By Peter McGill: Ruminant Nutritionist & Dairy Specialist
Published in the Jameson Journal, April 2026
With warmer temperatures on the way over the coming months, it’s worth getting ahead of heat stress before the cows start telling you about it themselves. While a bit of sunshine is good for grass growth and morale, prolonged warm, muggy conditions can quickly become a problem for dairy and beef cattle, especially when kept indoors.
Recognising early signs before performance drops
Cattle are tough and quite happy anywhere between about –5°C and 15°C. Once it gets hotter than that, though, things start to unravel. When cows are heat‑stressed, they behave much as farmers do in a heatwave ‑ they slow down, avoid unnecessary effort, and generally look fed up with life.
Hot cows tend to stand about with their heads down, panting away as if they’ve just been chased by the dog. Oddly, they will often bunch together as well, which makes about as much sense as huddling around a heater in August.
Protecting fertility, yield and growth rates
High temperatures do not just knock milk yield in dairy cows or growth rates in beef cattle; they also upset fertility, affecting sperm quality and embryo survival right when breeding should be straightforward.
Understanding THI: Why humidity changes the whole equation
Humidity is where it really gets uncomfortable, and referring to the Temperature‑Humidity Index (THI) can prove very useful. In the UK, it is often not the heat but the damp air that finishes off cows. When it is warm and muggy, cows can suffer heat stress at much lower temperatures than you would expect. Feed intakes fall, milk drops, growth slows, and immunity takes a hit, with mastitis waiting in the wings. A 10% drop in intake is a big warning sign, although spotting it at grass is not always easy.
Minimising summer performance losses
Dry cows close to calving often get the short straw. Summer calvers are already eating less and potentially losing condition, and heat stress just adds fuel to the fire. Poor energy at calving, lower colostrum yield, and cows struggling to bounce back before bulling are all common consequences.
So, what helps? First and foremost, water – plenty of it, clean and close by
If the trough is a long walk away or slow to refill, they will just do without. And if you are thinking of moving cows in the heat of the day, think again. In hot weather, cows will drink 10–20% more water, part of this is to aid in their own internal cooling system. When a cow pants, air moving over moist respiratory surfaces causes evaporation that absorbs body heat, providing cooling and accounting for about 15% of its total heat loss. This internal cooling method is strongly influenced by humidity.
Maintain energy intake in hot weather
Feeding strategy matters too. When cows eat less, what they do eat needs to pack more punch. Good‑quality forage produces less heat in the rumen, but during periods of low intake, it often pays to feed more nutritionally dense rations, using concentrates or suitable by‑products to maintain energy intake. Feeding more in the evening or overnight, when it is cooler, can really help intakes. Just do not overdo the concentrates, or you will trade heat stress for acidosis.
Ventilation and shed management
Finally, airflow is king. Open sheds up, swap solid doors for gates, trim back hedges, and avoid overcrowding. Fans and sprinklers can be very effective, especially in collecting yards, but they should support good ventilation rather than replace it. Even at grass, shade, and easy access to water can make a big difference.
If the cows look like they are wilting, they probably are. A few simple tweaks can keep them cooler, healthier, and performing better.
We’re here to support you in keeping your cows cool, comfortable and productive this summer.
Please call 01765 689666 for help and advice.
This information featured in the Jameson Journal April 2026 edition – click here to read more.
