16 June 2025
A Welsh study has flagged up the value of scanning calves’ lungs for respiratory disease damage as two-thirds of the animals with lesions had never had any clinical symptoms.
Respiratory disease is a major cause of mortality and morbidity in dairy calves and has a major impact on welfare and growth rates and also their future performance as lactating cows.
Two hundred and fifty-six calves on eight dairy farms were scanned using thoracic ultrasound (TUS) at between six and 10 weeks old as part of a Farming Connect-funded project.
The scanning, which uses high-frequency sound waves to capture live images of internal body organs, revealed abnormal lung lesion scores in 54 calves and these animals were scanned again four weeks later.
Farm records showed that only 33.3% of those 54 had previously shown signs of respiratory disease such as a cough, nasal discharge, drooping ears and depression, and then been treated with an antimicrobial and an anti-inflammatory.
The others hadn’t been treated which suggests their symptoms were sub-clinical, says Bedwyr Roberts, of Daleside Veterinary Group, one of the vets involved in the study.
But what was evident was how that damage had impacted on growth rates.
Analysis of the data revealed that average daily liveweight gain (DLWG) in the calves with abnormal scores was 0.17kg/day less than those that had no lesions.
Bedwyr says there weren’t enough calves with abnormal scores in that study that had also been treated to enable any difference in their growth rates to be compared to the calves without lesions.
But records showed that on four of the farms, no calves that had lesions had been treated for clinical BRD yet their growth rates were lower than those with clear scans, he adds.
“This suggests that clinical cases of BRD are just the tip of the iceberg, and its impact on calf growth and performance may affect many more calves than those showing clinical signs,’’ he says.
“This emphasises and raises awareness of the importance of monitoring calf health and performance, along with good calf management to minimise BRD.’’
What the study also showed was that half of the calves that had abnormal lung scores at the first scanning had normal scores at the second.
If there are surplus heifers on a farm, Bedwyr says TUS could form part of the decision tree on which of those to retain as replacements to ensure that only the most productive animals form the future herd.
Farming Connect Specialist Manager Menna Williams, who oversaw the project, says by assessing the level of lung consolidation, awareness had been raised on the farms of the level of subclinical respiratory disease in dairy calves, and its potential impact on herd efficiency and profitability.
There are also benefits to the dairy industry in general, she adds.
“This information will help motivate improvements in calf management on dairy farms in Wales with the aim of reducing respiratory disease and reduce the need for antimicrobial use in calves.’’
Another 100 calves across the study farms will be scanned in 2025.
Study farms
February - September 2024 timeline
Herd size from 80 - 650 cows
Block calving system on three farms
All-year-round calving pattern on five farms
All farm staff involved in calf rearing given training on detecting BRD clinical signs
Managing calves to prevent respiratory disease
Cases of respiratory disease can be prevented with good calf management protocols.
Bedwyr says everything from housing and bedding to colostrum intakes and stocking density must be considered.
He recommends housing calves in purpose-built facilities and getting the right balance between fresh air coming into the building but with no draughts at calf height.
He advises following Red Tractor guidelines on stocking density to avoid over-crowding.
Colostrum quality and intake quantities play a vital role in providing calves with the antibodies they need for disease prevention.
Farmers can use a refractometer to assess quality and, to establish if passive transfer of immunity has been achieved, to ask their vet to blood test a representative number of calves.
Bedding should be clean and dry, “to not squelch underfoot when it is walked on’’, says Bedwyr.
While not every farm will have the facilities to isolate calves displaying clinical signs, he highly recommends that if that possibility exists that they are.
CASE STUDY
The combination of spring calving and a well-ventilated rearing shed means cases of pneumonia in calves are very rare at Moor Farm, near Holywell, but with a high replacement rate the Davies family need to be confident that every heifer that enters their herd is capable of delivering her milk yield potential.
Lung scanning revealed just one calf with an abnormal score in the 2024-born heifers from the Holstein Friesian pedigree herd.
The score was not high and the calf had not displayed any clinical symptoms of respiratory infection.
Maintaining a tight calving block of eight weeks puts the herd replacement rate at 33% so attention to detail is a priority during calf rearing.
Newborn calves spend their first couple of days in small, straw-bedded pens of two before moving into a group of 10, reared on whole milk until weaning at eight weeks.
The rearing shed is airy with an open ridge, very different from the traditional barns where calves had previously been housed, says Rhys Davies, who farms with his parents, Dei and Heulwen.
“We had more cases of pneumonia when we were rearing in those barns,’’ he recalls.
Heifers are weighed regularly to keep them on target for mating at 15 months at between 350-380kg, depending on genetics.
Calving previously got underway in mid-February but that has now shifted to 20 March.
The land at Moor Farm is quite heavy and a succession of wet Februarys was one of the reasons the Davies’ pushed calving back as well as their milk buyer’s seasonality price penalties.
Because the farm has a good track record of calves not contracting respiratory infections, Rhys says he wouldn’t routinely use lung scanning but sees a good case for it in other systems where there is more pressure on calves at times of the year when the weather conditions are conducive to pneumonia.
“If I was autumn calving and the housing wasn’t great, I think it would be well worth that investment to check the extent of any lung damage before heifers joined the herd,’’ he says.
Rhys also wonders if there might be potential to use it to work out if there is a correlation between the genetic link to calf survivability and an abnormal TUS.
“It might help us to more accurately pinpoint the heifers to breed from,’’ he suggests.
FARM FACTS
- Ffrwd pedigree herd
- 113 Holstein Friesians plus followers
- Milk sold to Arla
- Milk yield average 7,500 litres at 4.59% fat and 3.65% protein
- 618kg milk solids a cow a year
