Benefits of scanning the lungs in dairy calves
Garon O., Bohemen B. et al Club Bovin, Faculté de médecine vétérinaire, Université de Montréal, CP5000, Saint-Hyacinthe, J2S 7C6, Québec, Canada
In Canada and in the United States of America, quite often dairy calves do not receive all the attention they deserve. In part this can be explained because they do not contribute to the immediate income on the farm. For example, when it comes to the lactating animals of a herd, a lot of effort is deployed in order to avoid milk loss caused by metabolic diseases and mastitis, since the financial losses associated to these conditions are felt and seen immediately. However, because there is a waiting period of about two years before the first drop of milk is produced and sold, dairy calves are viewed as a major expense. Hence why they do not receive the attention they deserve. It is recognised that young dairy animals are more vulnerable to health issues in comparison with older individuals. It is of primordial importance to identify these diseases as early on as possible in order to address them and to prevent them in order to minimise their potential impact on the future productive life of the animal.
With regards to health in young dairy calves two main concerns must be considered of importance; diarrhea and respiratory disease. The aim of this clinical article is to underline the benefits of scanning the lungs in dairy calves and to encourage bovine veterinary practitioners to use the ultrasound technology available for this use given its simplicity.
Bovine respiratory disease (BRD) is one of the principal health issues that affects dairy calves. The consequences of this disease are numerous and may most likely result in a major impact on the future life of these calves within the herd. Relapse of the condition, mortality, decreased growth rate and dissemination of the infectious agents, only to name a few, are all potential consequences of BRD when it affects young dairy replacement subjects. Moreover, adding to these consequences we must also include the cost of antibiotic treatments and the additional labor costs. Studies have demonstrated that dairy calves treated for respiratory diseases prior to three months of age were times more likely to die after three months of age in comparison to a control group of healthy calves of the same age. That being said, we can affirm it is important to find a way to detect BRD as early as possible, including the subclinical forms of the disease. There are economic impacts of importance related to the subclinical form even though it can be easily missed during a routine examination of the animal.
Clinical signs such as hyperthermia, anorexia, lethargy, abnormal respiratory noises, tachypnea and dyspnea are all important in order to recognise clinical cases of BRD. Clinical signs of individual calves can be scored using various scoring system to diagnose BRD.These scoring systems can help producers identify sick calves and establish a treatment based on veterinary protocols. However, identifying the subclinical form of BRD or chronic pulmonary lesions is much more difficult. Nonetheless, more difficult does not rhyme with impossible! Thoracic ultrasonography (TUS) is an excellent tool to recognize subclinical or chronic lesions.
Firstly, it has been demonstrated that thoracic ultrasonographic images are highly correlated with radiographic images and necropsy lesions noted in dairy calves. Studies evaluating the thoracic ultrasonography as a test for diagnosing BRD, in which there was a confirmation of the BRD status through necropsy, reported a sensibility from 86 to 94% and a specificity from 98 to 100%. Another study reports that upon diagnosing bronchopneumonia (BP) in dairy calves, the sensibility and specificity using only pulmonary auscultation was only 72.9% and 53.3%, respectively. When adding thoracic ultrasonography to the auscultation, the precision to detect BP increased significantly. Therefore, ultrasonography is an excellent noninvasive method to identify antemortem pulmonary lesions with dairy calves.
Secondly, thoracic ultrasonography has other advantages, which makes this technique interesting for the diagnosis of subclinical BRD. Ultrasound is already widely used for early pregnancy diagnosis, therefore a large number of dairy practitioners already possess a portable ultrasound with an 8.5 MHz linear probe. This same equipment can be used to perform a thoracic ultrasonography, which avoids the purchase of additional equipment. During thoracic ultrasonography, it is not necessary to shave the thorax. Furthermore, every practitioners has easy access to 70% isopropyl alcohol which can be used as a media for ultrasound transmission to obtain good quality images. In order for the scan to be complete, it is important to know the anatomy of the bovine lungs and their external landmarks that can be identified on the calf. The scan must be systematic, each intercostal space must be scanned from top to bottom on all its length and each side must be scanned thoroughly. The left lung extends from the 2nd to the 10th intercostal space, whereas the right lung extends from the 1st to the 10th intercostal space. Pulmonary lesions may be noted in accordance to diverse scoring systems (some being more complete than others). The use of the ultrasound for a pulmonary examination is quick, varying between 30 seconds to 5 minutes per calf depending on the experience of the ultrasonographer with the technique and the scoring system used.
In addition to being a rapid technique, it is also a very simple one, with low associated costs which has been well described in the literature. Recently, a study evaluated the results obtained from thoracic ultrasonography and the user’s experience. The conclusion retained was that the pulmonary consolidation lesions evaluated with the ultrasound had good to excellent intraclass correlation coefficients and results were comparable between users regardless of their experience.
In summary, the thoracic ultrasonography has its place in our actual farms to help with live dairy calf diagnosis of pulmonary conditions and can be consistently performed with adequate training even with novice ultrasound operators.
The benefits of recognising individuals with lesions
Respiratory diseases are a major issue for dairy calves, mainly because the signs in calves are not always obvious. As mentioned earlier, with dairy calves, respiratory diseases are associated to higher production costs, a higher risk of mortality and relapse, as well as a reduction in growth rate and an early cull. A recent study has demonstrated that subclinical BRD diagnosed based on the detection of pulmonary consolidation by systematic thoracic ultrasonography in dairy calves was associated to a significant reduction of their growth rate as heifers later on. It has also been demonstrated that calves with severe pulmonary lesions had significantly less chance to survive through their first lactation. Recently, another study concluded that the presence of at least one pulmonary consolidation area (≥3cm), within the first 8 weeks of life of replacement heifers resulted in a loss of 525 kg (1155 lbs) of milk at 305 days in milk during their first lactation.
Furthermore, heifers without pulmonary consolidation have a tendency to a higher conception rate (62.0%) following artificial insemination in comparison with heifers that had pulmonary consolidations (52.5%). The ultrasound is an objective tool (whether the lesion is present or not) for diagnosing BRD which can be simply applied/integrated to a screening examination on the farm, at a fixed time period, in order to target specific individuals or groups at risk of underperforming or being culled earlier. A producer who has access to a professional who can use this tool will be capable of identifying potentially non-productive animals with accuracy within their first months of life. This would allow a choice between two options. The first would be removing the animal early on, which would benefit in fewer wasted days on feed, a reduction of money spent on treating future pneumonia treatments, overall herd profitability and animal welfare can both be improved. Alternatively, an animal with a good genetic background could be kept with the understanding that this animal may never live up to their full genomic potential. The producer could also apply specific treatment protocols or tools in order to help the young affected calf heal.
In summary, one must keep in mind that with an adequate technique and a portable ultrasound, one that the bovine practitioners can already use for reproductive examinations, it is possible to quickly scan and evaluate the condition of the lungs in dairy calves. The procedure is quite precise and accurate, it is also possible to withdraw pertinent information about pulmonary lesions associated to BRD in dairy calves. On an individual basis, thoracic ultrasonography helps to identify negative prognostic risk factors, which can help producers to take the decision of an earlier cull. On a herd level, the ultrasound can help identify groups of animals that are at risk of developing respiratory problems (BRD being the main concern), to monitor the prevalence and the severity of lesions throughout time. Furthermore, management changes such as vaccination, ventilation and any labor change can all be evaluated. Thoracic ultrasonography can be viewed as an added value to the service offered by veterinarians and gives an excellent opportunity to improve animal health. A service of this kind can also offer an added opportunity for the veterinarian to develop a bond of trust with his producers. On the long run this may allow an easier approach when there is a desire to address other problems found on the farm or aspects that could help improve the producers profitability and/or the welfare of the herd.