If left unmanaged, heat stress can have extremely detrimental effects on livestock. It impacts health and well-being, reduces performance and food intake, and can also cause fertility issues.
Below, building specialist Jamie Robertson explains practical steps farmers can take to alleviate heat stress and highlights some of the changes a Devon dairy farm could make to keep stress to a minimum.
How does heat stress occur?
The onset of heat stress is based on more than temperature, and is rather the result of temperature and humidity.
In hot weather conditions, Robertson says it’s important to use the temperature humidity index to more accurately understand the heat felt by livestock.
How to reduce heat stress?
There are a number of practical steps farmers can take to ensure ventilation is effective and reduce the risk of heat stress in cattle:
- Review building design to maximize natural ventilation – consider efficiency of inlets and outlets
- Provide good access to drinking water
- Avoid/correct all potential causes of overstocking
- Maximize moisture management – specifically examine soils and drainage to minimize moisture issues
- Consider the impact of diet – a balanced diet can significantly lower body temperature in cows
- Paint skylights, especially on south-facing roofs, and keep roofs clean – clean roofing materials absorb less solar energy
- Avoid tin roofs whenever possible. These increase the energy gain under the roof
- Consider fans for cooling and misting in well-ventilated, high-risk spaces
Where fans are appropriate, Robertson says there are a few basics to master. These include installing in the direction of the prevailing wind and ensuring that the air circulates around the cattle rather than over their heads.
How do I know if there is a problem?
Cows exhibit physical symptoms of heat stress, including panting, lethargy and reduced feed consumption.
A Quick Ventilation Assessment is a quick way to get a rough overview of the ventilation efficiency in an existing building.
Assessments should be based on the following:
- Exit area in the ridge = approx. 0.1 m² of cow
- Minimum entry area in each side wall = same area as exit area
- Optimal entry area in each side wall = double the exit area
Heat Mitigation in Action: Case Study – Jim Kirk, Heanton Barton Farm
At a recent dairy farm strategy event organized by AHDB and dairy farmer Jim Kirk, building specialist Jamie Robertson carried out an assessment of buildings at Heanton Barton Farm, near Okehampton in Devon.
Below are Robertson’s six key findings and recommendations for minimizing the risk of heat stress on the 600-head dairy farm.
- Distant dry house
Design: Building in A of 32x16m, with 60 cubicles and a lean-to for 40 cows.
Evaluation: A quick ventilation assessment showed that the building has less than a quarter of the required output. This is likely to cause heat stress during the summer months.
Recommendations: The priority action must be concentrated on the ridge layers, which provide less than 25% of the necessary outlet. The optimum action would be to remove all ridge fittings and attach a covered open ridge with a total gap of 200mm along the length of the shed, to give 6.4m² of output.
- Dry cow / calving barn
Design: 10-year-old building with a 50x8m monopitch.
Evaluation: Ventilation was not considered a problem, although cows prefer the southwestern end of the monoplot where there is probably more fresh air and air movement for a greater part of the month. year.
Recommendations: No action required.
- Heifer/calf shed
Design: Building in A of 55×32.5m. This is a new building with 140 cabins.
Evaluation: A quick ventilation assessment showed that the building has almost 80% of the required output. The sidewalls are excellent for an exposed site, but the depth of timber spacing between the two rows of Yorkshire panels could impact cooling and air velocity during the summer months.
Recommendations: Measure the gaps at the ridge to provide a more accurate figure for the ridge exit. Paint the skylights on the south side of the building to minimize solar gain during the summer months.
Remember to open the cladding on the side by adding another 25 mm tanned batten between the two rows of boards. This would double the entrance area without causing problems with water and wind entering the building during the winter months.
- Delivery of fresh calves
Design: Building in A of 72x 32.5m. This is a new building with 240 cabins.
Evaluation: The building has approximately 75% of the required outlet, according to the rapid assessment of ventilation. This hangar also has side walls, but this building is well protected from prevailing winds as it is built deep into a hillside, so natural cooling will be limited.
Recommendations: Again, it is worth accurately measuring the dimensions of the ridge and painting the dormers on the south side of the building.
Once natural ventilation is maximized, consider the possibility of fan cooling. Two rows of four fans would be ideal, but it is important to consider capital and running costs.
- Main shed
Design: This is an old building located next to the lounge and pick up yard. It is 20 bays long, with space for 350 cows.
Evaluation: This building is sheltered from the wind due to its position between other buildings. The aim should be to extract as much ventilated air as possible from the ridges.
Seventeen spans have crown ridge sheets, which will give less than 25% of the required output. Additionally, the eight spans at the end of the hangar will likely only have 10% of the required outlet. Heat stress is very likely to occur in this building.
Recommendations: Better ridge measurements would be beneficial. Measure the gap between the upper roof sheets and between the two upper purlins. This information will allow an appropriate cost estimate for a crest refurbishment. This improvement could lead to an increase in yield and fertility.
As with other buildings, fan cooling could also improve heat stress management.
- calf building
Design: A fairly well-designed new building with two-stage housing consisting of initial paired enclosures followed by group enclosures.
Evaluation: There is a curtain on the windward side of the shed, which is excellent for ventilation.
There is good drainage everywhere, but the paired enclosures are difficult to clean effectively. This could present a moisture challenge and other health issues.
The top hat ridge has also been identified as non-productive because there is positive pressure in the ridge space more than 90% of the time.
Recommendations: All calf houses of this type of design will benefit from positive pressure tube ventilation. This draws clean air through an external fan at the end of a long tube and is then blown down and through a series of holes through the calf shed. A single tube system in this building would cost around £2,000. Return on investment can be estimated by looking at current drug use.
There are a lot of good design details on this unit, but also a lot of potential to reduce the risk of heat stress. However, ventilation systems should only be considered once all possibilities for natural ventilation have been maximised.
Based on Mr. Robertson’s recommendations, Mr. Kirk has already made changes to the buildings and has future changes in the works.
- In the main barn (photo 5), the bottom of the side walls have been cleared to promote air circulation between the wall and the side cladding.
- Modifications will be made to correct the ridge problem in the calf building.
- As with the main hangar, it is planned to flare the bottom of the side walls on all hangars. It only costs time and can have a big impact.
- The long-term ambition is to build a new dry barn. The design will be based on Mr. Robertson’s recommendations to maximize natural ventilation.