“Have you seen much pneumonia recently?” – a conversation opener offered by most farm clients around this time of year which indefinitely leads to their detailed account of the weather over the last few days. Although it may be the fifth time you’ve had the conversation that day, it is the perfect opportunity to review the client’s management of bovine respiratory disease (BRD) and spark discussion on the benefits of how early detection and treatment of BRD can reduce the impacts of disease.
BRD affects 46 percent of calves before they reach nine weeks of age (Johnson et al., 2017). A recent study by Dunn et al. (2018), using ultrasound images to assess the lung damage in young calves, revealed that lung lesions can develop as early as 12 days of age and can have long-term effects on the lifetime productivity of dairy heifers and beef calves (Table 1).
Many farmers will only consider the immediate treatment costs of BRD which could be conservatively estimated at £5 per case for medication alone, but this can just be the tip of the iceberg when compared to the long-term economic impact of decreased longevity and production. In reality, it is estimated that the overall cost of BRD would be closer to £772 per case in young dairy heifers (Table 2; Bartram et al., 2017).
The additional hidden costs are an accumulation of the impacts of delayed weaning (estimated at £3.53 per day; Boulton et al., 2015), delayed first calving, reduced longevity in the herd, reduced daily liveweight gain, reduced first and second lactation yields and replacement costs – the average price of freshly calved Holstein Friesian heifers at time of writing is £1,419 (AHDB, 2020). With these effects in mind, prevention, early detection and prompt treatment of BRD is essential to minimise its impact.
It is widely considered that the cause of BRD is multifactorial, and it therefore seems appropriate that the treatment of BRD should be too. Alongside the immediate treatment of cases with appropriate antibiotic and non-steroidal anti-inflammatory (NSAID) therapy, it is also important to verify that calves are receiving early immune protection from good colostrum management and nutrition.
BRD is heavily influenced by the environment and, although ventilation and humidity are critical, management changes play a monumental role in the success of treatment. Such changes can include providing jackets, increasing the volume or concentration of milk replacer in relation to seasonal declines in the average ambient temperatures and ensuring the hygiene of pens and feeding equipment. It is important that frequent group changes are avoided and that disbudding is done using a minimally invasive method at an appropriate age, and using local anaesthetic and NSAIDs in order to minimise undue stress which leads to susceptibility of disease.
Vaccination against BRD reduces morbidity, reduces severity of disease and also reduces nasal shedding of virus from infected calves. Concurrently these effects will help to reduce infection pressure (Masset et al., 2020). Uptake of vaccines among dairy and beef producers is disappointingly low, estimated at 25 percent of dairy calves and 35 percent of beef calves (Boulton et al., 2015). One suggested reason for this is that farmers’ understanding of the lifetime impact of respiratory disease is limited. It is possible in some circumstances to produce autogenous vaccines to help control emerging BRD challenges such as Mycoplasma spp.
Delaying antibiotic and NSAID therapy can lead to an increase in lung damage (lung consolidation) by the disease-causing organism. Lung consolidation describes the presence of heterogeneous hypoechoic areas in the lung tissue on thoracic ultrasound examination, usually as a result of infection, causing a decrease in the effective function of the lung tissue (Teixeira et al., 2017). The greater the lung consolidation, the lower the growth rate, the greater the risk of culling, the higher age at first calving and lower pregnancy to first service (Adams and Buczinski, 2016; Teixeira et al., 2017). It can be challenging for clients and practitioners to detect early signs of acute pneumonia. Several aids have been developed to assist farmers and practitioners in early detection of BRD.
- Scoring charts
UC Davis has developed a BRD scoring system for pre-weaned dairy calves. The scoring card illustrates varying severities of BRD clinical signs that are associated with a numeric score. The user adds up the scores of the clinical signs shown by their patient and if the score is greater than 5 the calf may be positive for BRD
Thoracic ultrasound has been proposed as a calf-side tool to aid BRD diagnosis. Thoracic scanning can be used to confirm farm employee’s detection of respiratory disease, assess animals with unknown respiratory disease history and help a farmer to make management decisions. Thoracic ultrasonography of the lungs is performed using a 6.2MHz linear transducer screening the right 2nd through 10th and left 3rd through 9th intercostal spaces. Each calf is classified as not having lung consolidation (hyperechoic line with reverberation artifact with or without comet tail) or with lung consolidation (any detectable heterogeneous hypoechoic area) using a scoring system detailed by Cramer and Ollivett (2019). More useful information and descriptive videos on this technique are available online (University of Wisconsin-Madison, 2021)
- Smart ear tags and technology
Temperature-sensing ear tags are designed to detect increases in a calf’s body temperature before it displays clinical signs of disease. Similarly, activity collars are able to detect changes in a calf’s activity and feeding behaviour if paired with a milk feeding system, which can help aid early detection of BRD. The limitation to these technologies is that they can encourage overuse of antibiotics, be costly in commercial settings and be difficult to set up/use (Mahendran, 2020)
Necropsy may seem an oxymoron for early detection of BRD but can prove an invaluable examination that lends itself to aid prompt diagnosis in an acute outbreak of severe pneumonia where fatalities are seen. CPD training courses are worth enquiring about through local veterinary laboratories, veterinary schools or pharmaceutical company representatives
The most common BRD pathogens are viruses. Therefore, antibiotics are used to help prevent or treat secondary infections rather than the primary cause. In group outbreaks where a viral pathogen is suspected, it is important to consider the use of live intranasal vaccines as treatment. Alongside an antibiotic and/or vaccine it is imperative to consider the use of NSAIDs. The use of NSAIDs has welfare and economic benefits since it has been proven to reduce pyrexia and lung consolidation, therefore minimising reduction in daily liveweight gain (Friton et al., 2005). In turn, maintaining daily liveweight is critical to reducing the risk of long-term production and economic losses such as delayed calving and reduced milk yield. There are several NSAIDs available for use in cattle. Meloxicam has the benefit of having a longer duration of activity than some other products. Furthermore, combination products containing antibiotic and NSAID in one injection make treatment easier and protocols simpler for clients, ensuring that every calf receives the NSAID it requires.