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Respiratory disease is the top cause of mortality in 1 to 5-month-old calves

Following on from the neonatal calf in our previous article where scour was the greatest cause of mortality (read full article here), respiratory infections top the chart when it comes to postmortem diagnoses for calves aged one- to five months (All-Island disease surveillance report, 2022 – see Chart 1).

Respiratory infections more commonly known as pneumonia, made up over one-third of postmortem diagnoses, with gastrointestinal infections ranking second on the list.

Figure 1: Postmortem diagnoses in one- to five-month-old calves

Immediately post-birth, calves require a minimum of 10% of their body weight in colostrum and it is best practice to follow on with transition milk for the first few weeks of life to set the foundations for good health in the baby calf and beyond.

Often mature cows will have been vaccinated against common pneumonia-causing pathogens which are an issue on the farm. These antibodies are passed via the colostrum for protection in the calf until they can build their own immunity. Research has highlighted calves with poor transfer of passive immunity were associated with higher morbidity and mortality during the first 90 days of life (Sutter et al., 2023). Therefore it is essential calves receive colostrum to get the best start in life and to be able to combat infection as best they can.

Pneumonia is a huge issue, estimated to cost the UK cattle industry an estimated £50m a year (AHDB. 2024).

A large fraction of the costs caused by pneumonia aren’t always obvious, such as decreased weight gain and poorer feed conversion efficiency (FCE). The cost per affected animal can range between £30–£80, but can be more like £500 or more if an animal dies as a result (AHDB, 2024).

Calf pneumonia is a very complex disease and can occur due to many reasons.

• High-stress levels – mixing groups, weaning, transportation etc.

• Immune status – inadequate colostrum

• Poor housing facilities/environment – inadequate ventilation, humidity, temperature, draughts etc

• Herd disease issues

Quite often when a calf is diagnosed with bacterial pneumonia a virus may have gone undetected which may have preceded the development of the bacterial infection – there can be a complex bacterial and viral cause which may take longer to treat.

Bacterial Pathogens

The most frequently identified bacterial agents were Pasteurella Multocida (15.8%) followed by Mycoplasma Bovis (13.7%) and Mannheimia Haemolytica (11.5% – see Figure 2). These pathogens can enter when calves are exposed to stressful situations, such as at housing or during transportation. The pathogens take their chance to invade the tissues of an immunocompromised animal.

Viral Pathogens

The most common viral pneumonia-causing pathogens detected in the surveillance report were as follows:

•RSV (Respiratory syncytial virus)

•IBR (Infectious bovine rhinotracheitis)

•PI3 (Parainfluenza – 3)

Clinical signs generally consist of fever, coughing, depression, loss of appetite, inflammation of the mucosae, nasal/ ocular discharge, and conjunctivitis.

Parasitic Pathogens

Dictyocaulus spp. better known as lungworm was the most common cause of parasitic pneumonia (16.7%). This is most typically seen in calves grazing contaminated pasture.  

Figure 2: Relative frequency of the top ten pathogenic agents detected in BRD cases diagnosed on post-mortem examination, (n=545).

Best practice to help tackle pneumonia in growing calves
If a calf that is presenting with any of the following symptoms it’s might be time to get a veterinary opinion as it may well be pneumonia setting in:
• Dull appearance
• Nasal discharge
• Cough
• High temperature
• Reduced appetite
• Increased respiratory rate
• Depressed look and drooped head

Know what you are dealing with

As mentioned above, it is a complex disease so always best to know what pathogen is causing the infection to know how to treat correctly. Nasal swabs and blood tests can be carried out by the local vet to detect cause and treat accordingly.

Many vaccines are on market which can help prevent diseases from occurring alongside proper colostrum and housing management. Once again if you know the specific pathogens causing havoc on your farm you can tailor your vaccine programme much more effectively.

Take home messages

• Always ensure calf receives a minimum of 10% of its bodyweight in good quality colostrum asap post birth.

• Provide adequate housing with good ventilation, no low-down draughts, avoid overcrowding, keep it clean and dry and avoid sharing accommodation with older animals

• Calves thrive on consistency and can’t cope with stress very well – avoid making any more than 1 change per week e.g. dehorning, moving pens, mixing groups, transporting, vaccinating, nutritional change, weaning, etc.

• Stress = increased cortisol levels = reduced production and activity of immune cells = immunocompromised calf = pathogen take their chance to sneak in = sick calf

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