Ontario Animal Health Network (OAHN) Bovine Expert Network Quarterly Veterinary Report

Global Surveillance Update:
Influenza A (H5N1) detected in livestock in the United States of America

Spillover of Influenza A (H5N1) into U.S. livestock was first reported in March 2024 and continues to evolve. Initially a goat kid in Minnesota tested positive for highly pathogenic avian influenza (HPAI) followed by an announcement from USDA that H5N1 had been detected in milk from ill dairy cattle.

The Ontario Animal Health Network will keep their page up to date with new resources as available at: H5N1 Detections In U.S. Livestock 2024 – Ontario Animal Health Network (oahn.ca).


Updates from the U.S. Department of Agriculture – Animal and Plant Health Inspection Service

Updates from the Canadian Food Inspection Agency (CFIA)

Q4 Bovine Data from the Animal Health Laboratory

A total of 1554 bovine cases were submitted to the AHL during Q4, spanning from November 1 2023 to January 31 2024. Of these, 147 submissions had a pathology component, consisting of 51 postmortem cases and 97 send-in cases (including 35 meat inspection cases). Of these, there were 26 reproductive loss investigations, 20 young calves (under 2 months of age), 24 older calves (2 months to 2 years of age) and 42 adult cattle. Submissions from practitioners included 69 dairy, 31 beef, and 11 where the commodity was not specified. Insufficient clinical history was associated with 3 submissions

Pathology Cases of Interest

Case 1: Methicillin-resistant Staphylococcus aureus in a Holstein calf

History: 1-month-old Holstein calf, never thrifty, treated for pneumonia for several weeks.

Pathology: Microscopic examination confirmed the presence of subacute fibrinosuppurative pneumonia typical of a bacterial cause, and a mild chronic interstitial nephritis compatible with an embolic bacterial etiology, such as that caused by E. coli (e.g., white spotted kidney).

Ancillary testing: Bacterial culture of lung and pooled filter organs (liver/spleen/kidney) both isolated 1+ Methicillin-resistant S. aureus,

and Streptococcus ruminatium was also isolated from lung. The respiratory PCR panel did not detect BoHV-1. PI-3 or BRSV in lung.

Summary: Bacterial culture was likely influenced by the several week treatment for pneumonia, so involvement of primary respiratory bacterial pathogens not isolated at this point was suspected, and given the protracted nature of the pneumonia, the possibility of initial viral involvement couldn’t be excluded. Methicillin-resistant S. aureus is a zoonotic pathogen that can cause infections in people, and isolation of this pathogen is also a reminder to engage in discussions regarding prudent antimicrobial use on-farm. A quick review of the AHL database found only 3 previous isolations of MRSA from bovine specimens: two in 2017 (milk samples from same cow) and one in 2015 (slaughter sample).

Case 2: Bovine coronavirus in bovine respiratory disease in calves

History: Poor-doing calves with ‘no clinical signs’ prior to death. Recently stopped vaccinating calves for coronavirus. May have been treated with antibiotics.

Pathology: Microscopic lesions in lung support bacterial pneumonia with possible viral infection, as there was some evidence of bronchiolar epithelial injury. This epithelial lesion can develop in the face of viral injury or in the face of robust neutrophilic luminal exudates.

Ancillary testing: Mannheimia haemolytica was isolated in large numbers from lung. To investigate for the presence of viral antigens, PCR testing was performed on lung, and while this did not detect BoHV-1, BRSV, PI-3 or adenovirus, bovine coronavirus was detected. Subsequent immunohistochemistry was performed to assess for bovine coronavirus antigen in histologic section, and it was not detected; however, this may reflect the lower sensitivity of the test compared with PCR methods, and bovine coronavirus may have played a role in the development of pneumonia in this case.


In total, 181 bovine submissions had bacterial culture performed (non-milk), generating 272 cultures. Salmonella spp. were isolated from 5 submissions, representing an estimated 3 premises.

Salmonella Dublin was isolated from all 5 submissions, all with no record of previous isolation of this pathogen at the premises.

  • Two were semen samples sent for bacterial culture (no history provided).
  • Two were swabs from a herd with a clinical history of pneumonia and increased mortality in 4- to 10-week-old dairy calves.
  • One was a kidney sample from a herd with an increase in pneumonia and mortality in dairy cattle.

In total, 20 bovine submissions had Salmonella Dublin PCR performed. Of the 25 tissues tested, there were two detections from two different premises.

  • 3-month-old Holstein dairy calf with septicemia characterized by fibrinosuppurative enterocolitis, splenitis and pneumonia
  • 3-month-old Holstein dairy calf (veal) with pneumonia and diarrhea

Bovine Viral Diarrhea Virus (BVDV)

In total, 66 submissions generated 167 samples for BVDV PCR testing, yielding 6 positive samples from one submission (herd screening). BVDV immunohistochemistry was not performed for any pathology submissions.

About This Report
This summary has been compiled by Dr. Rebecca Egan, Animal Health Laboratory (AHL) from diagnostic submissions to the AHL Guelph and Kemptville locations.

Salmonella Dublin Update

Laboratory Data 2023

During 2023, 20 lab diagnostic submissions to the AHL detected Salmonella Dublin on bacterial culture or PCR test (Figure 1) plus an additional 12 research submissions. The submissions are estimated to represent 16 separate on farm outbreaks of disease from 14 different farms. For 9 farms, this was their first diagnosis of S. Dublin (Figure 2). This compares to 23 outbreaks and 13 first premises diagnoses in 2022.

As of December 31, 2023, there are estimated to be 100 unique premises in the laboratory dataset that have had S. Dublin, of which 38 are veal, 55 are dairy, and 7 are from a beef operation.

Salmonella Dublin (Individual and Bulk) ELISA Testing

All Salmonella Dublin ELISA testing  is summarized in the Ontario Interactive Animal Pathogen Dashboards (IAPD). For access to the dashboards, visit https://iapd.lsd.uoguelph.ca/. All Ontario veterinary clinics are eligible for a unique login.

S. Dublin Journal Articles of Interest:

OAHN Mastitis Report

2023 Mastitis PCR Test Data for Ontario Lactanet Herds

Summary provided by Dr. David Kelton, OVC in collaboration with Lactanet

2023 Ontario Mastitis PCR Summary Number of Samples Percent of Samples Group Avg SCC (x1000)
Staph aureus POS 1191 12.0% 1234
S aureus HIGH POS 116 9.740% 3147
S aureus MOD POS 487 40.89% 1528
S aureus LOW POS 588 49.37% 608
Strep ag POS 6 0.06% 575
Mycoplasma POS 13 0.13% 3409
Prototheca POS 162 1.63% 1143
NEG to all 4 pathogens 8571 86.32% 1063
Total 9929 1088

Interpretation Notes

  • While 12% of samples were positive for Staph aureus, less than 10% were HIGH positive
  • For Staph aureus cows, SCC is correlated with PCR result, as expected
  • Caution: Low positive Staph aureus tests might not be infected – check SCC
  • Only 6 samples positive for Strep agalactiae

Mastitis Pathogens from Milk Cultures Submitted to the Animal Health Laboratory in 2023 (using MALDI-TOF)

Summary provided by Dr. Tanya Rossi and Dr. Durda Slavic

Ontario Bovine Disease Surveillance

Bovine disease surveillance in Ontario is a collaborative effort involving many public and private stakeholders. Diagnostic results generated by veterinary laboratories, clinical impression and case data provided by bovine veterinarians, disease detections reported outside of Ontario, and research projects facilitated by Academic institutions or the Ontario Animal Health Network (OAHN), are all key sources of surveillance data. Strong communication between these stakeholders and with dairy, beef, and veal producers supports both cattle and human health in Ontario.

Please follow the links below for additional information on the associated activities or organizations and for many resources useful to bovine industry members.


*Response varies with each disease ranging from case management recommendations to regulatory action.


Bovine Veterinarians

  • Report bovine health situations of serious risk
  • Provide case data to regulatory authorities & disease information to OAHN
  • Share bovine disease communications

Diagnostic Labs

Bovine Industry


Other Government

Other Resources to Check Out

Canadian Animal Health Surveillance System (CAHSS) https://cahss.ca/

A network of animal health surveillance networks in Canada – the CAHSS website includes a variety of resources. Some highlights include:

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NOV 2023 – JAN 2024

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