31 Oct 2016
Paul Wood advises on measures to protect calves from this multifactorial respiratory disease, such as housing assessment, ventilation, diagnostics and vaccination.
Paul Wood
Job Title
Figures 1 and 2. Stocking density plays an important role in disease transmission. Both understocked and overstocked calf sheds can develop problems.
Calf pneumonia is a complex disease that is multifactorial in origin and a common problem in calves worldwide. In the UK, it has been estimated a single case of pneumonia costs a farmer £43.26 per sick dairy calf, with an added cost of £29.58 per calf for the rest of the in-contact group1.
The long-term effects of calf pneumonia in dairy replacements suggest an incidence of pneumonia in the pre-weaning period can lead to a two-week delay in time to first service2. This delay has been estimated to cost the producer £1.65 per day3. An effect on milk production also exists that can show a 2.2% reduction in first lactation milk yield, which, if we consider a heifer may produce 6,000L in her first lactation1,2, equates to 132L of lost milk at a cost of 29.70p per litre4.
By taking this longer-term effect of pneumonia into account, we can correct the actual cost for each case of pneumonia to £105.56. In UK cow-calf units, these costs are £82.10 per affected calf and £74.10 per calf in the in-contact group1. It is important to note these estimated costs do not take into account the extra labour costs calf disease may incur on the producer.
The main factors that cause bovine respiratory disease (BRD) are most often divided into host factors, environmental factors and pathogens:
Housing plays another important role in the spread of disease in young animals5-9. Many different calf-rearing systems are used around the world – each with their own problems. When housing calves, it is advisable to group animals in similar age groups. This reduces the likelihood of older calves with better immunity shedding harmful levels of pathogens to younger animals; calves younger than four weeks of age are the most susceptible to respiratory infections.
Mixing of age groups can also increase stress and competition for food and water, as well as bullying by older animals10. As well as group type, group size (and, as a result, stocking density) is also highly important for the prevention of disease outbreaks5 (Figures 1 and 2).
Highly stocked housing will lead to increased contact between animals, as well as a higher general pathogen load. If housing is not ventilated nor cleaned regularly, higher stocking densities can also predispose to pathogen buildup and increased humidity and ammonia, which has damaging effects on the respiratory system5,11.
It is recommended calves are kept in group sizes of no more than 12 animals, with fewer than 30 individuals sharing the same airspace in the calf shed11. By reducing group size, it also enables better monitoring of individual animals and identification of disease sooner11. Although the aforementioned factors are reduced in low stocking density settings, many calf sheds rely on the stack effect to drive ventilation11.
If an inadequate number of animals are in a shed, they cannot generate enough heat to drive the pathogen-rich air up and out of the building; instead, it cools as it rises then precipitates back on to the livestock below11. This will result in high pathogen buildup, which can lead to an increase incidence of disease11. Reduced ventilation may also allow the buildup of respiratory sensitisers, such as ammonia11.
The key to good housing is providing good ventilation. The aims of ventilation are to:
In the majority of cattle buildings, we rely on the stack effect (Figure 3) to provide the necessary ventilation. It is important to remember wider buildings are harder to ventilate (the stack effect will start to fail if the building is greater than 25m wide – a steeper pitched roof is better).
Existing ventilation can be improved by some of the following steps:
Assessment of ventilation can easily be performed on farms. It is essential sheds being assessed are filled with the normal amount of stock they would be on any given day. Visual clues to poor ventilation include cobwebs (Figure 6) and condensation (tiger striping). The smell of ammonia can also be suggestive of poor ventilation and damp conditions (Figure 7).
The location of the shed, with regards to the prevailing wind, should be assessed; open-fronted sheds should be sheltered from the prevailing wind, whereas it should blow across a pitched roof. Building insulation and roof type should also be considered in an initial assessment.
Smoke bombs can be used to easily track the movement of air flow in a shed. It is best to perform these tests on calm weather days with all doors shut and in a shed stocked normally. An adequately ventilated building should clear of smoke in a few minutes. The path of the smoke is a good way to demonstrate to farmers how airborne pathogens will move within their sheds. If the smoke lingers around the level of the calves, this is what respiratory pathogens will also do.
Once housing and host factors have been investigated, we can also use various diagnostic tests to identify the causal pathogens. Table 2 details the tests available and what they are useful for. It is always worthwhile consulting with your local laboratory to discuss the most appropriate tests and samples. To get the right answer, we need to ask the right question.
Test results should be used in conjunction with the clinical picture, as the majority of respiratory pathogens are commensals of the bovine respiratory tract. The prompt treatment of respiratory disease in calves is essential to minimise the effects of disease. It is essential, where possible, we encourage farmers to do everything they can to prevent disease. Alterations to housing or colostrum procedures may be straightforward steps that can be done and should be included in a herd health plan.
If disease does occur then prompt identification and isolation of sick animals may reduce the chances of in-contact animals becoming infected. Prompt and targeted treatment is also important to stop outbreaks occurring.
Numerous vaccines are available for a range of different respiratory pathogens, so by identifying the common cause on each farm, we can tailor-make a vaccination programme that not only matches the disease profile, but also works for the management system on the farm. Table 3 shows some of the range of respiratory
vaccines available.
In the control of BRD, it is vital vets work closely with their clients to ensure all contributing factors are identified. Together, we can then make a plan to include some (or all) of the points aforementioned to prepare a plan to deal with this costly disease.
