The intensive use of antimicrobials in the veal industry is heavily criticized, but drivers for antimicrobial usage (AMU) are still poorly understood. The industry fears that a drastic reduction in AMU would increase mortality, creating an unacceptable welfare issue. The objectives of the present study were to identify risk factors for AMU and to explore the relationship between AMU and mortality. A retrospective cohort study was performed on the antimicrobial registration data from the largest Belgian veterinary veal practice. The data set contained 295 production cycles from 78 farms, representing 146,014 calves and 8 veal companies (also called integrations). The average AMU was 32.3 defined daily dose animal per year (standard deviation: 11.04), of which 76.2% was administered orally and 23.8% parentally. The AMU remained stable between 2014 and 2016 with only a slight, but significant increase in total AMU between 2015 (31.0 defined daily dose animal per year, standard deviation: 10.5) and 2016 (35.1, 10.8). Use of almost all antimicrobial classes decreased over 2014 to 2016; however, use of long-acting macrolides, doxycycline, and aminosides increased significantly. Analysis identified breed (higher use in beef calves compared with dairy and crossbreeds), month of arrival (lower use when arrived in April or May compared with winter months), and veal company as risk factors. The veal company not only significantly affected total AMU, but also affected the majority of the antimicrobial classes. Additionally, breed differences were present for oxytetracycline, colistin, and classic macrolides, and a month effect was present for doxycycline only. These data illustrate that this veterinary practice realized a reduction of 46% in total AMU and of 96% in critically important antibiotics (fluoroquinolones, cephalosporins of the third and fourth generation) compared with the Belgian benchmark from 2007 to 2009. Replacement of critically important drugs by an increased use of long-acting macrolides is worrisome. Mortality risk was very low compared with benchmarks referenced internationally and did not increase with decreasing AMU. Use of trimethoprim-sulfonamides was a risk factor, whereas use of oxytetracycline was a protective factor for mortality. The absence of a relationship with mortality at the current levels of AMU suggests that a further rational reduction is possible. Attention should be paid to consider different AMU benchmarks for different breeds and to include the veal company as a target for antibiotic awareness campaigns.

Mycoplasma bovis is a leading cause of pneumonia but also causes other clinical signs in cattle. Since no effective vaccine is available, current M. bovis outbreak treatment relies primarily on the use of antimicrobials.

Bovine respiratory disease (BRD) continues to be a leading cause of economic loss, hampered animal welfare, and intensive antimicrobial use in cattle operations worldwide. Reduction of antimicrobial use is hindered because it is still unclear which clinical signs are best monitored to reliably detect pneumonia. Also, these clinical signs may vary according to age and between breeds. The objective of this cross-sectional study was to identify clinical signs associated with ultrasound-confirmed pneumonia (lung consolidation ≥1 cm depth) pre- and postweaning in different production types (dairy, beef, and veal) and breeds. A total of 956 calves (70% Holstein-Friesian dairy and 30% Belgian Blue beef) from 84 herds were clinically examined using 24 parameters, scored using the Wisconsin and California BRD clinical scoring systems and subjected to thoracic ultrasonography. Of the calves, 42.8% and 19.5% had a lung consolidation ≥1 cm and ≥3 cm, respectively. Cough, both spontaneous and induced, was the only and best-performing clinical sign statistically associated with lung consolidation in all production types. Fever (rectal temperature ≥39.4°C) was the second most promising factor, being significant in beef and veal calves but not in dairy calves. Postweaning, none of the clinical signs studied were statistically associated with pneumonia, with the exception of cough in dairy calves. Spontaneous or induced cough as a single clinical sign outperformed any combination of clinical signs, including the Wisconsin and California respiratory disease scoring systems, but sensitivity remained low. This information can be useful to select appropriate clinical signs for continuous monitoring in precision livestock applications, targeted to a given breed and age. As a cross-sectional measurement, diagnostic accuracy of spontaneous cough (accuracy = 65.1%, sensitivity = 37.4%, specificity = 85.7%) is too low to be used as a criterion to select animals with pneumonia for antimicrobial treatment. At the group level, cough monitoring holds potential as an early warning sign, after which lung ultrasonography should follow.

Rapid identification of Mycoplasma bovis infections in cattle is a key factor to guide antimicrobial therapy and biosecurity measures. Recently, Nanopore sequencing became an affordable diagnostic tool for both clinically relevant viruses and bacteria, but the diagnostic accuracy for M. bovis identification is undocumented.

Quick thoracic ultrasonography (qTUS) is increasingly used as an on-farm method to diagnose clinical and subclinical pneumonia in dairy calves. The primary objective of this prospective cohort study was to describe dynamics of lung consolidation in a purchase-dependent production system for male dairy calves in relation to antimicrobial therapy and respiratory diagnostics. In addition, we studied the association of cured and uncured pneumonia with average daily gain (ADG) and cold carcass weight (CCW). The third objective was to determine the effects of arriving with lung consolidation on the probability of developing chronic unresponsive pneumonia and reduced performance. A total of 295 male dairy calves were intensively followed by qTUS and clinical scoring on 7 strategic occasions (wk 1, 2, 3, 4, 6, 8, and 12) during the production cycle. Of the calves, 17.6% (52/295) arrived with a lung consolidation ≥1 cm. At the first outbreak of respiratory disease (wk 1 after arrival), this incidence had risen to 30.8%. Initial therapy with tulathromycin and subsequently doxycycline appeared ineffective, resulting in a increase to 43.8% of calves having pneumonia in wk 4. At the start of the first outbreak (wk 1), the majority (86.8%) of the pneumonia cases were subclinical. At wk 4, the outbreak became more clinical, and treatment with amoxicillin resulted in a cure risk of 52.7%. Culture and nanopore sequencing diagnostics on nonendoscopic broncho-alveolar lavage (nBAL) samples identified bovine respiratory syncytial virus and Mycoplasma bovis as the dominant agents in the first outbreak. The isolated M. bovis strain showed mutations associated with macrolide resistance. The second outbreak was characterized by a Pasteurella multocida superinfection and isolation of multiple M. bovis strains from nBAL diagnostic testing. Evaluated over the complete observation period, 83.4% of the calves developed consolidations ≥1 cm on qTUS. Of these calves, 53.9% (135/246) were cured by antimicrobial therapy. Chronic pneumonia (≥30 subsequent days of pneumonia) was seen in 13.9% of the animals (n = 41). Calves with uncured or chronic pneumonia had a lower ADG (992 ± 174 g/d and 930 ± 146 g/d, respectively) compared with calves that never developed pneumonia (ADG = 1,103 ± 156 g/d). In contrast, calves that did fully cure trended toward a lower ADG than calves that never developed pneumonia, but differences were no longer significant. Also, the effect of uncured pneumonia was no longer significant for CCW. Calves with lung consolidation upon arrival had a lower ADG (981 ± 159 g/d vs. 1,045 ± 159 g/d) and were more likely to develop chronic pneumonia [odds ratio = 4.2; 95% confidence interval = 2.1-8.6] compared with calves without consolidation upon arrival. Animals with chronic pneumonia, in turn, had a lower CCW than animals without chronic pneumonia (10.3 ± 4.4 kg; 95% confidence interval: 1.6-19.1 kg). This study documents the consequences of subclinical pneumonia upon arrival and pneumonia developed later in the production cycle on production outcomes in a veal calf setting. Both qTUS and nBAL diagnostics provide important information, offering potential for better control and prevention of bovine respiratory disease in dairy calves.

Mycoplasma bovis is a leading cause of pneumonia in modern calf rearing. Fast identification is essential to ensure appropriate antimicrobial therapy. Therefore, the objective of this study was to develop a protocol to identify M. bovis from bronchoalveolar lavage fluid (BALf) with MALDI-TOF MS and to determine diagnostic accuracy in comparison with other techniques. BALf was obtained from 104 cattle and presence of M. bovis was determined in three ways: (1) BALf was enriched and after 24, 48 and 72 hours of incubation analyzed by MALDI-TOF MS (RIMM), (2) triplex real-time PCR for M. bovis, M. bovirhinis and M. dispar and (3) ten day incubation on a selective-indicative agar. Diagnostic accuracy of the three tests was determined with Bayesian latent class modelling (BLCM). After 24h of enrichment, M. bovis was identified by MALDI-TOF MS in 3 out of 104 BALf samples. After, 48 and 72h of enrichment, 32/104 and 38/100 samples were M. bovis positive, respectively. Lipase positive Mycoplasma-like colonies were seen in 28 of 104 samples. Real-time PCR resulted in 28/104 positive and 12/104 doubtful results for M. bovis. The BLCM showed a sensitivity (Se) and specificity (Sp) of 86.6% (Confidence Interval: 69.4%-97.6%) and 86.4% (CI: 76.1-93.8) for RIMM. For real-time PCR Se was 94.8% (89.9-97.9) and Sp 88.9% (78.0-97.4). For selective-indicative agar, Se and Sp were 70.5% (52.1-87.1) and 93.9% (85.9-98.4), respectively. These results implicate that rapid identification of M. bovis with MALDI-TOF MS after an enrichment procedure is a promising test for routine diagnostics in veterinary laboratories.