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BC HOLSTEIN NEWS a FALL 2020 BC HOLSTEIN NEWS a FALL 2020
BC DAIRY
A Future with
Diseases Affffectiting Dairy Herds Q&A with the Experts
By Aimee Laity, BCDA
In recent months, a number of producers have reached out to BCDA about diseases affecting dairy herds. BC Dairy recently had the opportunity to interview two local veterinarians, who shared their perspectives on Salmonella dublin and Mycoplasma bovis.
        Dr. John Dick
Dr. Dave Dykshorn
GREENBELT VETERINARY SERVICES
ABBOTSFORD VETERINARY CLINIC
Salmonella dublin
Q: I understand there are several different strains of Salmonella. Can you tell us about Salmonella dublin?
A: Most types of Salmonella infections produce diarrhea with fever and depression. Salmonella enterica Serotype dublin infection is different and often presents as pneumonia. S. dublin is also unusual because it is a cattle-adapted strain and a proportion of the animals that survive infection will become carriers for life. These carrier animals intermittently shed, making it very difficult to eradicate S. dublin once it is present on the farm.
Q: How can producers recognize the signs?
A: S. dublin is challenging because carrier animals may appear healthy and clinical disease can present in different ways. Infected young calves are more likely to show symptoms while older cows may show no signs of disease. In two of our herds, it was first identified in weaned calves in group pens after movement from hutches. Calves had high fevers, respiratory signs, and diarrhea but did not respond well to treatment. It can also cause severe pneumonia and sudden death in young calves on milk. Veterinary colleagues in other provinces have had outbreaks of sudden deaths in lactating cows due to S. dublin.
Q: How does it spread?
A: Spread is primarily by oral ingestion of the bacteria from a contaminated environment or feedstuff. Infected animals will shed bacteria in all bodily secretions. Calves are sensitive to infection and are more likely to become chronic carriers.
Q: Can Salmonella dublin be transmitted to calves via the milk supply?
A: Yes. Unpasteurized colostrum and whole milk fed to calves are sources of infection. If milk cannot be pasteurized, milk replacer is a good option. Cleaning and disinfection of all calf feeding equipment is very important.
Q: How do you recommend treating Salmonella dublin? Any advice for producers who identify an infection?
A: This is one of the diseases we want to try to prevent rather than treat. S. dublin is multi drug resistant and difficult to cure. Culling is often the only option for animals that survive infection. Antibiotic treatment makes it more likely cattle will become chronic carriers even if they seem to respond to treatment. Animals that are younger when infected are also more likely to become chronic carriers.
Producers that identify an infection in their herd should consult with their veterinarian. Increased biosecurity to prevent spread is very important. A blood test for S. dublin antibodies can be used to determine the prevalence of exposure and identify chronic carriers. Unfortunately, confirming chronic carriers requires multiple blood samples and can be cost prohibitive.
Q: What are the risk factors involved?
A: The most likely way to bring S. dublin
into your herd is through purchased animals. Maintain a closed herd if possible. If you need to purchase animals, consider antibody testing of the bulk tank or individual animals in the source herd.
Biosecurity and sanitation are important in keeping this disease out of your farm and reducing its spread once it is present. Exceptional calf management also reduces risk. Remove calves from the maternity pen as soon as possible, feed pasteurized colostrum/milk or milk replacer, and sanitize all calf feeding equipment.
Q: Any final pieces of advice for dairy farmers when it comes to Salmonella dublin?
A: Get your veterinarian to investigate if you have any unusual sickness or death loss, especially in calves. Routine post-mortem examination of pneumonia and diarrhea cases are useful for diagnosis.
Remember, Salmonella is zoonotic and has the potential to infect people causing illness and death. Consumption of raw milk is high- risk, especially for people with weakened immune systems.
Mycoplasma bovis
Q: What is Mycoplasma bovis?
A: Mycoplasma bovis is a unique bug that is found in cattle all over the world and can cause a variety of bacterial diseases in herds, including mastitis, pneumonia, ear infections in calves, swollen joints, lameness, and even reproductive disorders or abortions. It belongs to the mollicute family, which is important to note as these bacteria lack a cell wall, making them naturally resistant to a number of antibiotics. The good news is that it is not zoonotic, so humans cannot contract any M. bovis diseases by working with infected cattle or consuming their milk or meat.
Q: How can producers recognize the signs in their herd?
A: Keep an eye out for mastitis, pneumonia, and/or swollen joint arthritis. M. bovis infections can be identified as a cause in cases of chronic, unresponsive mastitis, severely swollen joints, bacterial pneumonia in calves, and calf head tilts (middle ear infection). It’s important to work with your vet to confirm an M. bovis infection via targeted diagnostics.
M. bovis is most commonly spread through close aerosol and nose-to-nose contact between infected animals and via contaminated equipment, usually in the parlour as it can behave like a contagious mastitis pathogen. It is also spread from cow to calf via dam-infected milk. Once M. bovis is seeded, it can be highly contagious from cow to cow. The danger is that the bug can infect an animal and it doesn’t show any signs. “Asymptomatic carriers” and shedders of M. bovis are the primary means to which a herd is infected.
Q: Can Mycoplasma bovis be transmitted to calves via the milk supply?
A: Transmission of M. bovis through the untreated milk of an infected cow to calves is usually how M. bovis is initially spread. An infected cow’s milk infects the calf and that calf will either fight off the disease, break with disease (like pneumonia or ear infection or arthritis), or become an asymptomatic
carrier that goes on to infect its herd mates. It is highly likely that once this animal is infected, it will be infected for life, usually shedding M. bovis after a stressful event, like a primary viral pneumonia infection or weaning stress, for example.
Q: How do you recommend treating Mycoplasma bovis?
A: The key for treating Mycoplasma infections is early detection and treatment with effective antibiotics and pain medication/anti-inflammatories. Talk to your vet about identifying the signs. In the case of Mycoplasma mastitis, consider culling confirmed positive cows as they are untreatable and pose a disease spread risk. Include positive animals in your biosecurity plan to quarantine, cull, or dispose milk from them.
Q: Any idea of how prevalent Mycoplasma bovis is in BC?
A: There is not much available for M. bovis prevalence data, but it would be prudent to surmise that M. bovis is relatively common in BC at a herd level. Most herds would not have an endemic/ongoing M. bovis problem; however, they may have or will experience cases of M. bovis, manifesting primarily as pneumonia. The fact that M. bovis is not easy to diagnose and it’s not easy to treat makes it hard to track!
Q: What should producers do to prevent Mycoplasma bovis from infecting their herd?
A: One of the best things you can do is to pasteurize milk fed to calves. Proper pasteurization will kill any M. bovis in the milk and maintain nutritional integrity. If you have a known M. bovis cow in your herd, ensure that their milk or colostrum never gets fed to calves.
Remember that M. bovis infections are often secondary to something else, like an external stress or a different primary pathogen. Ensuring that your entire herd is on a BRD (bovine respiratory disease, or pneumonia) vaccination program will help prevent most M. bovis pneumonia infections and reduce the prevalence of asymptomatic carriers in the herd.
        




















































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