Pneumonia in adult dairy cattle (Proceedings)

Respiratory disease continues to present challenges in the dairy industry in the 21st century. Traditionally, veterinary curricula have emphasized an etiologic approach to the subject and veterinary practitioners are very familiar with the well documented and heavily researched infectious causes such as bovine respiratory syncytial virus (BRSV), infectious bovine rhinotracheitis (IBR), bovine viral diarrhea virus (BVDV), Mannheimia haemolytica, Pasteurella multocida and Mycoplasma spp. It is no coincidence that these well documented forms of respiratory disease are the ones for which commercial vaccines are widely available and heavily utilized. Despite a good understanding of these primary causes of bovine respiratory disease and widespread compliance with established herd vaccination protocols, it is still common for veterinarians to be asked to trouble shoot outbreaks of respiratory disease in adult dairy cattle.

Veterinarians are comfortable with the clinical signs that classically accompany infectious lower airway disease, namely tachypnea, pyrexia, nasal discharge and coughing as well as the auscultation of adventitious lung sounds. Unfortunately, some of these clinical signs, particularly pyrexia, tachypnea and nasal discharge are not specific for pneumonia. An elevated body temperature in an adult dairy cow is not always a true fever but is almost always accompanied by a compensatory increase in respiratory rate that, taken together, frequently result in a diagnosis of pneumonia, especially amongst non-veterinarians. A rectal temperature greater than 103 °F is usually ascribed to fever in adult dairy cattle, the root of which may be infection, inflammation or an immune response. Increased environmental temperature, elevated temperature/humidity index, exercise, and/or heat exposure (limited access to shade, shelter or fans) are other reasons for hyperthermia in cattle. If one adds some degree of nasal discharge to a cow with hyperthermia, perhaps attributable to nothing more than a reluctance to clean off her nose as is common in cattle with any number of conditions, it may be surprising that pneumonia isn't diagnosed even more frequently than it is. We find that "pneumonia" becomes an escape diagnosis for all cattle with fever and tachypnea, signs that may accompany other diseases. Individuals in the fresh cow pen that demonstrate a fever in the absence of uterine discharge/odor, abnormal mammary gland evaluation or diarrhea are all too frequently assigned this diagnosis. However their signs may be nothing more than the normal physiologic response to fever with an increased respiratory rate or effort. To complicate a pneumonia diagnosis further, finding a normal temperature in cattle does not necessarily rule out an infectious or inflammatory response and many cows with chronic pneumonia have no fever.

Thoracic auscultation is both an art and a science and, as such, is subject to a variety of interpretations, even amongst trained veterinarians. Pneumonia in adult dairy cattle may not be associated with auscultation of classical crackles and wheezes when there is pulmonary consolidation, abscessation, pneumothorax, or pleural fluid accumulation. Increased intensity of thoracic breath sounds, when not based on a comparison to tracheal breath sound intensity can simply be the result of rapid breathing, proximity to the hilus or thin body condition of the patient. Stethoscope quality, the listening environment, cow temperament, thoracic wall thickness or body condition of the cow can also impair the potential value of lung auscultation. While thoracic auscultation can be a valuable tool in the hands of a trained veterinarian examining a cow suspected to have pneumonia, we find no substantive value in making thoracic auscultation a routine part of the examination of adult cattle by lay persons working the fresh or hospital cow pen on the dairy.

On farm we recommend establishing a clear case definition to avoid over, or under, detection of adult cow respiratory disease. Along with clear guidelines that allow farm workers to identify the cows that need to be examined more closely, train them to consistently apply and interpret a limited number of clinical observations and examination parameters. Make time to work with the dairy at least monthly to observe, solidify and enhance good health screening practices and to reinforce responsible treatment protocols and procedures. Relative to respiratory disease of adult dairy cows, some reasons to pull cows for a more detailed examination include the following:

     • Cow didn't lock up

     • Milk weight deviation from previous milking

     • Abnormal udder fill

     • Recheck exam (cow with fever, reduced appetite or no diagnosis previous day)

     • Cow standing with head and neck extended

     • Cow is breathing with mouth open

     • Cow has labored breathing, inspiration or expiration

     • There is undisturbed feed or disproportionate feed consumption compared to other cows in the group

     • Cow has colored (white, yellow, green, brown, bloody) or thick nasal discharge

     • Cow is coughing

     • Cow has foul smell to her breath

In general, the examination parameters that can be consistently taught and then applied and evaluated by non-veterinarian farm personnel are the following:

     • From behind the cow,

          o Rectal temperature, using a digital thermometer with adequate (~ 4 inch) probe length

          o Fecal consistency

          o Vaginal discharge

          o Udder symmetry, size, color

          o Rumen evaluation – palpable contraction within 30 seconds

     • From in front of the cow

          o Character of the nasal discharge

          o Presence of a cough – spontaneous or inducible

Based on the interpretation of the above findings, a respiratory disease treatment protocol is instituted if 2 or more of the following clinical signs are present.

     • Fever > 103°F

     • Abnormal nasal discharge

     • Cough - spontaneous

Treatment of respiratory disease in adult dairy cows is relatively straight forward and should involve the use of antibiotics labeled for pneumonia and approved for lactating dairy cattle. The goal is to provide 5 to 7 days' duration of coverage. With ampicillin, ceftiofur, penicillin, oxytetracycline and sulfadimethoxine amongst the products from which to choose, the veterinarian should establish a protocol that fits best with the dairy. A good protocol is simple and specific (dosage, route, frequency and duration of treatment). Criteria for ending treatment, changing the antibiotic, adding anti-inflammatory drugs or calling the veterinarian should be clearly established.

In the face of a reported group respiratory disease problem amongst adult dairy cattle, it is important to confirm the diagnosis by your own examination. It is rare to find a straight forward single agent exposure followed by disease picture, leaving important details of pen size, number, age, stage of lactation and vaccination status of pen occupants critical when trouble shooting an outbreak. Pen move frequency, sequence of moves, duration of stay in a pen, and animal additions are further details to be deciphered. Inquiries as to the source, quality, quantity, and delivery of feeds along with measurement of bunk space, water availability, water quality, space for drinking and air quality evaluation can reveal the stressor(s) that is (are) frequently the trigger in adult dairy cattle respiratory disease outbreaks.

Diagnostic testing may elucidate the etiologic picture that emerges from a respiratory disease outbreak. Although some veterinary practitioners have great confidence in the value of serologic testing, we find little value in serology. It can be challenging to obtain convalescent samples from the same individuals from which acute samples were taken two weeks previously or to sample at the optimal time to find a four-fold increase in titer on farm. Interpretation of results is complicated by vaccination status, age, and immune response of the cows, not to mention the differences amongst the viruses being tested. Aspiration of tracheal fluid (transtracheal wash) can provide valuable information about the bacterial and/or viral etiology in acute and untreated cattle but is invasive in nature and inefficient relative to the number of cows that can be sampled, limiting its use for solving herd-based disease problems. We have used bronchoalveolar fluid lavage (BAL) as an effective diagnostic tool for evaluation of respiratory disease outbreaks in adult dairy cattle but specialized equipment is needed. The BAL fluid cytology, culture (conventional aerobic bacteria as well as Mycoplasma culture) and virus isolation results can be useful for determining etiology and pathophysiologic mechanism of disease.

Bronchoalveolar lavage (BAL) is performed in sedated cows using a sterilized, flexible BAL tube (Bivona®– 3 meter length, 11 mm outside diameter, 5-cc balloon cuff; call 800-258-5361 to order). Five to 10 minutes after administration of 0.08 mg/kg xylazine IM, the sedated cow is restrained and the nostrils are cleaned with a dry 4X4 gauze sponge. Prior to catheter introduction into the nostril, the integrity of the balloon is tested by introduction of 5-cc of air. The balloon is deflated and the sterile BAL catheter is introduced into the nostril and directed into the ventral meatus by a person wearing sterile gloves. The BAL catheter is advanced until it encounters resistance in the caudal pharynx. At that point, the restrainer maximally extends the head and neck of the cow while simultaneously keeping the neck straight. The catheter is passed rapidly into the trachea during the inspiratory phase of the respiratory cycle. Repeated coughing is induced with proper catheter placement and it is then 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 of the tube into the esophagus. In the wedged position, the balloon cuff is inflated with 5 cc of air, a 3-way stopcock is inserted into the end of the BAL tube and 240-ml of sterile saline is infused using 60-ml syringes. Immediately after the 240 ml infusion, negative pressure is applied to aspirate fluid, a process that can yield up to 120 ml of mildly turbid, foamy fluid. Mucus and purulent flecks may be visualized and some samples are slightly blood-tinged. The returned fluid sample is placed into sterile 4 to 8 oz specimen cups. A second 240-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. When fluid collection is finished, the balloon is deflated completely and the catheter removed from the nose. The fresh BAL fluid sample is processed as soon after collection as possible. If it is not processed within 2 hours of collection, it can be refrigerated until submission of samples. A 5-ml aliquot of the pooled sample is used for bacterial and Mycoplasma cultures. A similar fluid aliquot can be submitted for BRSV ELISA or PCR testing. The remaining fluid is used for cytological interpretation, which is based on routine staining of cytospin and direct smear preparations. BAL fluid that yields homogenous (> 106 CFU/ml) bacterial or positive Mycoplasma bovis culture is considered abnormal. A disproportionate lowering of macrophages (< 80%) or elevation of neutrophils (>20%) provides evidence of an inflammatory response with or without a positive culture.

Our clinical experiences also suggest that many cases of "pneumonia" in adult cattle are actually chronic disease cases at the time of first diagnosis, further complicating the subject of respiratory disease in adult cattle by inferring the potential for missed early diagnosis and treatment intervention. This chronicity may evolve from prior episodes of pneumonia during times of lesser scrutiny, such as late lactation or the dry period when the disease was mild, clinically occult or just missed, or perhaps relate to pre-existent calfhood respiratory disease from which recovery was partial, or that left the individual with compromised lower airway clearance and lung parenchyma. Notionally, calves may be able to compensate well for this pathology until the rigors of lactation, periparturient immune suppression, heat stress and pathogen exposure combine. The degree to which calfhood pneumonia predisposes individuals to adult respiratory disease is unknown/unvalidated at this time but our own personal, regional observations alongside national surveillance schemes for calfhood morbidity would suggest an increasing issue with calf pneumonia in modern dairying.

Much of the preventative approach to respiratory disease in dairy cattle has historically focused on vaccination strategies for acquiring and maintaining immunity to several of the infectious pathogens mentioned above. Undoubtedly, herd protection against BRSV, IBR and BVDV can be dramatically improved by appropriate primary course and booster vaccines against these viruses and there have been some recent advances in the efficacy and utilization of these products that will be discussed. It is important to bear in mind that vaccination contributes just one part of an overall herd preventative medicine program that needs to retain consistency on many fronts to maintain excellence. Biosecurity, in the form of screening, quarantine and appropriate vaccination for purchased additions and returning replacement stock are other key components in the battle against contagious respiratory disease in the herd. Vaccines against bacterial agents such as Pasteurella multocida, Histophilus somnus, Mannheimia haemolytica and Mycoplasma spp., although readily available, and frequently used, do not enjoy the same evidence based medicine support as do their viral counterparts. Another uncertain area scientifically is that of vaccination in the face of an outbreak of presumed or proven, respiratory disease, and the pros and cons of this will also be discussed.

Air quality and adequate ventilation, now quite well established as prime determinants of respiratory health in calf facilities, are in our estimation, similarly relevant in the discussion of respiratory disease in adults. Although quantification and evaluation of ventilation in dairy barns is by no means widespread, nor easy, there are facility level issues as well as cow level (stocking density, overcrowding) issues that can negatively impact air quality and inhibit both immunologic and non-immunologic airway defense mechanisms.

In conclusion, respiratory disease in adult cattle should be thought of in broader terms than just the traditional contagious pathogens and the available vaccines against them. An integrative approach that considers factors that significantly influence host immune responsiveness to pathogens and vaccines should be taken alongside as refined and as astute a diagnostic/surveillance approach as can be achieved practically. This presentation will utilize information gleaned from actual investigations of respiratory disease on dairy farms to illustrate the value of early, but accurate detection of respiratory disease in adult dairy cattle as well as the diagnostic steps, vaccination protocol review, therapeutic principles that may be useful to trouble shooting respiratory disease problems in adult dairy cattle.

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