Impact of heat stress on calves (part 2)

Inside the calf hutch

Back in the summer heatwave, outside temperature reached well over 30°C in some parts of the UK. In our trial, the temperature reached a maximum of 25°C, but this was still enough to cause some dramatic changes inside calf hutches.

One of the hottest days of the year here was August 8th- when outside temperature only reached slightly over 20°C, the temperature in the hutch was nearly 40°C! Both hutches shown are over 30°C for 4 hours, giving much greater potential exposure to heat stress for the animals. The direct sunlight caused a greenhouse effect in the hutches and the air flow was insufficient to cool them to the outside temperature. By about 19:00, the hutch temperature had decreased to below 20°C as the sun was no longer directly upon it. 

The next graph shows more of the overall picture within the building, but again it shows that during early August, hutch temperatures consistently peaked at well over 35°C- not a temperature which we want to subject any calf to. For farms in the south of England, there is potential for these temperatures to be considerably higher. 

The impact of shade (even for hutches!)

Above, hutch 3 was one which was only exposed to sunlight in the early morning. When compared to the other hutches, it never reaches the same extreme peaks, with only one day getting to 30°C. 

Potential impact

You may well ask, the calves had access to an open straw area, so does it matter if the hutch gets to 40°C? It is important that the area outside the hutch is of a good size and is under shade so that all the calves can escape from the worst of the heat without being exposed to direct sunlight. A good water supply is also crucial.

But yes, it does matter! Even if this is all in place, it is still going to be detrimental if the calf hutch becomes baking hot- it will radiate further heat throughout the shed and mean that even the straw area is warmer than would otherwise be the case. It may not always be possible to arrange things perfectly, but if the hutches can be kept out of the sun (particularly in the middle of the day) then it will be a better environment for the young calves.

Effect on calves

Calves have two main methods to lose heat- one is through panting and sweating, which loses heat through evaporation. The other is by standing up, which maximises the surface area through which they can lose heat to the air. In extreme temperatures, calves can require 20-30% more energy (Drackley, 2011) to help cool down. Our measurements directly showed an increase in activity of the calves on the hottest days. They also require significantly more water. Unfortunately, as the air temperature gets closer to 40°C then the rate of heat loss through the skin decreases as the difference between air temperature and body temperature gets close to 0. Another factor is the prolonged duration of heat stress- each extra hour at a high temperature increases the impact on the calf.

Conclusion

Hutch placement and orientation can make a massive difference to the heat stress placed upon the calf during heatwaves. Besides the obvious risk of dehydration (and potentially death), there is a direct impact on energy requirements and a consequent lack of growth. There will be different considerations throughout the year, but avoiding direct sunlight on the hutch during noon hours will help to improve calf care during future heat waves. When the hutches are fixed and exposed, temporary shade will help to reduce the impact and could improve the welfare of the young calves.

More general advice is to minimize the amount of wet material in the hutches- this will retain heat and exacerbate the situation. Changing bedding more often will help with this. It is also critical to maximise the air flow, so open up the hutches as much as physically possible. Finally, ensure that the calves have access to feed and water at all times so they can try to meet their nutritional needs.

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