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RESPIRATORY DISEASES OF CALVES LESS THAN ONE MONTH OLDRespiratory diseases are not common in this age of calf and when they do occur, they usually involve the lower respiratory tract. The following specific disorders can be recognised. NEONATAL ACUTE RESPIRATORY DISTRESS SYNDROME This uncommon condition is thought to result when a calf is born too early, before its surfactant producing type 11 pneumonocyte cells in the lungs are mature. Affected individuals are born prematurely and are usually unable to stand. They have severe difficulty breathing. Severely affected cases die. Treatment will almost certainly be unsuccessful, although betamethasone, doxapram, clenbuterol and millophylline can be given. RESPIRATORY SIGNS WITH SEVERE NEONATAL CALF DIARRHOEA Calves with severe neonatal diarrhoea, particularly those which are recumbent, frequently have breathing problems. These signs are more likely to be the result of respiratory compensation for a metabolic acidosis following the neonatal diarrhoea rather than the result of an infectious pneumonia. However, calves with neonatal diarrhoea do sometimes develop acute exudative pneumonias and animals which have been in lateral recumbency for several days may develop the form referred to as hypostatic pneumonia. ACUTE EXUDATIVE PNEUMONIA It is usually considered that this syndrome is due to a primary bacterial infection of the lungs. Actinomyces pyogenes is the species most frequently isolated from these cases but Pasteurella species are also found, to a lesser degree. Calves which have suffered from severe neonatal diarrhoea seem to be particularly susceptible to this disorder. Prompt treatment with broad spectrum antibiotics usually produces a marked clinical improvement, but, in a small proportion of cases, recovery is incomplete and further episodes of pneumonia can occur. In a number of the latter cases chronic suppurative pneumonia develops. ASPIRATION PNEUMONIA This condition develops when a calf aspirates milk into the lower respiratory tract when being forced to drink milk from a bucket. Careless drenching of a sick animal, particularly when there is a degree of respiratory distress, can also produce the same syndrome. If the amount of fluid inhaled is small prompt antibiotic therapy will produce a clinical recovery. If a large amount has been inhaled and the animal does not die, it is likely to remain unthrifty because of the development of chronic pulmonary abscesses. This condition can be prevented by patiently coaxing calves to drink from a bucket. LUNG ABSCESSES These can follow incomplete recovery from one or more episodes of an acute exudative pneumonia. They can also arise as part of a septicaemia following navel ill, when they are usually multiple and in several lobes of the lungs. CONGENITAL CARDIAC DISEASE Complex congenital cardiac lesions may present with respiratory signs due to defective pulmonary circulation. Frequently, however, the respiratory signs are due to or exacerbated by a co-existing acute exudative pneumonia of an infectious nature. These animals may be smaller than normal and other congenital defects may also be present. At present, treatment is not possible for these cases.
PNEUMONIA IN HOUSED CALVES MORE THAN ONE MONTH OLD DEFINITION Respiratory diseases which are very common and economically very important in housed calves can develop suddenly or insidiously in individual animals as well as simultaneously in several animals within one group. While many infectious agents have been isolated from pneumonic calves, their individual importance is as yet unknown as is that of the many environmental factors which may affect the resistance of these calves. INCIDENCE The average mortality rate, in housed calves, resulting from pneumonia has been estimated at about 4 per cent. In many outbreaks, however, it can be considerably higher. EPIDEMIOLOGY Pneumonia in calves is important all over the United Kingdom. It occurs at all times of the year but there appears to be two specific peaks in incidence before Christmas and in the later winter/spring time. These increases in incidence could correspond to the periods of maximum numbers of susceptible calves. AETIOLOGY/ PATHOGENESIS A multitude of microbiological agents has been isolated from the lungs of pneumonic calves but their significance both individually and collectively has yet to be elucidated fully. It is possible that the infection rate and therefore the importance of the individual agents varies from year to year and from region to region. At present, the general view is that the mycoplasmas, parainfluenza virus (P13), respiratory syncytial virus (RSV), are the major pathogens. However, under certain circumstances, it is likely that many of the other agents frequently isolated from pneumonic calf lungs could exacerbate, if not initiate, respiratory disease since a large number of them can also be isolated from the healthy bovine lungs. The inability of agents isolated from pneumonic lungs to produce clinical disease has led to the concept of a ‘multiple factor aetiology" for calf pneumonia. In this concept the effect of potential respiratory pathogens is modified by the "stress" of other diseases or by physical factors e.g. chilling, wide fluctuations in environmental temperature, overcrowding or the mixing of calves from various sources. CLINICAL SIGNS Large numbers of similarly aged dairy and dairy cross calves are generally housed together and consequently share the same air space. Therefore, it is not surprising that infectious respiratory disease is so often a group problem although initially, individuals only may appear to be affected. The various respiratory syndromes will be described according to (a) the numbers of animals affected and (b) depending on the mode of onset of the clinical signs. Chronic Pneumonia Insidious onset, chronic pneumonia is a very common syndrome and there can be great variation in the severity of the disease in different groups of affected calves. In mild incidents, occasional coughing may be the only indications of the presence of respiratory disease. However, in severe outbreaks frequent bouts of coughing are common, almost all the calves in the group will have breathing difficulties with marked exercise intolerance when chased. Although affected animals are alert and maintain a good appetite, their growth rate is reduced and so an excessive difference in size develops between the calves.The rectal temperature which can show daily fluctuations, is usually below 103F. In the severe incidents the morbidity rate is almost 100 per cent but fatalities are rare in uncomplicated cases. Secondary bacterial infections are probably responsible for exacerbating some of the cases. In animals with severe complications, lung damage may not resolve but give rise to chronic coughing and unthriftiness. Severe acute exudative bacterial pneumonias may then prove fatal.Acute Pneumonia Sudden onset acute pneumonia frequently referred to as "virus pneumonia * or "enzootic pneumonia", can occur as a primary outbreak or probably more frequently as a complication of an existing chronic pneumonia. These incidents frequently arise within a couple of weeks, often after a few days, of calves being stressed in some way, e.g. by being mixed with different groups in a new house, or by being sold and transported to another farm. The severity of the clinical disease within an affected group varies greatly. The morbidity rate is generally less than 50 per cent on self-contained units but this can vary greatly. The highest rates e.g. up to 90% affected, are usually seen on units into which dairy calves at around three weeks of age are purchased in large numbers to be reared for beef. Overall, the mortality rate is usually low (<5%) but it may reach 10 per cent or even higher in particularly severe incidents.During their first winter housing period, several outbreaks of acute pneumonia can affect the one group of calves and it is often the same individuals which seem to be affected in these recurring outbreaks. Individual Problems Acute pneumonia can arise in individual animals either as a primary disease or as a complication of a chronic pneumonia. Recovered animals can suffer further pneumonic episodes and they eventually develop a severe chronic suppurative pneumonia. Affected individuals frequently die as a result of an acute exacerbation. DIAGNOSIS This is based upon the mode of onset of the clinical signs, the number of calves affected and the background history of the group. The findings at the post-mortem examination of fatal cases of calf pneumonia are often not very helpful in establishing the precise cause of the disease, particularly if it has been of an infectious nature. This is because firstly, the primary agent may have disappeared, or secondly, so few organisms may be present that they are unable to be detected by routine investigative procedures or thirdly there is almost invariably invasion by a number of secondary agents, especially bacteria. Even the isolation and identification of a known pathogen is not in itself absolute confirmation that it alone was the causal agent involved since many pathogens can exist in the lungs of healthy animals without necessarily producing disease. The use of paired blood samples, the first taken in the acute phase of the disease and the second in the convalescent phase some 2-3 weeks later, can identify active respiratory infection within a group of calves. Ideally, all animals at risk should be sampled. TREATMENT Mild chronic pneumonias may not be sufficiently severe to require treatment. However, when treatment is indicated the drugs of choice are long acting preparations of oxytetracycine and amoxycillin or tilmicosin. The treatment of calves suffering from acute respiratory disease must be undertaken promptly and, in virtually every incidence, without knowing the precise cause. Since it is usually assumed that severe clinical signs are the result of secondary bacterial infections, a course of drug therapy is usually begun; this almost invariably consists of the administration of a broad spectrum antibiotic. However, it must be borne in mind, that antibiotics do not have an inhibitory effect on viral multiplication.Recovery from acute pneumonia has considerably increased and the long-term damage to the lung has reduced by the use of flunixin. It is also beneficial for a pneumonic individual to be isolated in airy accommodation until it has recovered. CONTROL The following recommendations have been used successfully on several self contained dairy units to reduce to a minimal level, but not eradicate, the dual problems of calf scour and pneumonia:
If an outbreak of pneumonia develops, the calves born subsequently should be reared in a separate house as it is inadvisable to allow newly-born individuals to share the same air-space as animals suffering from obvious respiratory disease. In beef units into which calves are introduced regularly, the prevention of respiratory disease can be very difficult to achieve even when routine disease control measures are fully implemented. It has been claimed that when the incidence and mortality from respiratory disease threatens the financial viability of the enterprise, the only measure which will significantly reduce incidence of disease is a course of antibiotics given to every purchased calf during its first three days in the unit. However, it must be emphasised that this is the final step to be taken only after all other measures have been tried and have failed and it should not be considered as the first step in the control of calf respiratory disease.Unless the pneumonia is occurring at a very early age it is possible, and recommended to vaccinate the calves. Ask your veterinary surgeon for advice. |
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