Vets are urging farmers to put in place mitigation strategies to curtail a surprising increase in respiratory disease linked to immunosuppression in young, suckled, grazing calves.
The rise in cases of classic pneumonia in suckled calves at grass in May, June and July has been significant, says Colin Mason, veterinary investigation officer at Scotland Rural College’s (SRUC) Disease Surveillance Centre, Dumfries.
See also: Advice on reducing pneumonia risk as autumn weather swings
“The thing that’s surprising is it’s occurring at a time when animals should be living their best life: they’re outside, suckling their dam’s milk, on good grass – especially in Scotland. They’re not wanting for anything.”
Unlike parasitic pneumonia associated with lungworm, which is often seen at grass in August and September, these cases are typically bacterial infections.
Colin explains that bacterial pneumonia is an “opportunist” that will take advantage of a compromised animal.
This is seen in the case data, with many individuals showing sign of predisposing factors that are potentially compromising immunity and acting as a gateway for respiratory issues.
The four main predisposing factors are:
1 Tick-borne disease
Colin estimates that 20% of cases of respiratory disease in first-grazing suckler calves could be tick related.
Tick-borne fever, for example, will compromise the immunity of infected cattle by negatively affecting white blood cells.
Tick-spread and tick-borne diseases are on the rise, making it an area for concern for all farmers, regardless of geography (see “Tick-borne disease on the up”).
Prevention involves avoiding ground with dense vegetation or long grass.
Licensed pour-on treatments can also be used, but options are limited and climate change and increased tick spread may mean a different approach is required in the future.
“We might have to think about how we breed cattle that are more resistant to ticks. We can’t be wholly reliant on chemicals to control the problem, we need to find sustainable solutions to cope,” he says.
2 Vitamin and trace element status
Vitamin E and selenium are important for immunity, particularly in fast-growing continental calves.
“Their requirements for vitamin E and selenium can be quite high to manage oxidative stress in growing muscles.
“It’s down to whether they’re getting sufficient,” Colin says.
More than half of all calves presented for post-mortem at SRUC Veterinary Services between 2016 and 2020 had signs of deficiency (see table), which could be compromising their immune status.
Colin urges farmers to ensure suckler cows are supplemented sufficiently, including during outwintering and after turnout, when it can be forgotten. That way, trace elements can be transmitted to calves via the dam’s milk.
Calves should be supplemented accordingly.
When calf pneumonia is a problem at grass, he suggests working with a vet to blood test six typical cows to establish selenium and vitamin E status.
Appropriate supplementation can then be planned and could involve boluses, supplementing dams or providing licks.
Level of mineral and trace element deficiency in calves at post-mortem
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Post-mortems reveal high incidence of vitamin E and selenium deficiency |
Trace element
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Percentage of results deficient
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Vitamin E
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58%
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Selenium
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54%
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Cobalt
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17%
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Copper
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6%
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Source: Review of beef calf mortality from SRUC Veterinary Services, based on 1,662 post-mortems carried out 2016-2020 of calves less than six months old , 24% of whom had respiratory disease
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3 Bovine viral diarrhoea
Exposure to bovine viral diarrhoea (BVD) will have a negative impact on any animal’s ability to mount an effective immune response. The key is to work with a vet to understand a herd’s BVD status and design a herd-specific control strategy.
This should focus on routine testing, vaccination, and identifying and removing persistently infected animals, which act as the main route of infection.
4 Coccidiosis
Coccidiosis can cause acute, bloody scours or death, but more commonly can simply reduce calf resilience and act as a gateway disease for other problems.
“Very often, respiratory disease follows on from an episode of gut disease, so it’s always worth reviewing coccidiosis status as part of this,” Colin suggests.
This should involve working with a vet to identify risk factors, putting preventive strategies in place with a focus on exceptional hygiene, and targeting treatment as necessary.
In general, any unexplained calf deaths at about eight weeks old should also be investigated, to ensure any issues are addressed promptly.
“You’re not expecting calves to die at that stage, especially of respiratory disease, so [even] small levels [of mortality] are significant,” Colin emphasises.
Case study: BVD exposure linked to respiratory disease
Immunosuppression caused by bovine viral diarrhoea (BVD) exposure was the root cause of “quite extreme” respiratory disease on a Scottish farm where beef calves graze the lower hill.
The farm’s vet, Rachel Bragg, of the Farm Animal Practice at The Royal Dick Veterinary School, says 30 calves aged between five days and one month old required treatment for pneumonia in the 250-cow suckler herd.
Treatments increased soon after a routine BVD test found a persistently infected (PI) calf, which was then removed.
“The PI was found quite early on, but the respiratory effects lasted for some months afterwards,” she says.
A couple of calves were lost, while others were repeat treated.
“The earlier they were caught, the better the response.”
The incidence was surprising considering weather and grazing conditions were good, says Rachel.
She urges farmers to question any unusual respiratory disease patterns, as they could be an indication of something else causing immunosuppression.
In addition, those calves that recover after treatment for pneumonia will be more likely to grow suboptimally and succumb to pneumonia again at housing because of long-term lung damage.
With that in mind, having a vaccination programme in place prior to housing is essential, she says.
Tick-borne disease on the up
Tick-borne disease now needs to be considered on most farms, given ticks’ widening geographical spread.
According to data from Scotland’s Rural College Veterinary Services centres, diagnosis of redwater fever and tick-borne fever have doubled since 2010, while the spread of these diseases has increased in Scotland.
Historically, ticks were more of a problem in the west of Scotland and England and in upland rough grazing.
However, Colin Mason says they are now also seen further east and on lowland pastures. In addition, increased tree planting in Scotland has created the perfect thick vegetation for ticks.
This means more farmers need to develop preventative strategies.
In Dorset, vet Lucy Hepworth of Friars Moor Livestock Health, has not seen more pneumonia in beef calves at their first grazing.
However, she has noticed an increase in tick risk and tick-borne disease over the past 20 years.
As a result, she says it is something that increasingly needs to be considered.
“The farm/vet team should look at whether it’s in the background when assessing disease in youngstock,” Lucy says.
Although youngstock need to be exposed to ticks to some degree to build a level of immunity, issues arise when tick levels are high.
“We don’t want them to be exposed massively, as it overwhelms their immune response. That’s where it suppresses immunity and allows other diseases to take hold,” she says.