Calf Housing and Bovine Respiratory Disease

Dr Natalie Meades: IBERS, KEHub, Aberystwyth University. 

January 2024

• 
  Bovine respiratory disease (BRD) is one of the main causes of calf mortality in the UK and can be costly to producers through loss of animals, treatment costs and poor animal performance in later life. 
• The causes of BRD are multifactorial and include factors associated with the calf itself, the environment and pathogens. 
• It is important that calf housing is sufficient to support animal health and welfare and encourage growth and performance. Inadequate housing in terms of poor air quality and inadequate temperatures can contribute to the development of BRD.
• When evaluating the suitability of calf housing environments consideration should be taken with regards to the ventilation, temperature, humidity and air speed within buildings. 

Introduction

Bovine respiratory disease (BVD) otherwise known as pneumonia is a disease of the respiratory tract that involves the inflammation of tissues associated with the lungs and airways. This disease is particularly common in young calves and has been demonstrated to be one of the primary causes of calf mortality in the UK. Moreover, it is estimated to cost the UK agricultural industry £80 million pounds per year and affect over 1.9 million animals per year.

Calves affected by BRD often display poor growth rates and in the case of beef calves, longer finishing times. Moreover, calves affected by BRD often display poor performance in later life, examples of which include poor carcass qualities, delayed age to first calving and not surviving through to the second lactation  in milking herds. As such, BRD can lead to reduced farm efficiency and economic loss through loss of production. Likewise, the treatment for BRD often involves the use of antibiotics (depending on the pathogen) which are costly. Furthermore, high usage and overuse of antibiotics is greatly concerning for the industry and wider regarding antimicrobial resistance, food safety and consumer acceptability of produce. Therefore, it is essential that cases of BRD are reduced on farm for animal health and welfare, farm efficiency, economics and food safety.    

What causes Bovine Respiratory Disease

The cause of BRD is multifactorial and consists of a range of pathogenic microorganisms and a range of factors associated with the calf itself and its environment. Examples of these can be found in Table 1. There are several pathogens that can contribute to causing BRD, therefore it is important for farmers to work alongside their veterinarian to identify which pathogens are present on farm for targeted and effective treatment. Physiological state can also influence a calf’s susceptibility to BRD, where calves that are stressed or immunocompromised are most susceptible. As such, calves that are young, recently weaned or those that have been introduced to new environments or management systems can be highly susceptible. Finally, the environment in which a calf lives in can also contribute to the development of BRD where housing that has poor air quality and/ or inadequate temperatures can increase the risk of calves developing BRD.  

Calf Housing

It is important that calf housing environments support animal health and welfare and encourage growth and development. The suitability of calf housing can be evaluated by looking at the housing structure and management within it. Housing structure is important as it provides calves with shelter from the elements and comfort. Moreover, the structure of housing environments can influence air quality, that is the level of aerosols within the air which are breathed in. Examples of aerosols include, noxious gasses (ammonia, hydrogen sulphide, carbon dioxide, carbon monoxide and methane), dust and microorganisms (pathogenic and non-pathogenic). As such, the repeated inhalation of air of a low quality can contribute to respiratory irritation and therefore the likelihood of developing BRD. Moreover, the repeated inhalation of air of a poor quality can be potentially damaging to human respiratory health.     

In reality there is no one best housing structure, with each type having its advantages and disadvantages in comparison to one another. A study conducted in the UK compared housing dairy calves from birth to weaning in hutches, polytunnels and sheds. In this study, it was found that calves housed in hutches and polytunnels were more susceptible to conditions that may cause the onset of heat and cold stress and calves that were housed in sheds were more exposed to greater levels of particulates and airborne bacteria. Likewise, a study conducted in America demonstrated calves housed in polyethylene hutches to have greater internal temperatures and higher humidities within the hutches compared with the external air and to a calf housing environment within a shed.

When evaluating the suitability of housing structures, the following factors should be taken into consideration;

• Ventilation
• Air speed
• Temperature
• Humidity

Ventilation

Ventilation within housing environments is an important factor to take into consideration with regards to air quality and temperature. It is estimated that a shed with sufficient ventilation will have at least four air changes per hour, however this may need increasing during warmer weather. Good ventilation within housing environments is essential where it can help to dilute the concentration of airborne pathogens, endotoxin levels, noxious gasses and dust particles within the air which all contribute to poor air quality.  Moreover, sufficient ventilation within housing environments can help create and maintain suitable temperatures and humidities and remove drafts, water vapour and stagnant air. However, care is needed so that ventilation does not create any unwanted drafts, especially at calf height, which could lead to cold air causing calves to become chilled and have compromised mucociliary clearance. As such, the air speed within sheds is an important factor to take into consideration, where according to the AHDB an air speed of 0.25 m/ second is thought to be ideal at calf height.

Within livestock sheds in the UK, ventilation is often by non-mechanical means and primarily based on the stack effect, where the heat generated from livestock is thought to be sufficient to move air within sheds (Figure. 1). However, some argue that this is not the case in calf sheds due to the inability of calves to physically produce enough heat to have this effect, especially in large sheds. It is therefore suggested that external air (wind), is the main driver of air movement within sheds. As such there may be times throughout the day and night where ventilation is inadequate. Therefore, it is important to consider the structure of calf housing environments and how buildings are ventilated. With regards to sheds it is recommended that the number of inlets and outlets on buildings are balanced so that fresh air can enter from whichever the wind direction is and be evenly distributed around the building. Likewise, consideration is needed for any structures on farm that are close to housing environments such as trees, other farm buildings or silage pits that may obstruct air flow to the shed.

There are various visual and physical methods that can be carried out on farm to determine if a shed has adequate ventilation and air flow. Firstly, sheds can be inspected for cobwebs, where the presence of cobwebs can indicate poor ventilation and air flow. Likewise, the presence of condensation and the smell of ammonia can also indicate poor ventilation and damp. Moreover, smoke bombs can be set off in sheds and the direction of the smoke and time it takes for the smoke to fully clear recorded. These are all relatively simple and cheap techniques that can be carried out on farm. Other techniques such as measuring the air speed at inlets using anemometers and measuring the concentrations of noxious gasses can also be measured, however this requires the use of specialist equipment which can be costly.

Temperature

The temperature within housing environments is another important factor to take into consideration, where prolonged exposure to the cold can contribute towards the development of BRD through thermic stress. Calves like any homeothermic mammal are able to regulate their core body temperature through homeostatic mechanisms (metabolic heat and with heat exchange with environment). To put this into perspective, the lower critical temperature in which additional energy is required to generate heat is thought to be 10-15 ^oC for calves aged 0–2 weeks and 6-10 ^oC for ages thereafter (air speed, ventilation and draught dependant). As such, there may be periods in the winter and overnight where temperatures are low and calves utilise energy and reserves to keep warm. This can be particularly problematic if energy is repeatedly prioritised for keeping warm over other important physiological processes such as the immune system and growth. Moreover, when temperatures are extreme thermoregulatory mechanisms are likely to be ineffective at keeping calves warm and can lead to thermic stress.

There are many ways in which calves can be kept warm. Examples of which include, the use of breathable calf jackets within the first 30 days of life and increasing the plane of nutrition to provide more energy within the diet. Likewise, the choice of bedding within housing can be important, where certain types of bedding can help to reduce heat loss via conduction and provide insulation when calves are lying down. Deep straw bedding has been demonstrated to be a good choice of bedding where it is often associated with high nesting scores, which represents the degree at which the calf is able to cover itself in bedding to keep warm.

Conversely, it is equally important that calves are not too hot which may lead to heat stress. Heat stress can be problematic especially in the summer months where it can result in, reduced average daily live weight gains, reduced feed intake, dehydration and in extreme cases death. To accommodate buildings can be modified to increase ventilation and some farms opt to install fans to drive air movement. A study in North America demonstrated calves housed in sheds over the summer months with increased ventilation provided by a fan had greater average daily live weight gains by 23% and greater feed efficiencies by 20% in comparison to calves that did not have access to fans within their housing environments. Likewise, it has been suggested that elevating calf hutches can help to increase the air flow and reduce internal temperatures within hutches as well as improve the removal of gases such as carbon dioxide thus improving air quality.

Humidity

Humidity is another important factor to take into consideration within calf housing environments as it can influence how damp the environment is. Where damp, humid environments are conducive for the growth and activity of certain pathogenic microorganisms. It is suggested that the humidity in which airborne BRD pathogens have the least survivability is around 40-60%. Furthermore, the humidity can have an influence on the temperature within housing environments. Therefore, it is important that sheds are not too high in humidity and are much below 80%.

To ensure calf housing units operate at suitable humidities the ventilation of buildings can be investigated as described previously. Where good ventilation will help to remove any moisture within the air and supply the building with a regular supply of fresh air. Likewise, it is important that bedding is kept clean and dry where the accumulation of faeces and urine within bedding can add moisture to the air and contribute to increased humidity. Likewise, the humidity within a building can also be affected by spilt liquids such as milk and water, therefore it is essential that buildings have good drainage and any washing equipment is kept outside of buildings. 

Summary

Bovine respiratory disease (pneumonia) is one of the main causes of mortality and poor performance in calves in the UK. As such, BRD can negatively affect animal health and welfare, farm efficiency and economics. Calves are particularly susceptible to developing BRD due to having underdeveloped immune systems and from exposure to environmental stress. The causes of BRD are multifactorial and involve factors associated with the calf itself, pathogens and the environment.

It is important that calf housing is adequate to promote good health and welfare and to encourage growth and performance. When rearing calves on farm it is important to consider the suitability of housing environments, where housing that has poor air quality and inadequate temperatures can contribute towards the development of BRD. Therefore, when assessing the suitability of calf housing the ventilation, air speed, temperature and humidity should be evaluated.