Now showing 1 - 4 of 4
  • Publication
    Risk factors associated with exposure to bovine respiratory disease pathogens during the peri-weaning period in dairy bull calves
    Background: Bovine respiratory disease (BRD) remains among the leading causes of death of cattle internationally. The objective of this study was to identify risk factors associated with exposure to BRD pathogens during the peri-weaning period (day (d)-14 to d 14 relative to weaning at 0) in dairy bull calves using serological responses to these pathogens as surrogate markers of exposure. Clinically normal Holstein-Friesian and Jersey breed bull calves (n=72) were group housed in 4 pens using a factorial design with calves of different breeds and planes of nutrition in each pen. Intrinsic, management and clinical data were collected during the pre-weaning (d-56 to d-14) period. Calves were gradually weaned over 14 days (d-14 to d 0). Serological analysis for antibodies against key BRD pathogens (BRSV, BPI3V, BHV-1, BHV-4, BCoV, BVDV and H. somni) was undertaken at d-14 and d 14. Linear regression models (for BVDV, BPI3V, BHV-1, BHV-4, BCoV and H. somni) and a single mixed effect random variable model (for BRSV) were used to identify risk factors for changes in antibody levels to these pathogens. Results: BRSV was the only pathogen which demonstrated clustering by pen. Jersey calves experienced significantly lower changes in BVDV S/P than Holstein-Friesian calves. Animals with a high maximum respiratory score (≥8) recorded significant increases in H. somni S/P during the peri-weaning period when compared to those with respiratory scores of ≤3. Haptoglobin levels of between 1.32 and 1.60 mg/ml at d-14 were significantly associated with decreases in BHV-1 S/N during the peri-weaning period. Higher BVDV S/P ratios at d-14 were significantly correlated with increased changes in serological responses to BHV-4 over the peri-weaning period. Conclusions: Haptoglobin may have potential as a predictor of exposure to BHV-1. BRSV would appear to play a more significant role at the 'group' rather than 'individual animal' level. The significant associations between the pre-weaning levels of antibodies to certain BRD pathogens and changes in the levels of antibodies to the various pathogens during the peri-weaning period may reflect a cohort of possibly genetically linked 'better responders' among the study population.
    Scopus© Citations 21  307
  • Publication
    First confirmation by PCR of Jaagsiekte sheep retrovirus in Ireland and prevalence of ovine pulmonary adenocarcinoma in adult sheep at slaughter
    Background: Ovine pulmonary adenocarcinoma (OPA), caused by Jaagsiekte sheep retrovirus (JSRV), is characterised by the development of invariably fatal lung tumours primarily in adult sheep. High infection rates and disease prevalence can develop during initial infection of flocks, leading to on-farm economic losses and animal welfare issues in sheep with advanced disease. The disease has been reported in Ireland and is notifiable, but the presence of JSRV has never been confirmed using molecular methods in this country. Additionally, due to the difficulties in ante-mortem diagnosis (especially of latently-infected animals, or those in the very early stages of disease), accurate information regarding national prevalence and distribution is unavailable. This study aimed to confirm the presence of JSRV in Ireland and to obtain estimates regarding prevalence and distribution by means of an abattoir survey utilising gross examination, histopathology, JSRV-specific reverse transcriptase polymerase chain reaction (RT-PCR) and SU protein specific immunohistochemistry (IHC) to examine the lungs of adult sheep. Results: Lungs from 1911 adult sheep were examined macroscopically in the abattoir and 369 were removed for further testing due to the presence of gross lesions of any kind. All 369 were subject to histopathology and RT-PCR, and 46 to IHC. Thirty-one lungs (31/1911, 1.6%) were positive for JSRV by RT-PCR and/or IHC but only ten cases of OPA were confirmed (10/1911, 0.5%) Four lung tumours not associated with JSRV were also identified. JSRV-positive sheep tended to cluster within the same flocks, and JSRV-positive sheep were identified in the counties of Donegal, Kerry, Kilkenny, Offaly, Tipperary, Waterford and Wicklow. Conclusions: The presence of JSRV has been confirmed in the Republic of Ireland for the first time using molecular methods (PCR) and IHC. In addition, an estimate of OPA prevalence in sheep at slaughter and information regarding distribution of JSRV infection has been obtained. The prevalence estimate appears similar to that of the United Kingdom (UK). Results also indicate that the virus has a diverse geographical distribution throughout Ireland. These data highlights the need for further research to establish national control and monitoring strategies.
    Scopus© Citations 14  370
  • Publication
    An approach to diagnosis of Jaagsiekte sheep retrovirus infection in sheep based on assessment of agreement between macroscopic examination, histopathologic examination and reverse-transcriptase polymerase chain reaction
    Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma (OPA). JSRV infection is usually detected post-mortem by macroscopic and histological examination of lungs for lesions of OPA. Subsequently, the presence of JSRV may be confirmed using polymerase chain reaction (PCR) on tumour tissue. Our goal was to determine the most effective way of combining macroscopic and histological examination with reverse transcriptase PCR (RT-PCR) to detect JSRV infection post-mortem. Lungs of slaughtered sheep (n = 369) with macroscopic lesions were examined macroscopically and histologically to identify lesions consistent with OPA, and subsequently subjected to RT-PCR for JSRV. Positive (Ppos) and negative (Pneg) agreement and Cohen’s Kappa were calculated between RT-PCR and: 1) macroscopic examination; 2) histological examination; 3) macroscopic and histological examinations combined in series, and 4) in parallel. The highest Ppos was between macroscopic and histological examination in parallel and RT-PCR (0.38). Conversely, Pneg for all combinations of RT-PCR and macroscopic and histological examinations was high (0.95-0.96). All Kappa values were low (0.1-0.33). This indicates that macroscopic and histological examination combined in parallel is the most effective way to identify animals that should be tested using RT-PCR for JSRV. If a positive result is obtained on macroscopic examination and/or histological examination, RT-PCR for JSRV should be carried out. The high Pneg indicates that if a negative result is obtained on macroscopic and histological examination, RT-PCR testing is not merited, as the result is likely to be negative. This provides an evidence-base for the diagnosis of JSRV infection.
    Scopus© Citations 2  356