Optimising calf environments for health, performance and efficiency
Getting the calf environment right is one of the most immediate and cost-effective ways to both improve performance and lower emissions on UK dairy farms.
At a UK Dairy Carbon Network (UK-DCN) event on 11 March 2026 at Two Pools Farm, South Gloucestershire, livestock housing consultant Jamie Robertson outlined how to assess and improve calf environments for better health, performance and efficiency.
Successful calf rearing is built on understanding five core environmental factors: fresh air; moisture; airspeed; temperature; and hygiene.
“People often assume that a lower stocking density or a newer building means fewer problems,” said Jamie. “But the same stocking density can deliver quite different outcomes depending on the environment.
Calves are physiologically stressed with naïve immune systems at birth. If the environment adds further stress, disease risk rises. High-quality colostrum is essential, but so is getting the environment right.”
Fresh air
Fresh air flowing through the calf shed acts as both a transport system and natural biocide, removing moisture and gases while reducing pathogen survival.
However, airflow is often restricted by poor ventilation. “A survey of 92 calf sheds found 40% had seriously inadequate ventilation, with only 10% completely competent,” said Jamie.
Outdoors, pneumonia-causing viruses survive for around four to five minutes when exposed to fresh air and sunlight. Indoors, with sub-optimal ventilation, this increases to 40–50 minutes, significantly raising infection risk.
Ammonia levels above 25 parts per million (ppm) irritate the airways and increase the calf’s susceptibility to respiratory disease, while dusty bedding can also cause irritation and exposure to mould spores.
“If you can smell ammonia or stale air, ventilation is insufficient,” said Jamie.
Simple checks include observing calf behaviour, looking for condensation or cobwebs, and using smoke pellets to assess airflow.
Moisture, airspeed and temperature
Calves under three-weeks-old have a thermoneutral zone of 10-15˚C – the temperature range withing which the calf does not have to expend energy to maintain normal body temperature. Older calves are comfortable between 6-10˚C.
Lower critical temperature (LCT) and upper critical temperature (UCT) are the temperatures at which the calf must expend energy to either keep warm or cool down.
However, the temperature a calf experiences is influenced by airspeed, humidity and ground conditions. “Five degrees Celsius and damp feels colder than five degrees Celsius and dry,” said Jamie. “Moisture also provides the ideal conditions for harmful microorganisms to survive longer in the environment, outside the host.”
Jamie advised that airspeed is the first thing farmers should look to control, with moisture second, and temperature third.
“Airspeed is the number one environmental factor for immune system suppression and changing the efficiency of digestion,” said Jamie.
Air speeds at calf height should be around 0.25m/sec – anything higher is considered a draught. Airspeed can be measured using an anemometer, with the aim of eliminating draughts without restricting overall airflow.
Calf temperature should be managed primarily through nutrition, alongside a winter-feeding regime, supported by deep, dry bedding for nesting, and appropriate use of calf jackets where required.
Jamie also shared insight from a winter study conducted on a commercial Aberdeenshire herd, where well-managed calves achieved up to 900g/day growth in their first week of life.
Ventilation design
“Wind is the main driver of ventilation,” said Jamie. “Wherever you are in the UK, about 60% of the prevailing wind comes from the west/south-west.”
Effective ventilation relies on balancing inlets and outlets. Outlet area should be at least 0.04m2 per calf, with inlet area 0.08m2 per calf (0.04m2 on each sidewall), positioned at least 1.5m lower than the outlet to promote upward airflow.
For 100 calves, this equates to 4m2 of outlet – around a 0.2m continuous ridge gap in a 20m building. For 80 calves, 3.2m2 requires a gap of about 0.16m.
A covered open ridge is the most effective outlet. Adding an upstand on either side reduces rain ingress while increasing wind speed over the ridge, creating negative pressure that draws stale air out of the building centre.
Sidewall design is equally important. Ventilated cladding like Yorkshire boarding allows consistent air entry while limiting rain penetration. Any restriction to inlet space reduces clean air delivery.
Where buildings are sheltered or during still conditions, natural ventilation may be insufficient. Farmers should consider positive pressure tube ventilation (PPTV) systems, which can provide consistent airflow.
These systems should deliver 35–105m3/hour air per calf and achieve at least four air changes per hour. Crucially, the minimum rate must be maintained at all times.
Air should be delivered evenly to calf lying areas at less than 0.25m/sec, with airflow from PPTV systems stopping around 1.2m height to avoid draughts.
Poorly designed systems, or fans without tubes, often result in uneven airflow, allowing stale air to accumulate beyond 6-10m from the fan.
“Ventilation only works when it’s consistent,” he said. “It is quite common for farms to use a PPTV system but to turn it off ‘in cold weather’ to protect the calves. If you turn the system off, not only are the calves still cold, but they now have no fresh air and are in a damp environment.
The aim is to deliver clean air at all times, regardless of weather conditions.”
Through the UK-DCN, this approach highlights how simple, practical changes to calf housing can deliver measurable gains in performance, health and emissions.