Although the subject of heat stress has been mentioned before, some of the predictable changes in cattle systems in the UK are beginning to bite on animal health and welfare.
The first change is that as cattle become more productive, they process more energy and need to dump more sensible heat to maintain energy balance. The second is that increased production requires increased moisture throughput, with a high yielding dairy cow consuming water in excess of 100 litres per day.
This means a building with 200 dairy cows will have a throughput of more than 20,000 litres of water per day, with at least 16,000 litres of that being excreted back into the system.
The final change is that our cows are increasingly likely to be housed all year round, so livestock building systems have to operate at ambient temperatures above 15c.
One question that has bounced around the livestock building sector for more than ten years is: ‘Is there a requirement for insulated roof sheeting and can the additional cost be justified?’. My response has been that, in terms of hard data, we don’t know.
Our understanding of physiology and relevant meteorology can provide an estimation of the risk from heat stress, in the same way location data and meteorology can give risk guidance for wind loading on structures. We need more data.
Just over 18 months on from the emergence of Covid-19, on farm meetings in the UK have begun again and it was a pleasure to be working in the south-west of England recently.
The focus was how to manage heat stress in dairy cows, and the sun duly shone providing air temperatures above 24c from mid-morning until mid-evening.
My contribution was on using building design to maximise wind driven ventilation without losing control of air speed in the winter months and ensuring there is no restriction of ventilation by stack effect.
The progressive information came from Mark Scott, of Cargill, which like the meeting sponsors Crediton Milling Company is an animal nutrition company, supplying the energy in aspect of our cattle systems.
The question of return on investment from adding costs to our cattle buildings is answered more easily if we know the costs of a system being out of balance. Mark and his colleagues at Cargil have installed temperature and humidity sensors on dairy units around the UK which provide constant monitoring of the thermal humidity index (THI).
This data is useful because there is a temptation to think that our UK air temperatures are seldom stressful, with air temperature data from overseas significantly higher than typical UK summer temperatures in cattle buildings.
In fact, it is more useful to adopt THI as a measure of thermal conditions experienced by cattle than air temperatures because, as air temperatures rise, cattle increasingly rely on dumping moisture from the body into the environment.
Moisture loss by respiration increases two-fold when air temperature increases from 12c to 24c.
This works well in hot, dry climates, but is not so easy in a maritime climate like the UK, with relatively high but normal air humidities. It is hard to dump energy as moisture in a damp atmosphere.
The data collected from 26 farms in the UK can be accessed at www.weatherdatauk.provimi.eu, with the primary observation that from south-west Scotland to south-west England, there are a significant number of days where cattle reproduction and performance is being limited by THI.
Managing heat stress on UK cattle units
Where the number of days per year of THI above 65 is very low, the opportunity for return on investment will also be low. However, the evidence that UK cows are becoming heat stressed is clear.
Managing heat stress can be done at the design stage of buildings and also retrospectively. For example:
- Drainage slopes prevent the accumulation of moisture.
- Sidewall cladding to provide wind driven air movement without losing control of winter air speeds.
- No restriction of the stack effect by the inlets and outlet areas.
- Roof material.
- Roof slopes.
- Water troughs.
The role of the wind is so important in managing ventilation and thereby energy and moisture management in a cattle building, that the location of individual buildings has a critical impact. It is tempting to think our weather is unpredictable, but the facts prove the opposite. It is useful to refer to local meteorological data for a level of predictability about the impact of weather on a building.
Even with drainage and natural ventilation optimised there will still be predictable benefits from helping cows stay cooler. Nutritionists have a role by providing products that change pathways of energy metabolism and can help to reduce body temperatures by 1-2c. Remember, access to clean and cool water helps too.
After that, our systems need more help. Mechanical ventilation is used extensively around the world to cool livestock by increasing air speed across their bodies and increasing the rate of heat loss. As long as the airborne heat and moisture entrained in the fan-driven air leaves the building and is not allowed to accumulate, cow health and welfare will benefit.
The Hot Cows Road Show in July included presentations from Robin Hibberd, of Hydor, on the requirements of and benefits from mechanical ventilation. The main requirement for managing heat stress is to provide large volumes of air across the backs of as many cattle in the building as possible. Some general rules are:
- Locate fans to move air in same direction as predominant wind direction, where possible.
- Locate fans in series to ensure the moving air column does not accumulate inside buildings.
- Locate fans so that air flow passes around the cattle, not above.
- Balance fan types and capacity to available power supply and running costs.
- Persuade the client that the cost of automatic control, probably for temperature and humidity, provides good value.
The addition of mechanical ventilation also provides the possibility of adding water to livestock systems and increasing the rate of energy from a body by evaporation. Spraying of water – or misting – may be particularly valuable in THI hot spots such as collecting yards, but never where ventilation is compromised.
So, I return to the original question: ‘Is there a requirement for insulated roof sheets?’. The current information on THI in UK cattle buildings strongly suggests there is a need, and that return on investment will depend on the scale of current losses.
RIDBA Livestock Consultant