18 Nov 2019
Tony Andrews
Job Title
Figure 1. Calf hutches facing south in a sheltered old cattle courtyard.
Bovine respiratory disease (BRD) is a fact of life in the UK, as well as North America and other parts of Europe.
It affects either housed calves kept for dairy or beef production – usually in the first few months of life – or suckler calves, again, usually while housed.
In both cases, the problem will often follow stress caused from management procedures, such as weaning, a change of environment or feeding, regrouping or undertaking routine tasks – for example, castration or disbudding. Other factors can include weather changes – particularly when calves are housed. Marked diurnal variation in temperature and, often more importantly, humidity (high, increasing or low) are involved. Previous illness or concurrent disease can also exacerbate the problem.
However, many other factors can be involved, and when a thorough investigation of an individual BRD outbreak is made, these may become apparent.
In some other parts of the world, BRD is uncommon, although many of the BRD pathogens are still present. In New Zealand, it is a minor calf problem, and only occasionally encountered, while here it is one of the most common calf ailments. Similarly, BRD is not a major factor in Australian calf rearing.
Why the difference? Much is probably due to calf management and the environment in those countries. Most dairy herd calves are born in the spring there, and usually weaned at a day old. They are initially kept in groups in multipurpose barns with high roofs and, once strong enough, the calves go outside to pasture in mobs of about 30 to 50, where they are usually fed via a “calfeteria” – a milk container with many teats that is often mounted on, and transported by, a tractor to the field.
Natural or rudimentary shelter is provided and, depending on grass availability, some forage and limited cereal or concentrate mixture is usually offered.
Therefore, the Kiwi system for dairy calves is, in many ways, more natural than that used in the UK, and, with the exception of the quick weaning, is similar in many ways to beef suckler production. The calves go outside while any passively acquired immunity from colostrum is still high, and then are in an environment less conducive to micro-organisms or the buildup of pathogen load.
In the UK, respiratory problems tend to be few in suckler calves born outside in the spring and any such troubles usually arise at housing or following weaning. Therefore, perhaps using these observations as a partial basis for a template, any health plan to deal with respiratory disease should aim at keeping management as near natural as possible and make stresses minimal (Panel 1).
Where stresses are unavoidable, they should be anticipated and, where possible, mitigated against to reduce their effect. In case you are wondering, the author is not advocating the New Zealand system for our dairy-bred calves. The system depends on having a predictable and suitably favourable climate and environment, which is not the case in the UK’s spring.
The author has heard anecdotally of people from New Zealand trying to turn out and feed calves at pasture in Britain, but with limited success, and often resulting in illness and death. However, the system’s underlying principles should be borne in mind.
Generalising, a strong, healthy calf is more likely to have ingested more colostrum than a smaller, weaker animal. However, this is not necessarily the case, because so many factors affect colostrum quality, intake and absorption.
When blood sampling calves in BRD outbreaks, it is often noticeable they have low globulin levels. It has been shown calves with low Ig levels (IgG1, IgG2 and IgA) at two or three weeks of age are more susceptible to pneumonia when two or three months old. The only way to be certain of a calf’s immune status is to undertake a suitable direct or, more likely, indirect test.
Where calvings are being concentrated in a short period, it is often advisable to test several calves early on in the calving period, and ensuring the testing is within the appropriate time period. This can give an early indication as to whether all is well or any problems could possibly arise.
If the results show some calves with low circulating Ig levels then the reasons for this can be investigated. In most instances, it may involve allocating someone to specifically oversee calvings, and also the same, or another, person to ensure good colostrum uptake. In such circumstances, once the new programme is introduced, it is probably advisable to undertake further sampling to check the measures are working.
Several studies have shown that if calves develop calf enteric infections and then contract respiratory disease, they tend to suffer a greater reduction in their subsequent growth rates than would be the case on an additive basis. Therefore, reduction in enteritis in a herd should reduce the impact of respiratory disease, and it could be argued vaccination of dams for the main enteric pathogens is likely to assist in calf pneumonia control.
Anyone with experience of respiratory problems in young calves, and who has taken properly timed, paired blood samples, will realise, in many cases, antibodies to some respiratory pathogens are not rising – indicating their absence as a probable cause of the pneumonia outbreak.
However, other pathogen antibody titres often show a reduction, obviously suggesting they were not involved in the disease and also indicating they were present in these young calves through passive immunity transfer from the colostrum, with the level waning later.
Such observations make it appear logical that, just as with calf scours, vaccinating dams of calves in herds with early respiratory disease outbreaks should be considered. If done at the correct time for the vaccination programme to create a high immune level and with sufficient time to allow antibodies to enter the colostrum, this should mean higher colostral antibody levels for increasing passive protection of the calf.
An initial study by Makoschey et al (2008) showed passive protection to the respiratory disease pathogens bovine respiratory syncytial virus (bRSV) and parainfluenza virus 3 could occur, and suggested this might also be expected to be seen for other pathogens.
Another paper by Makoschey et al (2012) has shown the application of this process. Therefore, cows were vaccinated with iron-regulated proteins of Mannheimia haemolytica. Following the vaccination and calving, the resultant enhanced immune colostrum or a freeze-dried colostrum supplement for the control calves was used in 24 colostrum-deprived calves.
When aged about three weeks old, all the animals were experimentally challenged with M haemolytica. Both the vaccinated colostrum and control groups developed respiratory disease signs and lung lesions. However, the survival rate was considerably higher and M haemolytica count was 10 times lower in the calves receiving the colostrum from vaccinated cows. This showed the calves receiving the vaccinated cow colostrum were partly protected against a severe M haemolytica challenge.
Potential benefit can, therefore, be seen in using M haemolytica vaccination in the dams of young calves where outbreaks of disease occur before the time when calf vaccination would be effective. However, much more work needs to be done with this and other pathogens before the findings are conclusive.
A news article in Veterinary Times by Holly Kernot (2017) described collaborative work at The Pirbright Institute and other laboratories concerning a perfusion-stabilised bRSV vaccine. A viral protein (fusion [F] glycoprotein) allows the virus to enter cells and is in two forms – a perfusion form (pre-F) produces good immunity, but is unstable, and a post-fusion (post-F) form, which produces a weaker antibody response that is more stable.
Zhang et al (2017) have been able to produce, by genetic engineering, a stable protective D52 protein that produces a good immune response in calves. It has been suggested this antigen technology could be used in vaccines to inoculate pregnant cattle.
The use of this technique means colostrum management must be aimed at ensuring high antibody levels to specific respiratory pathogens enter the body. In such cases, the aim must be to obtain high colostrum uptake in the first six to eight hours after birth and continue this for the following 30 to 40 hours to ensure as much of the immunity as possible is absorbed.
Once gut closure is complete, the other benefits of colostrum still remain, but any circulating antibody levels to respiratory pathogens will have peaked. The more antibody to enter the body the longer the passive protection will remain, ensuring these young calves do not develop illness or, if they do, that it is milder than would have been the case without vaccination.
Once the calves are older, they can again be vaccinated against specific respiratory pathogens, where appropriate. In all cases of respiratory disease it is unfair to expect any vaccine to work in calves, unless other environmental and management issues are also addressed.
In addition, it is a good policy to check calves at periodic intervals to see the colostrum intake and gamma globulin uptake is satisfactory. This can be done with any standard test, such as the zinc sulphate turbidity test, or by using a refractometer, and can indicate a change of management or circumstances before any disease outbreaks occur.
Calves should receive colostrum as soon as possible after birth. Ideally, while it should be done by allowing natural sucking, it is often far too hit and miss on many farms. This is best overcome by feeding colostrum, and again, ideally, via a teat. However, when this is not practical, the use of a stomach tube ensures colostrum is provided.
This process should be done as cleanly as possible. Ideally, feeding should be done in as stress-free an environment as possible, and with the dam or another cow present. Differences in opinion exist as to how much should be fed. In the US, the amount given is often about one to 1.33 gallons (4.5L to 6L) in one feed.
However, the author would personally prefer two feeds – each of about 2L, with one soon after birth and the other towards six hours. This smaller volume is more similar to the calf’s abomasal capacity. In old money, the adage six pints in six hours was always useful to remember.
As already indicated, housing can play a major role in determining the presence and severity of any respiratory disease infections. Usually, calves are not housed in purpose-built buildings, but often in multi-purpose barns that are far from suitable for the purpose.
While they may be satisfactory for older cattle, they are often far from suitable for calves. Often the problems are the result of moisture, lack of fresh air and low air speed (Robertson, 2015). About half of all naturally ventilated cattle buildings, both old and new, are not fit for purpose.
It is beyond the scope of this article to go into detail on buildings, although the subject should be addressed in any health plan. When pneumonia outbreaks occur, the building environment should always be taken into consideration. Many problems are the result of alterations in the environmental conditions, and they can be the result of poor ventilation and a lack of suitable drainage.
Bearing in mind the theory conditions for calves should be kept as natural as possible, the use of calf hutches is a very useful method of providing a good environment. Calf hutches, as used in North America, were introduced to the UK and other European countries in the late 1980s and early 1990s.
In the UK, they were initially sold to top-end dairy breeders. Usually about 250 to 300 were sold annually, but in the early 1990s numbers sold were very low. However, following a different company taking over distribution, calf hutches have been increasingly used on many dairy farms. Currently, the author believes about 2,000 are sold annually and about 98% go to dairy farmers. Various types of hutches are sold by different manufacturers and distributors, and probably more than 50,000 are in use in the UK.
The uptake has increased because the hutches can greatly assist in controlling disease problems. They reduce the potential for calves to succumb to the main diseases of an infectious nature, such as calf enteritis, respiratory diseases, navel sucking and some cases of septicaemia. They can be particularly helpful in controlling calf respiratory disease.
Calf hutches have the advantage their use is usually more natural and welfare-friendly than housing calves indoors. They allow each animal to have its own microclimate, with the ability of providing more space than is usually available indoors, as they consist of a shelter and outside penned area.
They can provide a suitable environment for the calf as well, as keeping each animal individually or in twos or small groups reduces the chance of disease spread. They also have the advantage they can be placed in different parts of the farm. While the author has seen some hutches used inside buildings, this rather defeats the object – and in most situations, they are best kept outside.
Hutches do require sufficient bedding to allow the calf – especially when young – to insulate itself from the ground and also ensure it can snuggle down away from draughts. Extra feeding can offset the problem of increased energy use in cold weather.
Some thought needs to be given to where hutches are situated. The hutches should usually be sited to face south and away from any prevailing wind. Their relationship with their surroundings needs to be considered. Therefore, in Figures 1 and 2 – both photos taken on the same farm – some hutches were placed in an open, but sheltered, farm yard and others were in a area where the wind may potentially funnel to produce draughts or assist in driving rain through the hutch doorways.
As far as the author can see, one of a hutch’s main drawbacks is in some designs it lacks easy access to the calf when inside the hutch. Very occasionally, in gales and heavy rain, water may enter the hutch, but good stockmanship will overcome this and usually the calf will be able to find a sheltered area.
The Welfare of Farmed Animals (England) Regulations 2007 Schedule 6 deals with calves and their requirements. However, although hutches have been around for about 30 years, the schedule makes very little reference to them. Most of the text is focused on indoor calf rearing, and their requirements are extrapolated to calves in an outdoor environment provided by hutches.
Exposure to the inclement conditions of winter can lead to hypothermia. This is well recognised in lambs, due to exposure or starvation, but is less commonly seen in calves – partly because they are usually housed. However, the young calf has a very large surface area compared with its weight and volume, so it has the potential to become chilled.
In New Zealand, where calves go to pasture at an early age, it is not unusual for the small ones in a batch or those born early in the season to wear calf jackets or calf coats (Figure 3). These can also have advantages in the UK, when outside calf hutches are used during cold periods. The Agriculture and Horticulture Development Board (2018) has produced practical advice on their use.
Limited, independent advice is available on their benefits, but provided they are impervious and have some insulation, these coats would appear to be of use for suitable calves. They are reusable, but should always be cleaned and disinfected before placing on another calf. This should be routine anyway, but still needs to be stated as these jackets will mainly be used on weaker or vulnerable calves.
The author has often made his own calf jackets out of 20kg or 25kg feed bags, held in place on the calf with the ubiquitous baler twine, and then placing dry straw between the home-made jacket and the calf.
A poor, moist environment allows micro-organisms to survive longer and also spread further when breathed or coughed out. However, much respiratory disease spread is by contact. Many of the organisms – especially bacteria – are carried by the calf and only result in illness if and when the animal encounters adverse conditions or situations. Therefore, if an ill animal is identified early and immediately removed, the infection is less likely to spread.
Good stockmanship is the key, but is often lacking. Although early treatment should be the mantra, it has been shown identification of illness by the stockperson is often slow. However, this can be partly overcome by ensuring very regular inspections of the calves. A simple measure, such as a cough count, can also assist.
A device with some promise is ear tags, which light up when the calf exhibits a high temperature for a period. The designs have been altered to make them more robust. The trigger temperature needs to be adjusted to the specific farm to ensure the tags are not triggered in normal healthy individuals.
If they are altered to the particular farm conditions and the farmer develops confidence in their use, they can become a useful tool. They can provide 6 to 12 hours’ warning before other obvious respiratory signs develop. The author’s own experience with them is early removal, and treatment of the identified calf has probably prevented potential respiratory outbreaks occurring and stopped the widespread use of antibiotics in the group.
It is always a good policy in calf respiratory disease to treat animals as soon as signs begin. If this is done, the damage to the respiratory system is minimised. Additionally, the affected animal should be isolated, therefore preventing spread through animal-to-animal contact.
Removal of any source of infection is likely to reduce the need for therapy or curative treatment of a group, and, more importantly, often prevents the need for metaphylaxis or controlled treatment. This can be facilitated by having a separated hospital pen.
If reinstating the animal to the group is considered a possible problem, then one or two others can accompany the ill one. The other reason for isolation is the calf can be more effectively monitored, and its eating and drinking can be satisfactorily assessed.
Ideally, where calf accommodation does not involve outdoor hutches, an all-in, all-out system should be used. While this is usually possible with bought-in calves or a batch-calving system, it is not possible where large calving is spread or all-year-round calving takes place. In these circumstances, as well as for all calves housed in buildings, the ideal number of calves in any one air space is 30 or less.
An air space means a wall extending from floor to roof, so this is not easy to achieve. The drainage should also be separate from other groups. Such systems do assist in preventing the spread of disease and can soon pay for themselves. A footbath should be sited outside each separate housing. This should always be kept clean and contain a suitable disinfectant.
While this may have limited effect in disease spread in some instances, it does assist in building up a good cleanliness and hygiene mentality, and may slow down or reduce a disease outbreak. When problems do arise, a change of protective clothing and footwear should be provided.
Following the filling of a space with calves, other separate and hopefully purpose-use spaces should be used. Then, once all 30 calves have left the area, it should be thoroughly cleaned out, all bedding removed and the pens and equipment dismantled, cleaned and ideally left outside. The pens and equipment should only be returned once the building is completely dry.
As already stated, a hospital pen should be provided. Many farmers do not like having one, as on a well-run farm, it should always be empty, and so is seen as a waste of space. However, the empty pen should be considered a source of pride and not a problem.
The pen should be isolated from the other calf pens and all routine feeds, cleaning and other jobs undertaken after dealing with the healthy animals.
If, despite all precautions, a pneumonia outbreak occurs, it is to be hoped some records will have been kept of what happened and not just the legal requirement to record treatments or deaths. Then, after the event, evaluation should be undertaken to determine why the problem occurred, whether correct preventive measures were undertaken, and whether antimicrobial and other treatments were used correctly.
It should be possible to see how, in future, health planning and management could be improved. It is also an ideal moment to try to alter the environment, to prevent the precipitating factors causing the disease reoccurring and to introduce suitable preventive measures, such as vaccination.
Such analyses can help improve the efficiency of calf rearing and reduce antibiotic use in calves for a condition where much tends to be used.
