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Morbidity, mortality and drug use in white veal calves with emphasis on respiratory disease

Bart Pardon UGent (2012)
abstract
The veal industry is specialized in rearing male calves on a low iron milk diet, hereby obtaining white meat. As in other food animals, high levels of antimicrobial resistance have recently been detected in bacteria from veal calves, potentially threatening treatment options in both human as veterinary medicine. This worrisome observation is currently overwhelming veterinary medicine and revisions of current treatment practices (benchmarking) and the prudent use of antimicrobials in food animals are highly recommended by the European authorities. As a general introduction (Chapter 1.1.), an overview of the typical characteristics and challenges of the Belgian white veal industry is given. A synthesis of the current knowledge on antimicrobial resistance in pathogenic, zoonotic and commensal bacteria from veal calves is provided. Bovine respiratory disease (BRD) is the leading cause of morbidity and mortality in young animals in almost every cattle production system worldwide. BRD is a multifactorial disease resulting from the complex interaction of pathogens with host factors (immunity) and the environment, and is therefore also termed bovine respiratory disease complex (BRDC). The BRDC differs in between production systems, and knowledge on the epidemiology and pathogenesis of BRD in each production system is necessary, in order to determine effective control measures for that particular production system. In chapter 1.2. an overview of the constitution of the BRDC in veal calves is given. From this literature review it could be concluded that, under the current organization of the industry, veal calves are at ultra-high risk of developing BRD, making antimicrobial use necessary to overcome disease. Hardly any information on the pathogens involved in the BRDC of veal calves is available. For economic reasons and due to a lack of epidemiological knowledge on diseases in veal calves, veterinarians have been tied to empiric, often blind, treatment in the veal industry for decades. In line with this problematic situation and with the emergence of antimicrobial resistance, the overall objective of this doctoral thesis was to gain insights into current practices, into the epidemiology of morbidity and mortality in the Belgian white veal industry and into the underlying pathogens of respiratory disease (Chapter 2). This to provide the industry with objective data from where to install and evaluate sustainable preventive and therapeutic protocols, using less antimicrobials, in the future. At present, no information on drug use in white veal calves in Belgium is available. Therefore, the first objective was to document antimicrobial and anti-inflammatory drug use in the Belgian veal industry (Chapter 3). A prospective study was installed, monitoring group and individual drug use on 15 veal cohorts in Belgium. Treatment incidences (TI) based on animal defined daily dose (ADD), prescribed daily dose (PDD) and used daily dose (UDD) were calculated. Antimicrobial drug use was highly intensive, with on average 416.8 ADD per 1000 animals at risk. Antimicrobial drug use consisted for 95.8% of oral group treatments, and only for 4.2% of individual administrations. BRD was the main indication for both group (53.0%) and individual drug use. The most frequently used antimicrobials (group treatments) were oxytetracycline (23.7%), amoxicillin (18.5%), tylosin (17.2%) and colistin (15.2%). Deviations from the leaflet recommendations were frequently encountered, with 47.3% of the group treatments underdosed (predominantly oxytetracycline and tylosin to treat dysbacteriosis). Based on the UDD, smaller integrations (less than 50 herds) used more antimicrobials than larger ones. Producers used higher dosages in group treatments than prescribed by the veterinarian in cohorts with a single caretaker. A large variety of antimicrobial compounds were used for individual treatments, including the critically important cephalosporins (8.0%) and fluoroquinolones (12.6%). Individual treatments were generally overdosed. Anti-inflammatory drugs were far less frequently used (TIUDD= 5.94), mostly sodium salicylic acid in group treatments. Individually administered anti-inflammatory drugs were generally overdosed. The main conclusion was that antimicrobial drug use is highly intensive at present and that future reduction can only be achieved by reducing the number of oral group treatments. In a second study (Chapter 4.1.), the objective was to determine the causes and epidemiology of morbidity and mortality in dairy, beef and crossbred white veal production in Belgium. A total of 5853 calves, housed in 15 production cohorts (5 per breed), were followed during one production cycle. Causes of mortality were determined by necropsy. Morbidity was daily recorded by the producers. The total mortality risk was 5,3% and was significantly higher in beef veal production compared to dairy or crossbreds. The main causes of mortality were pneumonia (1.3% of the calves at risk), ruminal disorders (0.7%), idiopathic peritonitis (0.5%), enterotoxaemia (0.5%) and enteritis (0.4%). Idiopathic peritonitis was identified as a disease of unknown origin, specifically occurring around 8-10 weeks after arrival. Belgian Blue beef calves were more likely to die from pneumonia, enterotoxaemia and arthritis. Detection of bovine viral diarrhea virus (BVDV) at necropsy was associated with chronic pneumonia and pleuritis. Of the calves, 25.4% was treated individually and the morbidity rate was 1.7 cases per 1000 calf days at risk. The incidence rate of respiratory disease, diarrhea, arthritis and otitis was 0.95, 0.30, 0.11 and 0.07 cases per 1000 calf days at risk, respectively. Morbidity peaked in the first three weeks after arrival and gradually declined towards the end of the production cycle. BRD already occurred immediately after arrival, but peaked 3 weeks after arrival. A long tail in the treatment curve was observed, associated with chronic pneumonia (relapse rate= 10.2% on average). It could be concluded that, whereas the group of digestive diseases was responsible for most mortalities, BRD was the single leading cause. BRD was also the main cause of morbidity, and a long tail of chronic disease, associated with BVDV at necropsy, was observed. Next, the impact of BRD, diarrhea, otitis and arthritis on mortality and carcass traits was studied in a sample of 3519 white veal calves (10 cohorts) (Chapter 4.2.). Disease registration was based on individual treatment by the producer and cause of death was determined by necropsy. Carcass data (hot carcass weight (HCW), color and fatness degree) were obtained from the slaughter houses. Average daily gain (ADG), carcass value (CV) and CV reduced by treatment costs were calculated. In comparison to non-treated calves, calves treated once for BRD showed a 0.066 kg/day reduction in ADG and 8.2 kg reduction of HCW, had a lower carcass value, a lower fatness degree and an increased mortality risk. The reduction in ADG, HCW, CV, fatness degree and the mortality risk increased dramatically with increasing number of BRD treatments. Calves treated multiple times for BRD also had higher odds for low carcass quality and were more likely to be classified as too red meat for white veal production. Arthritis increased the mortality risk, but reduced HCW only when associated with BRD. Otitis did not affect any of the studied parameters. Diarrhea increased the mortality risk, reduced ADG and HCW by 0.078 kg/day and 8.8 kg, respectively, and decreased carcass quality. It could be concluded that even under intensive coverage by oral antimicrobial group treatments, substantial economic losses occur in calves, which require individual treatment for BRD, diarrhea or arthritis. Controlling calf health by effective preventive and therapeutic strategies and in particular the prevention of chronic BRD is key for the profitability of veal operations. Because of the importance of BRD in morbidity, mortality and the associated drug use, further focus was on the identification of the pathogens involved in the BRDC of white veal calves in Belgium. In a fourth study (Chapter 5.1.), the prevalence of respiratory pathogens in diseased, unvaccinated, routinely medicated veal calves was determined, by sampling 24 natural outbreaks of BRD in Belgium (15 herds). Bacteria were cultured from nasopharyngeal swabs and seroconversion against viruses and Mycoplasma bovis was determined on paired sera. The inclusion criterion for sampling, was 10% of the animals with respiratory symptoms. Most outbreaks (75%) occurred between week 2 and 4 after arrival. In 54.2% of the outbreaks (13/24), antimicrobial group treatments for BRD had already been installed before the sampling criterion was reached, and in 29.2% (7/24) calves were still receiving oral antimicrobials at sampling. At the individual calf level, Mycoplasma spp., Mannheimia haemolytica and Pasteurella multocida were retrieved from 70.5%, 21.5% and 26.0% of the swabs, respectively. At the herd level the presence of M. bovis could be confirmed on 84.6% of the examined herds. Serological evidence of BVDV, parainfluenzavirus type 3 (PI-3), bovine respiratory syncytial virus (BRSV), bovine adenovirus 3 (BAV-3), bovine coronavirus (BCV) and bovine herpesvirus 1 (BHV-1) infection was present on 71.4%, 53.3%, 40.0%, 46.7%, 30.0% and 26.7% of the herds, respectively. At necropsy, Mycoplasma spp. could be cultured from 61.9% of pneumonic lungs (n=21) and respectively 60.0% and 20.0% of the tested calves were BVDV (n=20) and BRSV (n=16) PCR positive. It can be concluded that BRD in white veal calves is of slow progressive nature rather than massive acute outbreaks, likely due to the presence of maternal immunity and the frequently applied metaphylactic antimicrobial therapy. Under such conditions the peak incidence is reached on average at week 3 post arrival. At that time, next to a variable viral component in the individual calf, (multi)resistant Pasteurellaceae are prevalent. Overall, M. bovis and BVDV appear to play an important role in both the initiation of BRD (acute outbreak) as in lethal chronic cases. In a final study (Chapter 5.2.), the seroepidemiology of respiratory infections along the white veal production cycle and their association with BRD and carcass traits was determined. Also, the potential value of total and respiratory pathogen specific antibody levels at arrival to predict subsequent BRD and suboptimal carcass traits was evaluated. A total of 467 calves, housed in 15 veal herds, were sampled at arrival and 6, 12 and 24 weeks later. Antibody levels to 7 respiratory pathogens were determined at each time point by semi-quantitative ELISA. Circulation of PI-3, BAV-3 and M. bovis was detected in all studied herds. For BVDV, BRSV, BHV-1 and M. haemolytica 93.3% (13/15), 80.0% (12/15), 53.3% (8/15) and 86.7% (13/15) of the herds were infected, respectively. The respiratory disease peak in the first 6 weeks after arrival was associated with seroconversion to M. bovis (44.2% of the calves) and BVDV (32.0%). More than 50% of the calves seroconverted to at least one virus in this period, whereas seroconversion to M. haemolytica was not associated with the BRD peak. The prevalence of calves, persistently (PI) and transiently infected with BVDV, was 0.6% and 1.5%, respectively. PI calves had very low survival chances. With exception of M. bovis (10,7% of the calves on average), maternal antibodies were abundantly present at arrival for most pathogens, with little variation between herds. A worrisome 40.1% of the calves on average, ranging from 24.0 to 59.9%, had low total IgG levels at arrival, suggesting failure of passive transfer. Calves, seropositive to PI-3 and M. bovis at arrival, had a decreased and increased risk for BRD, respectively. Low (<8g/L) total IgG at arrival tended towards an increased BRD risk. No associations with carcass traits were found. Under the current medical management, the serostatus for respiratory pathogens at arrival was of little practical use to classify veal calves according to BRD risk or to predict carcass traits. To help improve the validity of epidemiological studies in the veal industry, standard case definitions should be provided and group antimicrobial treatments avoided. In the general discussion (Chapter 6), first, the value of the applied study methodology for veal calf health monitoring systems and future holistic studies is discussed. With the obtained insights into the epidemiology of veal calf diseases (predominantly BRD) in mind, the general discussion mainly aimed at critically reflecting on the current (medical) management practices. A series of possible short and long term measures to control BRD and reduce antimicrobial use, to be evaluate in the future, is proposed. Overall, it could be concluded that BRD is the main cause of morbidity and mortality in veal calves and subsequently the main indication for the highly intensive drug use in the Belgian veal industry. Despite the frequent antimicrobial coverage, the economic consequences of disease in calves requiring individual treatment were devastating. Almost every BRD pathogen was present on each herd, with a viral component in over 50% of the calves. Overall M. bovis and BVDV were most prevalent in acute and chronic BRD in white veal calves. The high prevalence of calves with insufficient levels of IgG at arrival is worrisome and requires attention at the herds of origin. Both the applied monitoring techniques as the obtained results can guide the veal industry in their search for evidence based preventive and therapeutic protocols, reducing antimicrobial use, while maintaining production results and animal welfare standards. More in specific, modifying current medical management towards M. bovis, exclusion of PI animals from veal production, vaccination and optimization of maternal immunity might be beneficial measures to reduce the BRD incidence and herewith associated antimicrobial use in veal calves.
Please use this url to cite or link to this publication:
author
promoter
UGent, UGent and UGent
organization
alternative title
Morbiditeit, mortaliteit en antibioticumgebruik bij witvleeskalveren met de nadruk op ademhalingsstoornissen
year
type
dissertation (monograph)
subject
keyword
antimicrobial use, drug use, mortality, morbidity, veal, BRD
pages
316 pages
publisher
Ghent University. Faculty of Veterinary Medicine
place of publication
Merelbeke, Belgium
defense location
Merelbeke : Faculteit Diergeneeskunde (kliniekauditorium B)
defense date
2012-10-01 17:00
ISBN
9789058643087
language
English
UGent publication?
yes
classification
D1
additional info
dissertation consists of copyrighted material
copyright statement
I have transferred the copyright for this publication to the publisher
id
3007344
handle
http://hdl.handle.net/1854/LU-3007344
date created
2012-10-05 11:30:44
date last changed
2012-10-08 10:38:47
@phdthesis{3007344,
  abstract     = {The veal industry is specialized in rearing male calves on a low iron milk diet, hereby obtaining white meat. As in other food animals, high levels of antimicrobial resistance have recently been detected in bacteria from veal calves, potentially threatening treatment options in both human as veterinary medicine. This worrisome observation is currently overwhelming veterinary medicine and revisions of current treatment practices (benchmarking) and the prudent use of antimicrobials in food animals are highly recommended by the European authorities. 
As a general introduction (Chapter 1.1.), an overview of the typical characteristics and challenges of the Belgian white veal industry is given. A synthesis of the current knowledge on antimicrobial resistance in pathogenic, zoonotic and commensal bacteria from veal calves is provided. Bovine respiratory disease (BRD) is the leading cause of morbidity and mortality in young animals in almost every cattle production system worldwide. BRD is a multifactorial disease resulting from the complex interaction of pathogens with host factors (immunity) and the environment, and is therefore also termed bovine respiratory disease complex (BRDC). The BRDC differs in between production systems, and knowledge on the epidemiology and pathogenesis of BRD in each production system is necessary, in order to determine effective control measures for that particular production system. In chapter 1.2. an overview of the constitution of the BRDC in veal calves is given. From this literature review it could be concluded that, under the current organization of the industry, veal calves are at ultra-high risk of developing BRD, making antimicrobial use necessary to overcome disease. Hardly any information on the pathogens involved in the BRDC of veal calves is available.  
For economic reasons and due to a lack of epidemiological knowledge on diseases in veal calves, veterinarians have been tied to empiric, often blind, treatment in the veal industry for decades. In line with this problematic situation and with the emergence of antimicrobial resistance, the overall objective of this doctoral thesis was to gain insights into current practices, into the epidemiology of morbidity and mortality in the Belgian white veal industry and into the underlying pathogens of respiratory disease (Chapter 2). This to provide the industry with objective data from where to install and evaluate sustainable preventive and therapeutic protocols, using less antimicrobials, in the future.  
At present, no information on drug use in white veal calves in Belgium is available. Therefore, the first objective was to document antimicrobial and anti-inflammatory drug use in the Belgian veal industry (Chapter 3). A prospective study was installed, monitoring group and individual drug use on 15 veal cohorts in Belgium. Treatment incidences (TI) based on animal defined daily dose (ADD), prescribed daily dose (PDD) and used daily dose (UDD) were calculated. Antimicrobial drug use was highly intensive, with on average 416.8 ADD per 1000 animals at risk. Antimicrobial drug use consisted for 95.8\% of oral group treatments, and only for 4.2\% of individual administrations. BRD was the main indication for both group (53.0\%) and individual drug use. The most frequently used antimicrobials (group treatments) were oxytetracycline (23.7\%), amoxicillin (18.5\%), tylosin (17.2\%) and colistin (15.2\%). Deviations from the leaflet recommendations were frequently encountered, with 47.3\% of the group treatments underdosed (predominantly oxytetracycline and tylosin to treat dysbacteriosis). Based on the UDD, smaller integrations (less than 50 herds) used more antimicrobials than larger ones. Producers used higher dosages in group treatments than prescribed by the veterinarian in cohorts with a single caretaker. A large variety of antimicrobial compounds were used for individual treatments, including the critically important cephalosporins (8.0\%) and fluoroquinolones (12.6\%). Individual treatments were generally overdosed. Anti-inflammatory drugs were far less frequently used (TIUDD= 5.94), mostly sodium salicylic acid in group treatments. Individually administered anti-inflammatory drugs were generally overdosed. The main conclusion was that antimicrobial drug use is highly intensive at present and that future reduction can only be achieved by reducing the number of oral group treatments.
In a second study (Chapter 4.1.), the objective was to determine the causes and epidemiology of morbidity and mortality in dairy, beef and crossbred white veal production in Belgium. A total of 5853 calves, housed in 15 production cohorts (5 per breed), were followed during one production cycle. Causes of mortality were determined by necropsy. Morbidity was daily recorded by the producers. The total mortality risk was 5,3\% and was significantly higher in beef veal production compared to dairy or crossbreds. The main causes of mortality were pneumonia (1.3\% of the calves at risk), ruminal disorders (0.7\%), idiopathic peritonitis (0.5\%), enterotoxaemia (0.5\%) and enteritis (0.4\%). Idiopathic peritonitis was identified as a disease of unknown origin, specifically occurring around 8-10 weeks after arrival. Belgian Blue beef calves were more likely to die from pneumonia, enterotoxaemia and arthritis. Detection of bovine viral diarrhea virus (BVDV) at necropsy was associated with chronic pneumonia and pleuritis. Of the calves, 25.4\% was treated individually and the morbidity rate was 1.7 cases per 1000 calf days at risk. The incidence rate of respiratory disease, diarrhea, arthritis and otitis was 0.95, 0.30, 0.11 and 0.07 cases per 1000 calf days at risk, respectively. Morbidity peaked in the first three weeks after arrival and gradually declined towards the end of the production cycle. BRD already occurred immediately after arrival, but peaked 3 weeks after arrival. A long tail in the treatment curve was observed, associated with chronic pneumonia (relapse rate= 10.2\% on average). It could be concluded that, whereas the group of digestive diseases was responsible for most mortalities, BRD was the single leading cause. BRD was also the main cause of morbidity, and a long tail of chronic disease, associated with BVDV at necropsy, was observed. 
Next, the impact of BRD, diarrhea, otitis and arthritis on mortality and carcass traits was studied in a sample of 3519 white veal calves (10 cohorts) (Chapter 4.2.). Disease registration was based on individual treatment by the producer and cause of death was determined by necropsy. Carcass data (hot carcass weight (HCW), color and fatness degree) were obtained from the slaughter houses. Average daily gain (ADG), carcass value (CV) and CV reduced by treatment costs were calculated. In comparison to non-treated calves, calves treated once for BRD showed a 0.066 kg/day reduction in ADG and 8.2 kg reduction of HCW, had a lower carcass value, a lower fatness degree and an increased mortality risk. The reduction in ADG, HCW, CV, fatness degree and the mortality risk increased dramatically with increasing number of BRD treatments. Calves treated multiple times for BRD also had higher odds for low carcass quality and were more likely to be classified as too red meat for white veal production. Arthritis increased the mortality risk, but reduced HCW only when associated with BRD. Otitis did not affect any of the studied parameters. Diarrhea increased the mortality risk, reduced ADG and HCW by 0.078 kg/day and 8.8 kg, respectively, and decreased carcass quality. It could be concluded that even under intensive coverage by oral antimicrobial group treatments, substantial economic losses occur in calves, which require individual treatment for BRD, diarrhea or arthritis. Controlling calf health by effective preventive and therapeutic strategies and in particular the prevention of chronic BRD is key for the profitability of veal operations.
Because of the importance of BRD in morbidity, mortality and the associated drug use, further focus was on the identification of the pathogens involved in the BRDC of white veal calves in Belgium. 
In a fourth study (Chapter 5.1.), the prevalence of respiratory pathogens in diseased, unvaccinated, routinely medicated veal calves was determined, by sampling 24 natural outbreaks of BRD in Belgium (15 herds). Bacteria were cultured from nasopharyngeal swabs and seroconversion against viruses and Mycoplasma bovis was determined on paired sera. The inclusion criterion for sampling, was 10\% of the animals with respiratory symptoms. Most outbreaks (75\%) occurred between week 2 and 4 after arrival. In 54.2\% of the outbreaks (13/24), antimicrobial group treatments for BRD had already been installed before the sampling criterion was reached, and in 29.2\% (7/24) calves were still receiving oral antimicrobials at sampling. At the individual calf level, Mycoplasma spp., Mannheimia haemolytica and Pasteurella multocida were retrieved from 70.5\%, 21.5\% and 26.0\% of the swabs, respectively. At the herd level the presence of M. bovis could be confirmed on 84.6\% of the examined herds. Serological evidence of  BVDV, parainfluenzavirus type 3 (PI-3), bovine respiratory syncytial virus (BRSV), bovine adenovirus 3 (BAV-3), bovine coronavirus (BCV) and bovine herpesvirus 1 (BHV-1) infection was present on 71.4\%, 53.3\%, 40.0\%, 46.7\%, 30.0\% and 26.7\% of the herds, respectively. At necropsy, Mycoplasma spp. could be cultured from 61.9\% of pneumonic lungs (n=21) and respectively 60.0\% and 20.0\% of the tested calves were BVDV (n=20) and BRSV (n=16) PCR positive. It can be concluded that BRD in white veal calves is of slow progressive nature rather than massive acute outbreaks, likely due to the presence of maternal immunity and the frequently applied metaphylactic antimicrobial therapy. Under such conditions the peak incidence is reached on average at week 3 post arrival. At that time, next to a variable viral component in the individual calf, (multi)resistant Pasteurellaceae are prevalent. Overall, M. bovis and BVDV appear to play an important role in both the initiation of BRD (acute outbreak) as in lethal chronic cases. 
In a final study (Chapter 5.2.), the seroepidemiology of respiratory infections along the white veal production cycle and their association with BRD and carcass traits was determined. Also, the potential value of total and respiratory pathogen specific antibody levels at arrival to predict subsequent BRD and suboptimal carcass traits was evaluated. A total of 467 calves, housed in 15 veal herds, were sampled at arrival and 6, 12 and 24 weeks later. Antibody levels to 7 respiratory pathogens were determined at each time point by semi-quantitative ELISA. Circulation of PI-3, BAV-3 and M. bovis was detected in all studied herds. For BVDV, BRSV, BHV-1 and M. haemolytica 93.3\% (13/15), 80.0\% (12/15), 53.3\% (8/15) and 86.7\% (13/15) of the herds were infected, respectively. The respiratory disease peak in the first 6 weeks after arrival was associated with seroconversion to M. bovis (44.2\% of the calves) and BVDV (32.0\%). More than 50\% of the calves seroconverted to at least one virus in this period, whereas seroconversion to M. haemolytica was not associated with the BRD peak. The prevalence of calves, persistently (PI) and transiently infected with BVDV, was 0.6\% and 1.5\%, respectively. PI calves had very low survival chances. With exception of M. bovis (10,7\% of the calves on average), maternal antibodies were abundantly present at arrival for most pathogens, with little variation between herds. A worrisome 40.1\% of the calves on average, ranging from 24.0 to 59.9\%, had low total IgG levels at arrival, suggesting failure of passive transfer. Calves, seropositive to PI-3 and M. bovis at arrival, had a decreased and increased risk for BRD, respectively. Low ({\textlangle}8g/L) total IgG at arrival tended towards an increased BRD risk. No associations with carcass traits were found. Under the current medical management, the serostatus for respiratory pathogens at arrival was of little practical use to classify veal calves according to BRD risk or to predict carcass traits. To help improve the validity of epidemiological studies in the veal industry, standard case definitions should be provided and group antimicrobial treatments avoided. 
In the general discussion (Chapter 6), first, the value of the applied study methodology for veal calf health monitoring systems and future holistic studies is discussed. With the obtained insights into the epidemiology of veal calf diseases (predominantly BRD) in mind, the general discussion mainly aimed at critically reflecting on the current (medical) management practices. A series of possible short and long term measures to control BRD and reduce antimicrobial use, to be evaluate in the future, is proposed.
Overall, it could be concluded that BRD is the main cause of morbidity and mortality in veal calves and subsequently the main indication for the highly intensive drug use in the Belgian veal industry. Despite the frequent antimicrobial coverage, the economic consequences of disease in calves requiring individual treatment were devastating. Almost every BRD pathogen was present on each herd, with a viral component in over 50\% of the calves. Overall M. bovis and BVDV were most prevalent in acute and chronic BRD in white veal calves. The high prevalence of calves with insufficient levels of IgG at arrival is worrisome and requires attention at the herds of origin. Both the applied monitoring techniques as the obtained results can guide the veal industry in their search for evidence based preventive and therapeutic protocols, reducing antimicrobial use, while maintaining production results and animal welfare standards. More in specific, modifying current medical management towards M. bovis, exclusion of PI animals from veal production, vaccination and optimization of maternal immunity might be beneficial measures to reduce the BRD incidence and herewith associated antimicrobial use in veal calves.},
  author       = {Pardon, Bart},
  isbn         = {9789058643087},
  keyword      = {antimicrobial use,drug use,mortality,morbidity,veal,BRD},
  language     = {eng},
  pages        = {316},
  publisher    = {Ghent University. Faculty of Veterinary Medicine},
  school       = {Ghent University},
  title        = {Morbidity, mortality and drug use in white veal calves with emphasis on respiratory disease},
  year         = {2012},
}

Chicago
Pardon, Bart. 2012. “Morbidity, Mortality and Drug Use in White Veal Calves with Emphasis on Respiratory Disease”. Merelbeke, Belgium: Ghent University. Faculty of Veterinary Medicine.
APA
Pardon, B. (2012). Morbidity, mortality and drug use in white veal calves with emphasis on respiratory disease. Ghent University. Faculty of Veterinary Medicine, Merelbeke, Belgium.
Vancouver
1.
Pardon B. Morbidity, mortality and drug use in white veal calves with emphasis on respiratory disease. [Merelbeke, Belgium]: Ghent University. Faculty of Veterinary Medicine; 2012.
MLA
Pardon, Bart. “Morbidity, Mortality and Drug Use in White Veal Calves with Emphasis on Respiratory Disease.” 2012 : n. pag. Print.