actually standing, and the more cows there are in a small enclosed space, the hotter it will get. In hot weather, cows will often congregate in the darkest corners of the shed, equating shade with coolness even when those areas may not be at a lower temperature.
Cattle naturally generate a lot of heat, so when they bunch together, the temperature can quickly climb. Ensuring uniform light levels throughout the building, combined with effective ventilation in all areas, discourages clustering and keeps cows more evenly distributed across the shed.
Monitoring the THI in your shed in multiple locations – particularly areas where the cattle congregate – is the best way to get a true picture of what your herd is experiencing. Shed-mounted monitors or the online resource THI-LIVE are both practical options for tracking conditions throughout the spring and summer.
Ventilation and the building
For naturally ventilated buildings, the key is to be aware of ‘the stack effect’. This occurs when cool air enters through the sides of the shed, is warmed by the cattle, rises, and exits through the roof vents. If there isn’t adequate ventilation, hot air stagnates around and above your cows.
Where natural ventilation is insufficient, mechanical ventilation through fans can make a substantial difference to performance and welfare. The electricity costs involved are typically outweighed by the gains in reduced disease and maintained production. Farms generating their own energy, for example, solar panels, are particularly well-placed here.
Water: The non-negotiable
A fun fact that’s not well known outside the farming community is that dairy cows consume on average, 100 litres of water per day and their water consumption can easily double in hot weather. Trough space should be at least 10 centimetres per cow, with fast refill rates. Water must be clean and fresh, and troughs must be well-positioned so they do not create bottlenecks. Check your water capacity before summer arrives – it is one of the lowest-cost, highest-impact interventions available.
Feed management
Along with drinking a lot, cattle eat a lot. Cows have the second most sensitive sense of smell in the animal kingdom, behind only elephants. Because feed left out in hot conditions will rapidly ferment or compost, cows will refuse to eat it.
The best solution is to feed smaller amounts to your herd more frequently, keep rations fresh, and remove refused feed promptly rather than letting it deteriorate. Dry matter intake can fall by 10–30% in heat-stressed animals, and every feeding decision should aim to limit that loss. Cows will also naturally increase feed intake during cooler overnight periods, so ensuring fresh feed is available during those windows will help maintain intake.
Cooling at milking
Misters in the parlour or holding area provide effective evaporative cooling at a critical time of day. Fans remain the more widely adopted solution in the UK, but misting systems are likely to become increasingly relevant as temperatures rise, and the two can be used in combination.
For more information about getting to grips with heat stress, contact info@ruminantrevival.co.uk and look out for the third blog in Colin’s series, where he’ll explore how to deal with heat stress in the herd outside.
