Epidemiologiske studier av bovint respiratorisk syncytialvirus og bovint coronavirus i Norge

Bovine respiratory syncytial virus (BRSV) and bovine coronavirus (BCV) cause respiratory infection in cattle worldwide. In addition, BCV also causes diarrhoea in calves and contagious diarrhoea in adult cows, i.e. winter dysentery. The occurrence is endemic in the Norwegian cattle population, and the planning of a national control programme against these viral infections prompted the need for more research focused at the herd level. The overall objective of this thesis was to provide knowledge about the epidemiology of BRSV and BCV in the Norwegian cattle population, as a scientific basis for systematic control work. To reach this aim, we utilized register data, bulk tank milk antibody testing and reports of disease outbreaks. A risk factor analysis showed that large herd size and short distance to neighbours were associated with increased odds of antibody positivity in bulk tank milk for both viruses. Purchase of livestock was an additional risk factor for BCV. Spatial analysis revealed geographic differences in the distribution of prevalence. A cohort study was performed based on a regional outbreak of winter dysentery. The estimated drop in milk production was 3.6 L/cow at maximum, or 15% for the average herd, showing a notable effect of winter dysentery on milk production at the herd level. The MVD-Enferplex BCV/BRSV multiplex immunoassay was developed to screen herds for antibodies in bulk tank milk. A diagnostic test evaluation was performed for this application, by comparing it to two commercially available ELISAs, using Bayesian latent class models. Adjusting the configuration and cut-off values of the test resulted in acceptable sensitivity and specificity for both BRSV and BCV. A framework for herd-level calculations of probability of freedom (PostPFree) from BRSV and BCV antibodies over time was developed by use of bulk tank milk testing, geographic information and animal movement data. PostPFree was updated every three months, and validation against a subsequent bulk tank milk sample after three years showed that it provided an improved estimate of a herd’s antibody status compared to relying on the previous test result. Altogether, the results have provided insights at the herd level regarding: risk factors for a positive classification, consequences of disease and the uncertainty of herd classification. This knowledge can be directly applied in systematic control work.Bovint respiratorisk syncytialvirus (BRSV) og bovint coronavirus (BCV) er årsak til luftvegslidelser hos storfe over hele verden. I tillegg kan BCV også forårsake kalvediaré og smittsom diaré hos voksne storfe, kalt vinterdysenteri. Forekomsten er endemisk i den norske storfepopulasjonen, og planleggingen av et nasjonalt kontrollprogram mot disse virusinfeksjonene skapte behov for mer forskning på besetningsnivå. Det overordnede målet med avhandlingen var å generere kunnskap om epidemiologien til BRSV og BCV i den norske storfepopulasjonen, som et bidrag til forskningsbasert, systematisk kontrollarbeid. For å nå dette målet brukte vi registerdata, tankmelk-serologi, og rapportering av sykdomsutbrudd. En risikofaktoranalyse viste at store besetninger og kort avstand til nabogårder, var assosiert med økt odds for antistoffpositivitet i tankmelk for begge virus. I tillegg var kjøp av livdyr en risikofaktor for BCV. Romlig statistisk analyse avdekket geografiske forskjeller i fordelingen av prevalens. En kohortstudie basert på et regionalt utbrudd av vinterdysenteri viste at det estimerte tapet i melkeproduksjon var 3,6 L/ku på det meste, eller 15% for en gjennomsnittsbesetning. Dette viser at vinterdysenteri har en betydelig effekt på besetningens melkeproduksjon. En nyutviklet MVD-Enferplex BCV/BRSV multiplex immunoassay har blitt brukt til screening av besetninger for antistoffer i tankmelk. Testen ble evaluert for denne anvendelsen ved å sammenligne den med to kommersielt tilgjengelige ELISA-tester, i Bayesianske latent klasse modeller. Multiplex testen kan, ved å endre konfigurering og cut-off verdier, oppnå akseptabel sensitivitet og spesifisitet for både BRSV og BCV. En metode for å beregne en besetnings sannsynlighet for frihet (PostPFree) fra BRSV og BCV antistoffer over tid ble utviklet ved å inkludere tankmelk-testing, geografisk informasjon og dyreforflytninger. PostPFree ble oppdatert hver tredje måned, og ved validering mot ny tankmelktest etter tre år gav den bedre estimater for besetningers antistoffstatus enn det man fikk bare basert på forrige prøvesvar. Alt i alt har resultatene gitt mer kunnskap på besetningsnivå om: risikofaktorer for positiv klassifisering, konsekvenser av sykdom og usikkerheten rundt klassifisering av besetninger. Denne kunnskapen har direkte anvendelse i systematisk kontrollarbeid

Epidemiologic studies of bovine respiratory syncytial virus and bovine coronavirus in Norway

Bovine respiratory syncytial virus (BRSV) and bovine coronavirus (BCV) cause respiratory infection in cattle worldwide. In addition, BCV also causes diarrhoea in calves and contagious diarrhoea in adult cows, i.e. winter dysentery. The occurrence is endemic in the Norwegian cattle population, and the planning of a national control programme against these viral infections prompted the need for more research focused at the herd level. The overall objective of this thesis was to provide knowledge about the epidemiology of BRSV and BCV in the Norwegian cattle population, as a scientific basis for systematic control work. To reach this aim, we utilized register data, bulk tank milk antibody testing and reports of disease outbreaks. A risk factor analysis showed that large herd size and short distance to neighbours were associated with increased odds of antibody positivity in bulk tank milk for both viruses. Purchase of livestock was an additional risk factor for BCV. Spatial analysis revealed geographic differences in the distribution of prevalence. A cohort study was performed based on a regional outbreak of winter dysentery. The estimated drop in milk production was 3.6 L/cow at maximum, or 15% for the average herd, showing a notable effect of winter dysentery on milk production at the herd level. The MVD-Enferplex BCV/BRSV multiplex immunoassay was developed to screen herds for antibodies in bulk tank milk. A diagnostic test evaluation was performed for this application, by comparing it to two commercially available ELISAs, using Bayesian latent class models. Adjusting the configuration and cut-off values of the test resulted in acceptable sensitivity and specificity for both BRSV and BCV. A framework for herd-level calculations of probability of freedom (PostPFree) from BRSV and BCV antibodies over time was developed by use of bulk tank milk testing, geographic information and animal movement data. PostPFree was updated every three months, and validation against a subsequent bulk tank milk sample after three years showed that it provided an improved estimate of a herd’s antibody status compared to relying on the previous test result. Altogether, the results have provided insights at the herd level regarding: risk factors for a positive classification, consequences of disease and the uncertainty of herd classification. This knowledge can be directly applied in systematic control work

A Descriptive Study of Keel Bone Fractures in Hens and Roosters from Four Non-Commercial Laying Breeds Housed in Furnished Cages

The keel bone in birds is an extension of the sternum. Fractures to the keel are common in modern laying hen breeds. Several of the proposed causal mechanisms behind keel bone fractures (KBF) are linked to selection for efficient production. It is, therefore, of interest to explore whether less selected breeds have a lower occurrence of keel bone fractures compared to reports from highly selected, modern laying hen breeds. Thus, the aim of the current study was to investigate keel bones of hens from four non-commercial layer breeds. Birds were housed in furnished cages and keel bones examined at 30 and 63 weeks of age using a portable X-ray equipment. The results from this descriptive study indicate a low prevalence of keel bone fractures in hens at both ages in all four breeds. No fractures were observed in the examined roosters. The overall low numbers of fractures indicate that genetic factors may be involved and, thus that selective breeding may help to reduce the susceptibility to keel bone fractures. Finally, this study highlights the importance of poultry conservation to secure existing genetic diversity, which may be an important resource in future selection schemes.publishedVersio

Mortality risk on farm and during transport: a comparison of 2 broiler hybrids with different growth rates

ABSTRACT: Mortality in broilers is often associated with poor health and welfare and has a complex and multifactorial etiology. Recent studies under experimental conditions indicated that genetic selection for fast growth is an important risk factor for mortality in broiler chickens. However, the knowledge on broiler mortality in general, and in slower growing broilers in particular, under commercial conditions is still limited. This retrospective cohort study aimed to describe mortality risk on farm and during transport in 2 broiler hybrids with different growth rates, Ross 308, and Hubbard JA787, and to estimate the association between hybrid and mortality at different stages of the production cycle. The study sample consisted of 64,651,804 broilers from 4,228 flocks and 139 farms slaughtered from January 1st, 2015, to June 22nd, 2021. Analysis of on-farm mortality was restricted to broiler flocks slaughtered in the period July 2017 to July 2018 due to changes known to affect FWM. The effect of hybrid on mortality during 3 different production stages (first week mortality (FWM), mortality after the first week (MAFW), and mortality during transport (DOA)), was assessed using mixed effect negative binomial regression models. Descriptively, there were notable differences in mortality at all stages of the production cycle, with higher mean mortalities in Ross 308 (1.40% FWM, 3.05% MAFW, and 0.063% DOA) than in Hubbard JA787 (0.76% FWM, 1.49% MAFW, and 0.015% DOA). In the analysis, the largest estimated difference was found for dead on arrival under cold conditions, where mortality was almost 5 times higher in Ross 308 compared to Hubbard JA 787 (IRR: 4.70, 95% CI: 3.74–5.90). The estimated difference in FWM between hybrids was highest during autumn, with an estimated risk approximately 1.6 times higher in Ross than in Hubbard (IRR: 1.56, 95% CI: 1.30–1.86). For MAFW, the estimated risk was approximately 2 times higher in Ross than in Hubbard (IRR: 2.13 95% CI: 1.82–2.49). The findings in this study emphasize the need for more knowledge on causes of mortality in broilers including effects of genetic factors as basis for preventive measures

Using Biosecurity Measures to Combat Respiratory Disease in Cattle: The Norwegian Control Program for Bovine Respiratory Syncytial Virus and Bovine Coronavirus

Bovine respiratory disease (BRD) cause important health problems in all cattle husbandry systems. It contributes substantially to the use of antimicrobial substances and compromises animal welfare and the sustainability of the cattle industry. The existing preventive measures of BRD focus at the individual animal or herd level and include vaccination, mass treatment with antimicrobials and improvement of the animal's environment and general health status. Despite progress in our understanding of disease mechanism and technological development, the current preventive measures are not sufficiently effective. Thus, there is a need for alternative, sustainable strategies to combat the disease. Some of the primary infectious agents in the BRD complex are viruses that are easily transmitted between herds such as bovine respiratory syncytial virus (BRSV) and bovine coronavirus (BCoV). This conceptual analysis presents arguments for combatting BRD through improved external biosecurity in the cattle herds. As an example of a population-based approach to the control of BRD, the Norwegian BRSV/BCoV control-program is presented. The program is voluntary and launched by the national cattle industry. The core principle is classification of herds based on antibody testing and subsequent prevention of virus-introduction through improved biosecurity measures. Measures include external herd biosecurity barriers and regulations in the organization of animal trade to reduce direct and indirect transmission of virus. Improved biosecurity in a large proportion of herds will lead to a considerable effect at the population level. Positive herds are believed to gain freedom by time if new introduction is avoided. Vaccination is not used as part of the program. Dissemination of information to producers and veterinarians is essential. We believe that reducing the incidence of BRD in cattle is essential and will lead to reduced antimicrobial usage while at the same time improving animal health, welfare and production. Alternative approaches to the traditional control measures are needed