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

Items of interest from recent bovine expert network meeting:

Cattle Surveillance

There were 138 bovine pathology submissions in Q2, which spanned from May 1 to July 31, 2022.

Adult Cattle

There were 35 submissions (dairy n=20, beef n=12, not specified=3).

PM submissions: 11

Tissue submissions: 24

Pertinent pathology findings included:

  • Pneumonia (M. hemolytica, P. multocida, Bibersteinia trehalosi, M. bovis)
  • Enteritis (coronavirus)
  • Neurologic disease (polioencephalomalacia, listeriosis)
  • Mastitis (E. coli, T. pyogenes)
  • Metritis/endometritis
  • Endocarditis
  • Septicemia (Streptococcus dysgalactiae subsp. equisimilis, idiopathic)
  • Clostridial myositis
  • Eosinophilic myositis (idiopathic)
  • Dermatitis (Staphlococcus aureus)
  • Lymphoma

Older Calves (2 months to 2 years)

There were 23 submissions (dairy n=7, beef n=12, bison=1, not specified=3)

PM submissions: 5

Tissue submissions: 18 (some submissions limited by few histology samples and/or lack of fresh tissue for ancillary testing, hindering ability to reach a diagnosis)

Pertinent pathology findings included:

  • Pneumonia (M. hemolytica, Pasteurella, M. bovis, mycotic, idiopathic interstitial pneumonia*)
  • Enteritis/colitis (coccidia, cryptosporidiosis, idiopathic)
  • Neurologic disease (idiopathic cerebral edema and hemorrhage)
  • Septicemia
  • Clostridial myositis
  • Dermatitis (ringworm)
  • Abomasitis/rumenitis (MCF, mycotic)
  • Omphalitis (mycotic)

Young Calves (< 2 months of age)

There were 43 submissions (dairy n=19, beef n=22, not specified=2).

PM submissions: 8

Tissue submissions: 35

Pertinent pathology findings included:

  • Pneumonia (BRSV, M. hemolytica, Pasteurella, H. somni, Bibersteinia trehalose, M. bovis, T. pyogenes)
  • Enteritis (rotavirus, coronavirus, cryptosporidiosis, coccidiosis, ETEC)
  • Neurologic disease (fibrinosuppurative meningitis)
  • Pericarditis/myocarditis
  • Peritonitis
  • Abomasal ulcer
  • Dermatitis/cellulitis

Abortion/Stillbirth/Premature Birth

There were 22 submissions for abortion investigations (dairy n=21, beef n=1).

Abortion 21 Premature birth
Stillbirth 0 Full term peri-parturient neonatal death

PM submissions: 20

Tissue submissions: 2

Presumptive or definitive diagnosis in 15 cases

  • Idiopathic abortion (n=7)
  • Bacterial (isolates included Bacillus licheniformis, Streptococcus pluranimalium, Campylobacter fetus subsp. fetus)
  • BoHV-1
  • Neospora
  • Ureaplasma
  • Leptospirosis (PCR+ fetal tissue at 5 months gestation from an unvaccinated dairy herd with 10 abortions in 2 months)
  • Malformation/micronutrient – One case with cranioschisis, microencephaly, cerebellar hypoplasia, brachygnathia, necrosuppurativeplacentitis with vasculitis, and relatively low fetal hepatic manganese levels (0.56 ug/g).


In total, 267 bovine submissions had bacterial culture performed (non-milk), generating 380 cultures. Salmonella spp. were isolated from 5 submissions, representing an estimated 5 premises. Salmonella Dublin was isolated from 3 of these submissions, representing approximately 3 premises. Primary findings associated with isolation of S. Dublin (if provided), included pneumonia, arthritis and sudden death.

Bovine Viral Diarrhea Virus

A total of 144 BVDV PCR tests were performed. There was 1 positive result generated from 1 submission, which was a calf that died suddenly due to M. hemolytica pneumonia (vaccinated with Bovishield 3 weeks prior).

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

Probable New Strain of Winter Dysentery – Quebec

The Reseau d’alerte et d’information zoosanitaire (RAIZO) in Quebec reported an outbreak of winter dysentery cases in several Montérégie cattle farms in December 2021. The cases were reported to be more severe and more contagious than what is usually observed with this disease. Subsequently, veterinarians in 6 other regions reported similar cases of severe winter dysentery. Half of the affected farms reported hemorrhagic diarrhea and mortalities in both youngstock and adult cattle. Significant decreases in milk production were reported and some animals required blood transfusions due to the severe hemorrhagic diarrhea. Most cattle recovered within 4-5 days and the outbreaks on farm resolved after about 2 weeks.

Genomic sequencing on one bovine sample collected in 2021 suggests it is highly similar to a sample collected from a tapir at a Quebec zoo where several ruminants and ungulates were affected with dysentery. Sequencing of strains of coronavirus responsible for winter dysentery is not routinely done making comparisons over time unfeasible, but it is likely that a new more virulent and more contagious strain is now in circulation. Ontario bovine practitioners should be aware of the possibility for a similar emergence in Ontario.

A Mannheimia hemolytica outbreak in a lactating dairy herd

Sarah Ferguson, DVM, Smith Falls Veterinary Services

Outbreak Timeline – Week 1

On Friday March 11th 2022, an 85-head freestall dairy client contacted our clinic and reported what he thought was a viral pneumonia outbreak in his herd. He reported a decrease in feed intake and milk production with several coughing adult cows. At this time the producer was only treating the sick animals with anti-inflammatories. Our recommendation was to re-vaccinate as many animals as possible with an intranasal vaccine and treat sick animals with a first line antibiotic. By Sunday March 13th, the producer had 6 dead cows. Four cows died or were euthanized on March 14th, 5 on March 15th, and 7 on March 16th (all mature animals except for one 13-month-old heifer).

Early clinical signs were pyrexia, lethargy and coughing which progressed rapidly to hemorrhagic nasal discharge, respiratory distress and death. Postmortem findings included severe acute fibrinous pleuritis, interlobular fibrin and edema, severely hemorrhagic lung tissue and trachea blocked with blood clots. Nasal swab samples were collected from clinical animals and lung tissue samples from postmortems and sent to the Animal Health Laboratory (AHL) for virology and bacterial culture.

Our initial recommendation of re-vaccinating the herd was not initiated by the producer until March 13/14 and antibiotic treatment for affected animals was not started until March 14/15. Simply based on what vaccine we had

available at the time, all youngstock was given Nasalgen® on March 13 and all heifers/dry cows received Inforce 3® on March 14th. At this time, it was suspected that most of the lactating herd was already sick or exposed. By March 16th, 28 mature cows were being treated with a treatment protocol of 5 days of ceftiofur (Eficur®) and 3 days of ketoprofen (Anafen®). After the sudden death of a mature heifer on March 16, the producer reported that most of the youngstock animals had increased temperatures and occasional animals were lethargic and coughing. We decided to blanket treat all young calves with florfenicol (Nuflor®) and meloxicam (Metacam®) and heifers with long-acting tetracycline(Oxyvet® 200LA) and meloxicam based on herd pneumonia treatment protocols.

On March 18, lab results confirmed Mannheimia haemolytica type 2 cultured from both the nasal swabs and lung tissue. Nasal swab samples had been collected from 5 animals; 3 of these animals cultured 1+ level and never received treatment during the outbreak, however both animals with a 4+ culture developed clinical signs and required antibiotic treatment.

All viral testing from the nasal swabs and lung tissue came back negative for bovine herpesvirus, PI-3, BRSV, adenovirus, coronavirus and BVDV. Nasal swabs were also Mycoplasma bovis negative. Histopathology of lung tissue noted severe acute fibrinohemorrhagic pleuropneumonia, most likely caused by bacterial pneumonia.

Outbreak Aftermath – Week 2 and beyond

In total, 43 out of the remaining 75 live milking and dry cows ended up becoming symptomatic and receiving treatment.

Approximately 50% of these mature animals required a second round of treatment and 7 animals required a third. The majority of the primary cases occurred in the first 2 weeks of the outbreak and the relapses within the following month. Occasional treatment of animals continued into May with the last chronic animal euthanized in early June.

A total of 27 animals died due to Mannheimia hemolytica type 2 pneumonia (MH2), but of the initial 22 dead animals in the first 5 days, only 1 had been treated with antibiotics due to an initial perception of a viral cause by the producer. One cow developed an abomasal ulcer after calving as well as MH2 pneumonia. After receiving 3 rounds of antibiotics, she was euthanized due to poor prognosis. An additional 3 cows were euthanized in the following 1-2 months due to chronic pneumonia symptoms (one of these animals having become severely ill after receiving an intramuscular vaccine) and 1 cow developed severe acute clinical signs leading to death. All but one of the 27 animals were mature milking cows; only one 13 month old heifer was lost directly due to MH2 pneumonia. Of the 26 dead mature animals, 7 were fresh (< 30 DIM), 3 were early lactation (31-90 DIM), 4 mid lactation (91-150 DIM), 11 were over 150 DIM, and 1 was dry.

Two weeks into the pneumonia outbreak, the producer reported the death of a young heifer calf due to severe acute scours, with an additional 2 severely ill calves. Both of these calves were severely dehydrated, no suckle reflex and pyrexic. They were placed on intravenous fluids for 48-72 hours with trimethoprim and sulfadoxine (TMS, Borgal®) and meloxicam  treatment. Only one of these calves survived. A fourth calf had less severe symptoms and received subcutaneous fluid, antibiotic and anti-inflammatory treatment. All 4 of these sick calves were born during the initial acute period of the outbreak and all of their dams had become sick after calving. Due to concern for poor colostrum quality, all subsequent calves born were given powdered colostrum with oral Trishield First Defense® and intranasal Nasalgen® vaccine. During the first couple weeks of the outbreak, newborn calves struggled to thrive and required additional care. On average, nearly all the near-term cows calved 1-2 weeks early during the outbreak and one heifer and one 2nd lactation cow aborted their calves 50 days and 35 days early, respectively. Two other heifers aborted their calves around 60 days gestation. There was an increase in retained placenta and metritis rates during and after the pneumonia outbreak with one case of severe pyometra.

Due to the initial high death loss, the producer decided it was necessary to purchase fresh heifers. We agreed that this could only be safely done after the whole herd had a recent intranasal Nasalgen® vaccine. This was achieved by slowly vaccinating groups of healthy animals and was completed by early April with 32 fresh heifers arriving mid- April. All of these purchased fresh heifers had received intranasal Nasalgen® two weeks prior to travel. There was no significant rise in pneumonia cases after the arrival of the fresh heifers, however, within a few weeks Mycoplasma mastitis was diagnosed in 4 animals for the first time ever in this herd. These cows were culled immediately, and no other cases were detected by aggressive screening.


On this farm, all animals are housed in the same barn except for young calves under 6 months of age which start in hutches as newborn calves then move into a group-pen calf barn.

The vaccine protocol includes a live 10-way viral respiratory and leptospirosis vaccine (Express FP10 ®) in heifers (at 6 months and before breeding) and fresh cows, J-VAC® every 3-4 months in all mature cows and late gestation heifers, Guardian® to all cows and Nasalgen ® to newborn calves. Prior to this pneumonia outbreak there were hardly any cases of pneumonia in mature cows and only occasional cases of pneumonia in the calves.

Mannheimia haemolytica is a commensal bacterium of the upper airways of cattle and other ruminants. It is recognized as an important pathogen in pneumonic pasteurellosis of cattle (shipping fever pneumonia)1, but more recently it has been recognized in surveillance reports as causing pleuropneumonia outbreaks in mature dairy cows2. Our suspected primary risk factors for the cause of the MH2 outbreak include the introduction of new animals into the herd, vaccine status and age of the herd. After closer evaluation of the herd’s records, it was determined that 30 (35%) of the mature animals did not have an up-to-date Express FP10® vaccine. Additionally, a group of 10 fresh heifers arrived at the farm on March 3rd; approximately 1 week before the outbreak was reported to the clinic. Although the actual date of the first sick cow was not recorded, the producer believes initial symptoms started around March 1st, just before the arrival of the new cattle. It is possible that the pneumonia outbreak started as a viral infection which exploded into a bacterial pneumonia with the introduction of the new animals.

Initially the producer was monitoring for new clinical cases based on milk production, however, we determined that taking daily rectal temperatures allowed for earlier detection of affected animals before onset of other clinical signs, and these animals responded better to treatment. Having a rumination or temperature monitoring system on farm could have been extremely useful and significantly reduced time spent taking rectal temperatures. Once we confirmed the pathogen was MH2, we modified the treatment protocol and the producer reported a better response to flunixin (Banamine®) intravenously as opposed to ketoprofen intramuscularly as measured by return to milk production. Once the primary outbreak was over, we started using more TMS to reduce costs which seemed just as effective as ceftiofur treatment. Youngstock did not respond as quickly to florfenicol compared to long-acting oxytetracycline therapy.

The overall financial loss due to the MH2 outbreak was quite large; in March and April, income from milk production was down by 70%, and 24% of total animal value was lost. Veterinary costs in March were 10x greater than normal and 2x greater in April. There was also the additional cost from purchasing the 32 replacement heifers. After approximately 3 months, it was safe to say the herd had returned to its normal daily schedule. The plan going forward is to close the herd and avoid purchasing any more animals and a new vaccine protocol that includes bacterial pneumonia protection has been established.

Thank you to Raymond Reynen, Cynthia Miltenburg, and other veterinarians/local veterinary clinics who provided advice and support.

New Salmonella Dublin Diagnostics Guide for Veterinarians

Check out our new guide: Monitoring and Diagnostics for Salmonella Dublin. The guide helps practitioners to select and interpret S. Dublin diagnostic tests.

This guide was prepared by Cynthia Miltenburg, Durda Slavic, Andrew Brooks and David Renaud with support from the OAHN bovine network and the Salmonella Dublin working group.

The guide covers:

  1. Diagnostic Testing on Postmortem Tissues
  2. Antemortem Sampling
  3. Herd Monitoring and Carrier Identification

The guide is available at:

Salmonella Dublin Diagnostics Guide

Other important S. Dublin resources:

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