Cattle genetics have changed substantially over the last 50 years. Over that same period of time, though, cattle housing has seen very little change. The modern dairy cow produces more milk, but does so at a 2.5-fold increase in moisture and energy consumption. And that moisture and energy has to go somewhere. Poorly ventilated buildings can be disastrous to cattle health since they’re not only an uncomfortable environment for cattle, but also hold moisture and heat, creating the perfect environment for bacteria to thrive in. Jamie Robertson of Livestock Management Systems in Scotland explains why cattle building design is important in terms of managing animal health and welfare.
Management of cattle pathogens becomes easier when the behaviour and survivability of those pathogens is understood. Environmental conditions can either favour or restrict population growth. Note that those same conditions have an impact on cattle immune function as well.
The influence of environmental factors in the environment/pathogen/host interface is most easily understood in relation to animal hygiene, Robertson explained.
“Once animals are placed inside a building there is a natural restriction in how an individual can choose to react to the built environment,” he said. “Flight is not an option, so a body has to fight pathogen presence as well as the environmental conditions that support the pathogen in the first place.”
Barn design and its impact on health
Today’s cattle sheds have seen little change over the last 50 years. And while many farmers have upgraded their barns, they’ve often done so by adopting systems that were created in environments very different from their own.
Important factors to consider when evaluating building design include prevention of the accumulation of heat and moisture, proper ventilation to provide fresh air, and means to protect against high winds. But design also plays a role in disease prevention, especially where pathogens are already present.
Where design is going to go wrong is in one or more of five routes, said Robertson, pointing to moisture, fresh air, air speed, temperature and hygiene.
“You take them any way you like, none of them are more important than the other,” said Robertson.
Cattle barns are wet environments. A 200-cow barn can easily process 10,000 to 12,000 liters of water a day, said Robertson. Drinking water is converted into milk, faeces or urine, or expired as moisture. That moisture has to go somewhere, and if it is not removed altogether, it will accumulate inside the barn.
Moisture management is key in the barn, said Robertson. But in order to manage moisture one must first understand where it is coming from. Key considerations include factors like manure management, as well as air quality and removal.
Each cow can put up to 10L of water as moisture into the air every 24 hours during the winter months in the UK. In a 200-cow barn, that two tons of moisture needs to be removed each day. In the summertime, cattle will increase their rate of respiration and dump twice as much moisture into the air around them, said Robertson.
“If moisture accumulates, you’re probably looking at a problem,” he said.
The same can be said of energy. Energy consumed will translate into growth, milk and foetus production, and waste. Cows may also produce as much as 240KW of radiant energy per 200-cow herd, which is enough to power 24 homes, said Robertson.
“Animals need to get rid of this sensible energy,” he explained. “They’re radiators. It’s very easy in winter, especially in Scotland.”
“But come summertime the temperature goes up and they’re still trying to get rid of the same amount of energy, so it’s not so easy,” he continued. “They’re pumping moisture out – respiration – and that has to be dealt with. If it’s not dealt with because the building doesn’t ventilate very well, we’ve now got an accumulation of moisture and an accumulation of heat.”
“What do you think likes heat and moisture?” he asked. “You kind of, by default, have designed an environment that every summer is going to be really nice for gram-negative bacteria and some of the gram-positives.”
Thermal dynamics – or the energetics of a building – are well understood, but little applied to barn design, said Robertson. Design features that influence the thermal dynamics of a cattle barn include:
- Materials used in construction
- Orientation of the building
- Slope of the roof
- Design of the roof
- Roof lights
- Design of side cladding
- Surrounding topography
Furthermore, these design features have a long-term impact on cattle health, said Robertson. If either the cow or the building gains too much energy ambient temperature will rise within the building. This rise in temperature, said Robertson, influences everything from animal behaviour to respiration rates, feed intake and moisture throughput. In fact, the main beneficiaries of increased energy and moisture are the pathogens.
The goal is to create a safe environment that does not cause physiological stress and does not enhance the survivability of pathogens outside of the host. That means managing temperature, fresh air, air speed and hygiene.
For the most part, fresh air is supplied by the wind, which comes from all directions, so it’s crucial to add features that enable wind to pass through, and to remove obstacles that hinder its movement. Moisture accumulation and pathogen survival rates will increase in areas where fresh air movement is reduced, said Robertson.
The rate of thermal loss from the barn is directly related to the thermal conductivity of the materials used in its construction, Robertson explained. For example, metal (tin) roof sheeting, which is often used because of its low cost, negatively impacts moisture management and natural ventilation rates.
The orientation of the building also impacts thermal dynamics in terms of solar gains and wind exposure. Furthermore, roofs with low slope will have increased solar gain. Increased slope, on the other hand, leads to increased capacity for thermal loss through ventilation.
Since wind is the primary driver of ventilation, sidewall design is an important feature to consider in building design, as well. Without cladding, producers have no control over air speed and risk significant energy loss.
Even if farmers have to change cladding size on the side of the building, an investment that could cost them well over €10,000, it’s worth the investment when considering potential losses, said Robertson.
“I know people who spent GBP 6,000 and made the money back in 18 months by the improvement in performance,” he said.
With regards to the roof, the design and location of apertures impact the exhaust of byproducts, and the design of the ridge cap impacts its natural exhaust capability.
“Cement fibre roof sheeting is significantly superior for livestock housing in the UK than a metal roof cladding for a number of reasons, not least that daily energy gain will be less in warmer ambient air conditions,” said Robertson.
What’s more, the colour of roof sheeting has an even greater impact on solar gain with the absorbance of a medium colour being 27 percent higher than a light colour, he said. Even a dirty roof can impact thermal gains.
Ventilation is of little use without fresh air. The target in a barn is to have fresh air move across as much of the building as possible. The main driver of air movement is wind energy.
Fresh air is a biocide that has the capacity to reduce airborne pathogens in the barn, said Robertson. “The more oxygen and fresh air there is in the environment, the less time these things survive outside the host,” he said.
Fresh air access depends on air speed, said Robertson. In order to take advantage of wind, walls need to remain solid to the height of the animal. Above that, walls should be designed using different material.
“If it’s concrete all the way up, it shouldn’t have animals in it at all,” he said. “It should be a tractor shed.”
There is a ballpark figure to calculate the area of air holes needed in a building based on herd size, Robertson explained. “A rapid assessment of the ventilation capacity of a building is based on an outlet area requirement in the ridge of 0.1 m2 per adult cow, and 2–4 times that in the sidewalls,” he said. “It provides a rapid assessment of what the building needs and can be compared with what is actually in front of you.”
“So when you go to choose a cladding to put in the wall, the cladding needs to deliver 20 m2 of opening for a 200-cow herd,” said Robertson. “And that can be achieved in lots of different ways.”
A method for calculating the total area of inlet for adult cattle can be found in AHDB Dairy Housing Guide and the AHDB BRP+ Better Cattle Housing Design, found at: https://ahdb.org.uk/knowledge-library/brp-better-cattle-housing-design.
Where the natural layout of the barn and surrounding buildings does not allow free movement of air, Robertson urges producers to consider the use of fans. Mechanical ventilation can help improve air movement and the removal of energy, moisture and other by-products. It can also help cattle to lose heat when ambient temperature rises.
Before employing mechanical ventilation, though, Robertson notes that it is important to improve natural airflow as much as possible. Ensure entrained, dirty air leaves the area where livestock are housed, and check daily running costs.
The designs in the ADHB booklet have been around for 35 years, said Robertson. “One of the problems that the farmers and vets have is that the builders just keep building them the way they always have done,” he said. “And because we can build barns big enough for 200–300 cattle, we do. But they should be asking the question: How do I get fresh air in the middle of a building that’s 30 meters wide and full of cattle?”
In terms of design, the last factor for consideration is hygiene, especially when it comes to mitigating mastitis and improving udder health. When considering hygiene, Robertson said it’s important to consider how easy it is to clean stalls, bedding, flooring and equipment.
“If you view the different aspects of a cow’s life through a farm, and areas where mastitis or organisms associated with mastitis might be problematic, the big picture, the financial value of getting the main cubicle building working better in terms of environment is that it will benefit not only mastitis but other things as well,” said Robertson in conclusion.
Text: Melanie Epp – Pictures: Jamie Robertson, Livestock Management Systems, Scotland