DAIRY CALF PNEUMONIA : EFFECTIVE TREATMENT DEPENDS ON EARLY AND ACCURATE DIAGNOSIS

Dairy calf pneumonia is one of the most economically important diseases of calves. A delayed diagnosis could result endemic herd problem, prolonged use of antibiotics, high recurrence rate, pulmonary abscessation and ear infections. The key for effective control is the early detection of pneumonia and the accurate diagnosis of the etiologic factor. For the early detection, a respiratory disease score was assigned based on rectal temperature, character of nasal discharge, eye discharge or ear appearance, and presence of a cough. Each clinical sign has a point scale from 0 (normal) to 4 (severe). The respiratory disease score is the sum of points from the 4 categories of clinical signs, with increasing values representing progressive severity. The scoring system results in a minimum score of 0 and a maximum score of 12. Calves with score 5 or higher, having at least 2 clinical signs of respiratory disease, are considered sick and have to be treated. For the accurate diagnosis of the etiological agent the best tool in a live calf is bronchoalveolar lavage (BAL) fluid collection. Sampling of severely affected animals should be avoided. New acute cases are ideal. BAL is performed in sedated calves using a sterilized, flexible catheter with a 5-cc balloon cuff. The fresh BAL fluid sample is processed within 2 hours of collection or refrigerated until analysis. Part of the sample is used for microbiology and the remaining is submitted for cytology. BAL fluid that yields homogenous (>106 CFU/ml) bacterial or positive Mycoplasma bovis culture is considered abnormal. A disproportionate lowering of macrophages (<61%) or elevation of neutrophils (>39%) provides evidence of an inflammatory response with or without a positive


Risk Factors / Faktori rizika
Diagnosis / Dijagnoza result, the affected-uncured calves enter the weaning pens and could lead to endemic herd problem.
The keys for effective pneumonia control are the early detection (clinical diagnosis) and the accurate identification of the causative agents (with the implementation of ancillary tests).

Clinical diagnosis
The clinical signs of fever, nasal discharge, lacrimation, cough, increased respiratory rate, depression, reduced appetite, rough hair coat, weight loss and abnormal lung sounds rarely occur together, may be absent in early cases of pneumonia, are easily overlooked by caretakers, and require time and advanced knowledge to detect, even for clinicians (McGuirk, 2005).Farmer diagnosis of pneumonia fails to identify as many as 50% of affected calves and, when identified, is typically 4 to 5 days after onset (Virtala et al., 1996;Quimby et al., 2001).Better indicators in the very early stages of pneumonia are the prolonged time the calves spend in the buckets and the longer standing after drinking.
Since the criteria used in the field are poor predictors of disease, early diagnosis of dairy calf pneumonia is frequently missed, along with the opportunity to make effective treatment interventions or recognize important herd problems before significant losses are incurred.
A simple and practical respiratory scoring system for early detection of pneumonia in dairy calves individually has been validated (McGuirk et al., 2007).At best, when implemented regularly twice weekly in pre-weaned calves kept in single pens, it has been the most effective tool in eliminating endemic pneumonia.At least, it should be performed at critical times, such as at the pneumonia onset in a farm or just before weaning.It is based on: 1. rectal temperature, 2. the character of nasal discharge, 3. eye or ear appearance, and 4. presence of a cough (McGuirk, 2005).As it is shown in Table 1 (Lago et al., 2006), the respiratory disease score is the sum of points from the 4 categories of clinical signs, with increasing values representing progressive severity.
Eyes and ears are evaluated but only the highest value is entered into the score.For example, if the eye score is 1 and the ear score is 2, the ear score of 2 is entered.The scoring system results in a minimum score of 0 and a maximum score of 12.The total score determines the outcome.Calves with score 5 or higher have at least 2 clinical signs of respiratory disease, and thus are considered sick and have to be treated (McGuirk, 2005;Lago et al., 2006).

Ancillary diagnostic tests
It is widely accepted that the most commonly isolated microorganisms in dairy calves respiratory disease complex are the following: a. Bacteria: Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, Mycoplasma bovis, Mycoplasma dispar and the non-primary pathogens Actinomyces pyogenes.
Many of them are normal flora of the upper respiratory tract (Watts et al., 1994), but they introduce respiratory disease when they colonize the lower respiratory tract (trachea and lungs) (Divers, 2008).
Seroconversion to a specific viral respiratory pathogen has considerable drawbacks with time delays to obtain convalescent samples and concomitant seroconversion to infectious agents that have not caused the disease (Pringle, 1992).
The diagnostic techniques that could be applied to collect the appropriate samples in order to identify the microorganisms involved are: nasal swab, trans-tracheal wash and bronchoalveolar lavage (BAL) fluid collection.Transtracheal washing obtains samples from the lower respiratory tract bypassing the nasopharynx (Pringle, 1992), but is the most difficult to implement in the field as it requires surgical preparation of the ventral surface of the neck.Due to the more invasive nature it is less suitable for routine field investigations (Caldow, 2001).Nasal swab is easy to perform and particularly useful in detecting acute viral infections, such as IBR; it can also be an indirect indicator of pathogens in the lower respiratory tract (Pringle, 1992).The concern is that, as mentioned above, many of the isolated microorganisms are just normal commensals of the upper respiratory tract (Caldow, 2001).However, they can be successfully used for an antibiogram in group level (multiple cases).For the accurate diagnosis of the etiological agent in a live calf (either in field or in clinic), the best tool is the BAL fluid collection.It requires a little training, but is safe and efficient.Although it can be performed using fiberoptic endoscopes, more rudimentary equipment (commercially available catheters) can successfully be used (Pringle, 1992;Caldow, 2001;Jackson and Cockcroft, 2002).
Sampling of severely affected animals should be avoided, because of the added stress caused by the procedure.New acute cases, before any antibiotic allowance, are ideal.This technique is usually used when there has been an outbreak of pneumonia with high morbidity.In order to obtain an accurate profile of the etiological agent it is advisable to select up to five animals for sampling (Jackson and Cockcroft, 2002).
BAL is performed in sedated calves using a sterilized, flexible 10 French x 36 inch catheter with a 5-cc balloon cuff (Urinary catheters, Foley catheters, Mila International Inc., Medical Instrumentation for Animals, Florence KY, USA).Five to 10 minutes after administration of 0.1 mg/kg xylazine IM, the sedated calf is restrained and the nostrils are cleaned with a dry gauze sponge.The head and neck of the calf are extended to facilitate passage of the sterile BAL catheter by a person wearing surgical gloves.Prior to catheter introduction into the nostril, sterile saline is dripped into the catheter to lubricate the guide-wire stylette.The BAL catheter is introduced into the ventral meatus of the nose through which it is advanced until it encounters resistance in the caudal pharynx.At that point, the restrainer pushes the poll of the calf's head ventrally while simultaneously elevating the ventral mandible and the catheter is advanced down the trachea during the inspiratory phase of the respiratory cycle (McGuirk and Peek, 2007).
Repeated coughing is induced with proper catheter placement.The catheter is rapidly advanced until resistance is met as it wedges in a cranial lung lobe bronchus.Failure to induce spontaneous coughing subsequent to passage beyond the pharynx usually implies passage into the esophagus.In the wedged position, the catheter is held firmly in place while the guide-wire stylette is removed.The balloon cuff is then inflated with 5 cc of air and 120 ml of sterile saline is infused using 60 ml syringes with a stopcock and catheter tipped adapter attached.Immediately after the 120 ml infusion, negative pressure is applied to aspirate fluid, a process that usually yields 10 to 40 ml of clear to mildly turbid, foamy fluid.The returned fluid sample is placed into a sterile 120 g specimen cup.A second 120 ml infusion is introduced and aspirated as described and the pooled fluid is sealed in the specimen cup and preserved in a cooler until it can be processed (McGuirk and Peek, 2007).
The fresh BAL fluid sample is processed within 2 hours of collection or refrigerated until it can be analyzed.A 5 ml aliquot of the pooled sample is used for bacteria cultures and identification of viral antigens.The remaining fluid is submitted for cytological interpretation, which is based on routine staining of cytospin and direct smear preparations (Jackson and Cockcroft, 2002).Organisms that have been found in association with disorders of the respiratory tract, alone or in combination, from BAL fluid samples of dairy cattle are Mycoplasma bovis, Mannheimia haemolytica, Pasteurella multocida, Histophilus somni and Salmonella dublin, IBR, BRSV and PI 3 (Tegtmeier et al., 1999;Kokotovic et al., 2007).BAL fluid that yields homogenous (>10 6 CFU/ml) bacterial or positive Mycoplasma bovis culture is considered abnormal.Cells in BAL of the normal cattle are predominantly alveolar macrophages (Pringle, 1992).A disproportionate lowering of macrophages (<61%) or elevation of neutrophils (>39%) provides evidence of an inflammatory response with or without a positive culture (McGuirk and Peek, 2007).
Respiratory disease is treatable in calves that score 5 points or more using the Calf Respiratory Scoring System (Table 1).Calves with a score of 5 or more should be treated with an antibiotic protocol that provides 5-6 days of coverage.At the end of the 5-6 days treatment protocol, the calf is scored again.If the respiratory score is 3 or lower, the calf is considered cured and no further treatment is needed.If the calf is scored 4, it should be rechecked the following day.Persistence of score 4 warrants a second course of the antibiotic.Score 5 or higher should enter a second protocol (McGuirk, 2007).

Normalno
Ear flick or head shake /

Jednostrana klempavost uha
Head tilt or bilateral ear drop /

Nagnuta glava ili obostrana klempavost u{iju
The response to treatment depends on early detection, correct choice of antibiotic, activity of drug at site of lesion, penetration of drug into exudate and route, dose and duration of therapy.The ideal antibiotic selection would be based on the antibiotic susceptibility pattern of lung pathogens preferably after BAL fluid culture (for individual cases and in group level) or alternatively, if BAL is difficult or impossible to perform, nasal swabs culture.In an individual calf, nasal swabs culture do not accurately predict BAL culture.The nasal swabs and BAL culture results are quite similar at group level, however (Allen et al., 1991;Caldow, 2001).
From information that has gained culturing BAL fluid or nasal swabs collected from many farms with dairy calf pneumonia in Wisconsin USA, it is anticipated that the following antibiotics will be effective in calves with pneumonia that are diagnosed early (McGuirk, 2007): 1) Ceftiofur: 2.2 mg/kg IM, frequency: once per day for 5 days; 2) Oxytetracyline L.A. 200: there is resistance now for P. multocida and M. haemolytica.Dose: 20 mg/kg SC, frequency: once per day, every other day for 5 days (3 doses); 3) Florfenicol: 40 mg/kg SC, frequency: once every other day for 3 doses (6 day total course of treatment); 4) Tilmicosin: 10 mg/kg SC, frequency: once per day, every third day for 5 days (2 doses); 5) Tulathromycin: 2.5 mg/kg SC, frequency: once per day, every third day for 5 days (2 doses).
When Mycoplasma bovis is cultured from <17% of the nasal swab cultures, it is presumed that it is not the primary etiologic agent and antibiotic selection is based on susceptibility results from positive (>10 6 cfu/ml) BAL cultures and/or the susceptibility patterns of Pasteurella multocida, Mannheimia haemolytica and Histophilus somni isolates from the nasal swabs (McGuirk, 2005).The composite nasal swab antibiotic susceptibility results from herds with concurrent dairy calf pneumonia and otitis in a 2005 survey are shown in Table 2. Mycoplasma susceptibilities are not performed routinely in many laboratories.Field strain resistance is problematic leaving only the 3 fluoroquinolones (danofloxacin, enrofloxacin and marbofloxacin) with consistent efficacy (Francoz et al., 2005;Thomas et al., 2003).Tiamulin has demonstrated efficacy against most M. bovis field isolates (Thomas et al., 2003;Hirose et al., 2003).M. bovis is less susceptible to spiramycin, oxytetracycline, tetracycline, tylosin, lincomycin, florfenicol, gentamycin and spectinomycin (Loria et al., 2003;Hirose et al., 2003;Francoz et al., 2005).Erythromycin and tilmicosin resistance to M. bovis has been found by some, while tylosin effectiveness has been noted by others (ter Laak et al., 1993;Ayling et al., 2000;Loria et al., 2003;Francoz et al., 2005).
Of course, it is important to notice that the appropriate treatment for respiratory diseases is subdivided in 2 major parts: the "etiological" therapy (antibiotic allowance against bacteria) and the "supportive" therapy, which is very important to implement.The latter mainly consisted of (Divers, 2008): 1. Non-steroid anti-inflammatory drugs (preferably) or corticosteroids (once): to reduce fever, inflammation and pain and for their action against endotoxinosis (mainly is caused by M. haemolytica infection); 2. Fluids and electrolytes IV: to restore dehydration and to correct the electrolyte imbalances (respiratory alkalosis or acidosis); 3. Bronchodilators; 4. Mucolytics.Furthermore, injection of vitamin E and selenium would be beneficial, for their antioxidant properties and boosting of immunity.
Finally, it is very important to remember the vital role ventilation plays for the respiratory disease complex of dairy calves.In any case, ventilation deficiencies should be corrected.