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 Highlights

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

  • Cases of pneumonia caused by several bacteria including M. hemolytica, P. multocida, Bibersteinia trehalosi, and M. bovis
  • Enteritis caused by bovine coronavirus
  • Cases of neurologic disease attributed to polioencephalomalacia, and listeriosis
  • A case of clostridial myositis (blackleg)

Older Calves Highlights(2 mo. to 2 years)

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

  • Pneumonia (M. hemolytica, Pasteurella, M. bovis, mycotic, idiopathic interstitial pneumonia)
  • Enteritis/colitis (coccidia, cryptosporidiosis)
  • Septicemia
  • Clostridial myositis (blackleg)

Young Calves Highlights (< 2 months of age)

There were 41 submissions (dairy n=18, beef n=22, not specified=2).

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

Abortion/Stillbirth/Premature Birth

There were 22 submissions for abortion investigations (dairy n=21, beef n=1). Presumptive or definitive diagnosis was reached in 15 cases

  • Bacterial (isolates included Bacillus licheniformis, Streptococcus pluranimalium, Campylobacter fetus subsp. fetus)
  • BoHV-1 (Infectious Bovine Rhinotracheitis)
  • Neospora
  • Ureaplasma
  • Leptospirosis
  • Malformation


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.

A Mannheimia hemolytica outbreak in a lactating dairy herd

On Friday March 11th 2022, an 85-head freestall dairy client contacted their veterinarian to report a suspected viral pneumonia outbreak in his herd. He reported a decrease in feed intake and milk production with several coughing adult cows.

Initially the sick animals were only treated with anti-inflammatories. A treatment plan was recommended to vaccinate all animals with an intranasal respiratory vaccine and treat sick animals with a first-line antibiotic. Early clinical signs of fever, dullness, and coughing progressed rapidly to bloody nasal discharge, respiratory distress and death. By Sunday March 13th, the producer had 6 dead cows. Nasal swab samples were collected from affected live animals and lung tissue samples from postmortems and sent to the Animal Health Laboratory (AHL).

The recommendation to vaccinate the herd was initiated on March 13/14 and antibiotic treatment for affected animals was started on March 14/15. At this time, it was suspected that most of the lactating herd was already sick or exposed. 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).

By March 16th, 22 cows had died, and 28 mature cows were being treated with a treatment protocol of 5 days of antibiotics and 3 days of anti-inflammatories. After the sudden death of a mature heifer on March 16, it was noted that most of the youngstock had increased temperatures and occasional animals were dull and coughing. All young calves and heifers received a long-acting antibiotic treatment that day

On March 18, lab results confirmed Mannheimia haemolytica type 2 cultured from both the nasal swabs and lung tissue. All viral testing from the nasal swabs and lung tissue was negative.

Outbreak Aftermath

In total, 43/75 remaining live milking and dry cows became sick and received treatment. Approximately 50% of these mature animals required a second round of treatment and 7 animals required a third. 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. 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 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, 4 heifer calves born to dams that had calved and developed MH2 pneumonia became ill with severe scours. Due to concern for poor colostrum quality, all subsequent calves born were given powdered colostrum with an oral antibody product and an intranasal 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 there were 2 late-stage abortions. Two other heifers aborted around 60 days gestation. There was an increase in retained placenta and metritis during and after the outbreak.

Due to the initial high death loss, the producer needed to purchase replacements. Prior to the arrival of 32 fresh vaccinated heifers, the whole herd had received a recent intranasal vaccine. There was no significant rise in pneumonia cases after the arrival of the 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.


Mannheimia haemolytica is a normal bacterial inhabitant of the upper airways of cattle and other ruminants. It is recognized as an important pathogen in shipping fever pneumonia, but more recently has been reported as causing pneumonia outbreaks in mature dairy cows.

Prior to this pneumonia outbreak, the herd was following an established vaccine protocol and there were hardly any cases of pneumonia in mature cows and only occasional cases of pneumonia in the calves.

The suspected risk factors for the MH2 outbreak include the introduction of new animals into the herd, vaccine status and age of the herd. Upon evaluation of the herd’s records, it was determined that 30 (35%) of the mature animals did not have an up-to-date vaccine status. 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. 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 cases based on milk production, however taking daily rectal temperatures allowed for earlier detection and these animals responded better to treatment. Once MH2 was confirmed, the treatment protocol was modified and the producer reported a better response as measured by return to milk production. The overall financial loss due to the MH2 outbreak was 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 of purchasing 32 replacement heifers.

After approximately 3 months, 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.

This case emphasizes the potential severity of Mannhemia hemolytica outbreaks in mature cattle and how early intervention, diagnostic testing, and a veterinary instituted treatment protocol can improve outcomes.

The OAHN bovine network gratefully acknowledges the time our member veterinarian spent summarizing this case for the benefit of all.

Reminder Salmonella Dublin Resources

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