Doi:10.1016/j.cvfa.2007.10.003

Department of Medical Sciences, University of Wisconsin-Madison School of Veterinary Medicine, 2015 Linden Drive, Madison, WI 53706, USA Besides stillbirths, disease is the most significant reason for mortality of dairy calves and heifers. Although reported mortality rates vary greatly byage, passive transfer status, type of operation, housing, season, manage-ment, country, region, and origin of the data set, enteritis and pneumoniaemerge as the most common reasons for disease-related deaths among dairycalves and heifers . Septicemia is an important cause of death in veryyoung calves diarrhea is the most important disease in calves lessthan 30 days of age and pneumonia is the most important problemin replacement heifers over 30 days of age The economic impact of dairy heifer replacement disease and death is sig- nificant. The cost of raising heifers at $1200 to $1600 or $1.40 to $1.88per day is high but is superseded by the cost of purchasing a springingheifer. Whether the goal is to maintain or expand herd size, disease manage-ment of dairy heifers is an appropriate focus for producers and their veter-inarian. In many dairy calf raising operations, the veterinarian’s role islimited to managing health problems, whereas most routine disease manage-ment, vaccinations, and treatment protocols are producer-driven. Althoughproducer recognition of the common calf disease concerns when validatedby postmortem examination is shown to be specific the sensitivity of de-tection is poor at 58% and 56%, respectively, for enteritis and pneumonia.
Early recognition and effective treatment of sick calves may reduce mortal-ity and address the concern of 40% of dairies that report having insufficientnumber of replacement heifers to maintain herd size .
This article presents veterinarians with a systematic approach to calf dis- ease investigations. Record analysis, colostrum and feeding protocols, hous-ing and bedding management, protocol reviews, diagnostic testing, and data 0749-0720/08/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.cvfa.2007.10.003 analysis are used to define problems, sources of infection, opportunities forimproving resistance, disease detection, and prevention.
Solving enteric disease problems of calves The investigation of herd-based calf diarrhea begins with an accurate un- derstanding of the age of onset, morbidity, and mortality data. For an en-demic herd problem, it is optimal to review 12 months of retrospectivedata. The minimum database includes the total number of calves born;the number of heifer calves alive at 24 or 48 hours (depending on whenthey leave the calving pen); the number affected; primary age-group affected;treatment history; and the mortality rate. For calf enteritis outbreaks, it isuseful to see at least 3 months of similar data. Calf records may not bekept or may provide minimal information but a review of the adult cow re-cords can provide enough information to calculate calf mortality rate. Pro-spective record keeping may be necessary and forms that are simple anduseful (can be provided to the dairy before the investigation. A ver-bal clinical history is necessary and important but the scope, which is fre-quently dominated by the most recent cases, requires some validationfrom a minimum of 3 months of records. Other records of potential impor-tance to the investigation are laboratory results from calf fecal specimens,blood cultures, tissue specimens, or postmortem examinations.
Most calf diarrhea problems are caused by a combination of factors, not all of which are infectious. The purpose of the herd investigation is to elu-cidate the potential enteric pathogens and to focus on the environment,calf immune status, nutrition, and management to define other contributingfactors. Colostral immunity is an essential part of enteric disease manage-ment and is discussed elsewhere in this issue. Most calf diarrhea herd prob-lems are caused by mixed infections and the agents may change overtime, depending on season of the year and population dynamics withinthe environmental site of exposure. By analyzing the fecal shedding patternsof calves in the affected age groups, potential pathogens can be identified.
Knowledge of the agents can better define sources or sites of exposure, Table 1Calf health records that elucidate age of onset, morbidity, and mortality DISEASE MANAGEMENT OF DAIRY CALVES AND HEIFERS can result in the development of more effective treatment plans, and can re-sult in more specific preventive recommendations.
To determine the potential enteric pathogens to which calves have been exposed, fecal specimens are obtained from untreated calves within theaffected age group. A good clinical history and calf health records providethe initial evidence for the age group of calves from which fecal specimensare obtained. The population at-risk can be confirmed by identifying theage of calves being treated for diarrhea on the day of the farm investigation.
Unless, the age-of-onset of diarrhea is in calves less than 5 days of age,diagnostic tests for enterotoxigenic Escherichia coli are not performed.
For calf diarrhea problems with age-of-onset between 5 and 14 days, theage group most commonly affected in most calf diarrhea investigations,samples are submitted for rotavirus, coronavirus, Salmonella spp, and Cryp-tosporidium parvum. Diarrhea problems in calves older that 14 days or inweaned heifers may include diagnostic tests for attaching and effacing Ecoli, Salmonella spp, Eimeria spp, and Giardia spp. Fecal samples are ob-tained from a minimum of six calves by inserting a gloved finger into the rec-tum carefully to extract feces that are present or by gently massaging therectal lining. Most calves defecate with the stimulation and the feces canbe collected into a 4-oz specimen cup. One should remove gloves beforesampling the next calf, clean the outside surface, and seal the cap of thespecimen cup. Four cotton swabs can be used to obtain a rectal smearfrom calves that do not produce manure. The calf identification, age or birthdate, and fecal consistency score are recorded as shown in . Samplehandling should follow the directions of the diagnostic laboratory receivingthe samples, but within 30 minutes of collection it is best to place feces forSalmonella culture into transport or selective Salmonella media like tetrathi-onate, selenite, or both. We bring media to the farm and inoculate each with Table 2Fecal examination and analysis from a calf diarrhea investigation with typical day of onsetat 9 days Where fecal score is 0 ¼ normal consistency; 1 ¼ semiformed or pasty; 2 ¼ loose but enough consistency to remain on bedding; 3 ¼ watery feces that sift through bedding material;B ¼ blood is present.
a 1- to 2-g (pea-size) portion of fresh feces. C parvum and viral samples canbe prepared according to the laboratory’s specifications. For acid-faststained smears, a dry cotton swab is dipped into the fecal specimen andthen used to make a thin fecal smear on each of two glass slides that are ap-propriately labeled and submitted for C parvum. The remainder of the fecalsample is submitted for rotavirus and coronavirus testing.
From expected level of exposure to potential fecal pathogens in the envi- ronment , it is anticipated that up to 20% of the calves sampled maybe shedding rotavirus, coronavirus, or C parvum. Fecal shedding of virus inorally vaccinated calves is uncommon so when two or more of sixcalves sampled are positive for the enteric viruses or C parvum or if anycalf is Salmonella spp positive, the exposure is considered abnormallyhigh. Enteric pathogens revealed in fecal shedding profiles can be validatedas the cause of herd diarrhea problems when intestinal microscopic lesionsdescribed in postmortem specimens are consistent with the pathogens pres-ent in the feces. As shown in , fecal shedding results show evidence ofincreased exposure to C parvum and Salmonella newport in a herd with calfdiarrhea problems in 9-day-old calves. Previous postmortem examinationsfrom the herd had demonstrated some intestinal villus blunting and clump-ing, consistent with C parvum infection, but the fibrino-purulent and necro-tizing enteritis from three recently examined dead calves had not been linkedto a Salmonella spp isolate. With abnormal fecal shedding patterns present,locating the source of infection is important and provides incentive to findsolutions that bypass, dilute, or distance calves from that site.
Finding the sources of infection for a dairy herd with calf diarrhea must take into account the health status of the dam, routes of infection of the poten-tial pathogens, the traffic pattern of the calves, incubation period of the poten-tial pathogens, and the behavior of calves. Sick and bacteremic calving cowsare more likely to have septicemic calves than calves with enteritis. Salmonelladublin carrier cows, whether or not they have clinical manifestations, are a highrisk for colostrum transmission of the disease to their calves, in which clinicaldisease is most common between 2 weeks and 3 months but can also occurat an earlier age. Most enteric pathogen transmission between the dam andcalf, however, occurs by fecal-oral spread by colostrum or the environment.
Even healthy cows have a large increase in fecal coliform bacterial counts dur-ing the periparturient period , putting the calves that commingle with cowsin the calving environment at much higher risk for enteric infection. Fecal-oraltransmission of enteric pathogens to calves can occur by contaminated bed-ding; commingled animals; pets; pests; colostrums; feeds; feeding utensils;esophageal feeders; or the hands, boots, or clothing of calf caregivers. Salivarysecretions from sick calves that reach the mouth of susceptible calves cantransmit Salmonella spp and other enteric pathogens, making the disposalof refused milk, water, and feed away from the calf environment an essentialaspect of disease management. Esophageal feeders, balling guns, clothing, andhands can facilitate salivary-oral transmission in a dairy herd experiencing calf DISEASE MANAGEMENT OF DAIRY CALVES AND HEIFERS diarrhea problems and must be cleaned and disinfected between successivecalf uses.
As the newborn calf moves from the birthing pen to its final preweaning home, every place of short-term occupancy is regarded as a potential sourceof infection. From the maternity pen to the warming or drying area, to thetransport vehicle or temporary hutch, all of the environments should beevaluated for enteric pathogens. Considering the percentage of time thatcalves most at risk for enteric infections spend lying the most likelyenvironmental source of an enteric infection is the bedding. Qualitativeassessments of bedding cleanliness are subjective, unreliable, difficult tocommunicate, and easy to dismiss. Objective data that can be reportedand compared with appropriate benchmarks provide motivation for change.
The concept of quantifying bedding bacteria as a risk assessment tool formastitis is well established, whereas the interest in identifying specificbacteria like multidrug-resistant Salmonella in bedding material is more re-cent but is useful for locating an environmental site of infection. Anevaluation of different calf bedding materials also demonstrates theuse of this approach to assessing disease risks in the environment wherecalves spend most of their time.
For herd problems of enteric disease in calves, bedding materials from each environment that has housed calves are submitted both for bacterialcounts (University of Minnesota Laboratory for Udder Health, MinnesotaVeterinary Diagnostic Laboratory, St. Paul, MN) and Salmonella spp cul-ture. Samples are taken with gloved hands from the perimeter of the penin each of the four quadrants and from the center of the pen, specificallyavoiding sampling fecal material. Samples for bacterial count are collectedin a sealable storage bag and stored in the refrigerator overnight before ship-ment to the laboratory. Bedding samples for Salmonella culture are placedin room temperature buffered peptone water pre-enrichment media, whichis sealed tightly and shipped overnight to the laboratory in biohazard bagcontainers. Bedding sample results from a dairy with diarrhea that startsin 5-day old calves is shown in . On that dairy, calves leave the ma-ternity pen, move to a currently unoccupied maternity pen hutch, fromwhich location they are taken by truck to a second farm, where they areplaced in a clean hutch. Because of a 1- to 2-day incubation period forthe fecal pathogens identified in the calves, bedding from a 3-day occupiedhutch is also sampled. From the data in , the bedding from the un-occupied hutch in the maternity pen and the truck are the most likely sour-ces of infection for the calves on that dairy.
For the enteric pathogens of most concern to calves, the incubation pe- riods range from 12 hours to 5 days. When a herd diarrhea problem affectscalves within the first 5 days of life, the source of infection is usually encoun-tered before the calf reaches its final preweaning pen. Alternatively, thesource of infection for diarrhea that begins after 7 days of age is usuallyfound in the calf housing area. The optimal bedding material for calves Table 3Bedding sample results from a dairy with diarrhea in 5-day-old calves depends on age of the calf, temperature, cost, bedding, season, and manage-ment. When granite fines, sand, rice hulls, long wheat straw, and wood shav-ings were compared performance indices were similar under themoderate temperatures of the study period but calves on sand and granitefines had more scours. Adding clean, dry bedding to maintain a minimumof 3 in between the calf and the base of the pen and the removal of allfeed refusals from the calf housing area are two very effective ways to diluteand distance calves from potential enteric pathogens. Continuous occu-pancy of calf raising facilities is a major risk factor that increases both thenumber and survival time of enteric pathogens in the environment. A goalof having 10% more calf pens than calves at maximum occupancy pro-vides time for cleaning, sanitizing, and resting pens between successive occu-pants. Strategic filling of calf raising facilities to empty large areas of thebarn, rather than a single row at a time, can reduce endemic enteric diseaseof calves. Disinfection protocols are useful if prior cleaning of facilities andpens has removed all organic debris; if the disinfectant is effective for theagents encountered in that facility; and if contact application, time, and sur-face are as specified. Safe, broad-spectrum disinfectants that can be used inhousing facilities, have penetration into soil or porous surfaces, can becross-protective for boots, and can be applied in novel ways lead to greatercompliance and improved calf disease management .
In addition to bedding contamination, other sources of enteric disease pathogens for calves are feeds, feeding equipment, pathogens on the skin,and the pen itself. Colostrum bacterial contamination is discussed elsewherein this issue. Milk replacer and pasteurized milk have a low risk for bacterialcontamination, especially fecal coliform bacteria, when there is proper mix-ing, storage, delivery, and feeding with clean equipment. Unpasteurizedwhole milk can present a high risk for enteric infection when it is nonsale-able milk that, if not fed immediately, has not chilled. To determine the levelof risk coming from the liquid feed, a bulk tank milk culture can be per-formed. Of most interest in reviewing the culture results is the total bacterialcount and the lactose-positive (fecal) coliform count. shows goalsand the ranges in milk and milk replacer bacterial numbers from bucket DISEASE MANAGEMENT OF DAIRY CALVES AND HEIFERS Table 4Bulk tank milk culture results from unpasteurized milk and milk replacer samples from dairieswith calf diarrhea problems or bottle samples obtained just before calf consumption in herds with calfdiarrhea problems (McGuirk, unpublished data, 2006). Culture swabs areused to assess cleanliness of feeding equipment, esophageal feeders, nipples,feeding bottles, and buckets for potential enteric pathogens. Only lactose-positive coliform growth is reported as evidence of inadequate sanitizingprocedures.
Self-grooming, a normal behavior of calves, can introduce enteric patho- gens from the skin of calves. Although this is not considered a major riskfactor for transmission of enteric disease, commingled calves, calves withcontact across open pen dividers, or calves housed in barns that arepower-washed while still occupied may be at risk. Aerosolized bacterialspread of enteric pathogens, although possible , is rarely the primarysource of enteric disease in calves.
A review of current vaccination, routine health management, and treat- ment protocols is an important part of enteric disease management in calves.
Colostrum management, as discussed elsewhere in this issue, is the most ef-fective way to transfer immunity to the specific enteric pathogens, entero-toxigenic E coli, coronavirus, rotavirus, and Clostridium perfringens typesC and D from vaccinated cows to newborn calves. Similarly, vaccinatedcows may transfer the benefit of gram-negative core antigen vaccine andsiderophore receptor porin S newport vaccine immunity to calves. Becausemost calf diarrhea problems occur within the first 3 weeks of life, immunecolostrum may be the only way effectively to protect young calves. The vac-cines labeled for administration to the young calf to aid in preventing diar-rheal diseases are limited and, with one exception (Entervene-d, FortDodge, Fort Dodge, Iowa), are administered at birth. Although many extra-label protocols attempt to improve the immunity of colostrum-deprived orsusceptible calves against diarrheal diseases, there is little scientific basis forsafety, efficacy, or disease protection. Where the veterinarian investigatingcalf diarrhea problems can be influential is in eliminating practices thathave potential to do harm or that make calves more susceptible to disease.
Avoid gram-negative bacterial vaccines not labeled for young calves. Do not vaccinate calves during times of stress or disease susceptibility, and be cau-tious about the use of multiple or frequent small vaccine doses. The focusshould be moved from vaccinating young calves to other means of reducingsusceptibility or improving their immune status.
Routine medications, feed additives, and well calf treatments should be reviewed closely in calf herds with enteric disease problems. Individually,feed additives like immunoglobulins, mannan oligosaccharides, coccido-stats, antibiotics, direct-fed microbials, immune modulators, charcoal,amino acids, and other ingredients may benefit calves, but unrestrainedcombinations, concentrations, and packaged remedies may change intestinalflora, transport time, digestibility, absorption, and intestinal health ofcalves. Simplicity and consistency is a good starting point for most calfhealth programs.
The treatment protocol for calf diarrhea is based on early and effective detection followed by appropriate intervention. Calves with diarrhea (fecalscore 2 or 3, with or without blood as described in ) should be iden-tified and currently on a treatment protocol. As part of a calf diarrhea inves-tigation, determine the disease detection rate by dividing the number ofcalves currently being treated for diarrhea by the number of calves with fecalscores 2 (loose but enough consistency to remain on bedding) and 3 (wateryfeces that sift through bedding material). The goal of an 85% or greater de-tection rate can be achieved by twice weekly fecal scoring of all calves 2weeks of age or less. In the detection of one of four calves with di-arrhea is below expectations.
Diarrhea treatment protocols for farm use must be straightforward and trainable. It should penalize neither the calf nor the person administeringtreatments. For compliance, it must be effective, frequently monitored, andupdated. The most important component of the treatment protocol is rehy-dration, and intravenous and oral fluid and electrolyte therapy of calveshave been reviewed Feeding calves through the course of diarrheamaintains caloric intake and adds fluid volume and electrolytes to supplemen-tal fluid administration. Continued feeding may facilitate the induction of di-gestive enzymes but may not be beneficial if force-feeding is required .
Therapeutic antibiotics are recommended for calves with diarrhea that havesigns of systemic illness . For the herd calf diarrhea protocol, criteriafor treatment is clearly established as any calf with a fecal score 2 or 3 as de-scribed in . If the examination of the calf reveals blood in the feces,a temperature greater than or equal to 103F, or the calf is dull, depressed,or off feed a 3-day course of antibiotics is started. If the diarrheic calfhas no signs of systemic illness, fluid therapy is the basis of the treatmentprotocol.
To encourage voluntary suckling, dividing the normal feeding volume into three or four smaller volume feedings may be better tolerated bysick calves. Milk or milk replacer is not given to diarrheic calves with a dis-tended abdomen or to one that is down and cannot be assisted to maintain DISEASE MANAGEMENT OF DAIRY CALVES AND HEIFERS sternal recumbency. Either a veterinarian is called or the recumbent calf isgiven intravenous fluid therapy. In addition to feeding milk, calves withdiarrhea need 2 (diarrhea score 2) or 4 qt (diarrhea score 3) of warm elec-trolyte solution each day. The electrolyte solution can be fed immediatelyafter (but not mixed in) the milk replacer or it can be fed at a time differ-ent than the milk replacer feeding. The approach I prefer is feeding fourtimes per day: 1 qt milk followed by 1 qt oral electrolyte solution at theregular morning feeding, at noon, again at the regular afternoon feeding,and last thing in evening. Alternatively, the four-time-a-day feeding sched-ule can provide two feedings for milk and two feedings for oral electrolytesolution for calves with a fecal score of 3. Oral electrolyte solution (alwaysmixed in water, not milk replacer) is fed until the diarrhea score returns to1 or 0. As the fecal consistency improves, the 2-qt electrolyte solution feed-ing can be placed between the two milk feedings. Fresh warm water shouldbe available to all calves but especially to diarrheic calves. Water is eitherfed at pleasure or within 20 to 30 minutes of a milk feeding so that calvesdrink before they leave the buckets to lie down.
The selection of a therapeutic antibiotic is based on the fecal culture re- sults or its gram-negative bacterial spectrum Once started, an anti-biotic protocol is not changed before the 3-day treatment is completed. Theantibiotic recommendation may look like one of the three extralabel proto-cols shown next.
1. Tribrissen (trimethoprim-sulfa tablets) Dose: 20 mg/kg ¼ 1 tablet (960-mg size) for a 100-lb calf twice daily.
Route: Oral, crushed and added to milk, crushed and dissolved in water–karo syrup combination, or bolus administered by ballinggun used slowly and gently.
1. Calves !2 weeks: two times daily for 3 days2. Calves 2–3 weeks: three times per day Dose: 5 mg/kg ¼ 4.5 mL for a 100-lb calf. This dose is 2.5 times the dose for respiratory disease and is specific for Salmonella.
Route: In the muscleFrequency: two times daily for 3 days Dose: 20 mg/kg ¼ 3 mL per 100 lb. Unlike the protocol for respiratory disease, calves with diarrhea receive a daily dose for 3 days.
Route: SubcutaneouslyFrequency: One dose daily for 3 days Treatment is successful if the calf is aggressively eating and has a bright attitude, even if the feces stay somewhat loose (score 1 or 2). It may take 5 to7 days for return to normal intestinal function and fecal consistency.
Solving respiratory disease problems of calves and heifers Pneumonia is responsible for 21.3% and 50.4% of preweaned and weaned heifer deaths, respectively, at an estimated cost of almost $15 percalf year . Despite the importance of the disease, early detection ishampered by use of diagnostic criteria that are poor predictors of pneumo-nia in the preweaned calf age group. Delayed diagnosis results in prolongeduse of antibiotics, a high recurrence rate, the development of refractory se-quelae, such as pulmonary abscessation, ear infections, and endemic herdproblems. Dairy calf and heifer pneumonia has serious economic conse-quences because subclinical, clinical, and chronic pneumonia of calves hasa negative impact on growth, reproductive performance, milk production,and longevity . Pneumonia is typically viewed as a postweaning prob-lem of dairy heifers but preweaned calves are frequently affected andare the source of pneumonia outbreaks in group pens. Early detection ofpneumonia is a significant problem in dairy calves, however, because typicalsigns of illness, such as depressed appetite, dull attitude, or an infrequentcough, are not exhibited.
In investigating a dairy calf or heifer pneumonia problem, the review of records to determine morbidity and mortality data, seasonal patterns,health, management, housing, number of calves at maximum occupancy,nutrition, vaccinations, procedures, case definition, and treatment protocolsis important. The site for disposal of liquid and solid feed refusals and penmanagement between successive calf occupants is also important. Calf hous-ing, with the number of calf pens or hutches, barn and pen construction, lay-out and dimensions, type, amount and condition of the bedding, calf trafficpatterns, and stocking density have an impact on respiratory disease that isdescribed elsewhere in this issue. Weaning parameters, age of weaning, androutine health management procedures are additional data of importance.
Tests for colostral immunity, infectious disease testing, and laboratory orpostmortem data are assembled and reviewed.
The true age of onset of respiratory disease and prevalence is determined on the day of the herd investigation using a respiratory disease screeningtool Individual calves in pens are examined and assigned a clinical scoreof 0 (normal), 1 (variation of or slightly abnormal), 2 (abnormal), and 3 (se-verely abnormal) for temperature, nasal discharge, cough and eye discharge,and ear position. Calves with a total respiratory score over 4 are consideredto have respiratory disease based on bronchoalveolar fluid cytology and cul-ture validation (McGuirk, unpublished data, 2007). All of the calves arescored if there are less than 20 calves. For larger groups, a representativesample up to 50 calves are screened by the scoring system to determinethe earliest age of onset and barn, pens, or location of most of the affectedcalves. In group pens, respiratory disease evaluations are similar but basedon the percentage of calves in the pen with abnormal ocular or nasal DISEASE MANAGEMENT OF DAIRY CALVES AND HEIFERS discharge, abnormal ears, or coughing as shown in . With comple-tion of the scoring examinations, a detection rate is calculated by dividingthe number of calves currently on treatment for respiratory disease by thetotal number of calves with a total respiratory score greater than 4. Aswith enteric disease, the goal is detection of at least 85% of the calvesthat require treatment, but this goal is rarely met until the farm is trainedto use the respiratory screening procedure. With digital thermometers thathave a 15-second reading time, an individual examination can be completedin less than 2 minutes per calf. Calves are easiest to examine between milkfeedings when they are resting. The nasal discharge, eye, and ear scorescan be assigned without entering the calf pen. Spontaneous coughing canalso be noted from outside the pen, giving the calf 3 points in that categoryand obviating the need to use tracheal compression for cough induction.
Proactive use of the respiratory scoring system improves early detection, pro-vides more reliable information on case rate, monitors for treatment efficacy,and determines which calves can move into the postweaning group pen.
Having identified the age of onset of respiratory disease through scoring, the youngest age group of affected calves is used for further diagnostic test-ing. If the goal of the investigation is simply to improve early detection andinitiate a more effective treatment protocol, nasal swabs are obtained fromsix untreated calves with respiratory disease. From each calf, two deep nasalswabs are taken using flexible culturettes that contain a transport system foraerobic and anaerobic bacteria (BBL Culture Swab Plus, Benton Dickenson,Sparks, Maryland). One of the swabs is submitted for bacterial cultureand the second is submitted for Mycoplasma bovis culture. From the nasalPasteurella multocida, Mannheimia haemolytica, and Histophilus somnus iso-lates, the antibiotics to which all isolates are susceptible are used to predict Table 5Respiratory disease evaluation in group pens on a dairy with pneumonia Group pen: % with abnormal (score 2 or 3) scores (goal: 10% or fewer in any category) the susceptibility of bacterial isolates from the lung If more than one ofsix calves cultures M bovis from the nose b-lactam antibiotics are notrecommended for the routine treatment protocol. From the nasal swab an-tibiotic susceptibility patterns shown in ceftiofur, florfenicol, tri-methoprim-sulfonamide combination, and tulathromycin are consideredsuitable for respiratory disease treatment if fewer than two of six calves cul-tures M bovis from the nasal swab. Prioritization of the antibiotic protocolsis based on the farm, age of calves being treated, compliance, acceptance,and cost of the drugs.
Bronchoalveolar fluid collection from preweaned calves in a herd with re- spiratory disease is a relatively efficient way to confirm and characterize thetype and severity of respiratory inflammation and provide fluid for bacterialculture. The bronchoalveolar fluid is collected from sedated calves usinga sterilized, flexible 10 Â 36-in French catheter with a 3-mL balloon cuff(Mila International, Medical Instrumentation for Animals, Florence, Ken-tucky). Five to 10 minutes after administration of 0.1 mg/kg xylazine intra-muscularly, the sedated calf is restrained and the nostrils are cleaned witha dry 4 Â 4-in gauze sponge. The head and neck of the calf are extendedto facilitate passage of the sterile bronchoalveolar catheter by a person wear-ing surgical gloves. Before catheter introduction into the nostril, sterile sa-line is dripped into the catheter to lubricate the guidewire stylette. Thebronchoalveolar catheter is introduced into the ventral meatus of the nosethrough which it is advanced until it encounters resistance in the caudalpharynx. At that point, the restrainer pushes the poll of the calf’s head ven-trally while simultaneously elevating the ventral mandible and the catheter isadvanced down the trachea during the inspiratory phase of the respiratorycycle. Repeated coughing is induced with proper catheter placement and it israpidly advanced until resistance is met as it wedges in a cranial lung lobebronchus. A failure to induce spontaneous coughing subsequent to passagebeyond the pharynx usually implies passage into the esophagus. In thewedged position, the catheter is held firmly in place while the guidewirestylette is removed. The balloon cuff is then inflated with 3 mL of air and Table 6Nasal swab bacterial isolates and antibiotic susceptibilities DISEASE MANAGEMENT OF DAIRY CALVES AND HEIFERS 120 mL of sterile saline is infused using 60-mL syringes with a stopcock andcatheter-tipped adapter attached. Immediately after the 120-mL infusion,negative pressure is applied to aspirate fluid, a process that usually yields10 to 40 mL of clear to mildly turbid, foamy fluid. The returned fluid sampleis placed into a sterile 4-oz specimen cup. A second 120-mL infusion is in-troduced and aspirated as described and the pooled fluid is sealed in thespecimen cup and preserved in a cooler until it can be processed. The freshbronchoalveolar fluid sample is processed within 2 hours of collection or re-frigerated until it can be analyzed. A 5-mL aliquot of the pooled sample isused for bacterial and Mycoplasma cultures. The remaining fluid is submit-ted for cytologic interpretation, which is based on routine staining of cyto-spin and direct smear preparations. Bronchoalveolar fluid that yieldshomogenous (O106 CFU/mL) bacterial or positive M bovis culture is con-sidered abnormal. A disproportionate lowering of macrophages (!61%) orelevation of neutrophils (O39%) provides evidence of an inflammatory re-sponse with or without a positive culture (McGuirk, unpublished data, 2007).
The ability to troubleshoot respiratory problems in calves is hampered if the problem is not respiratory disease; the methods for and detection of theproblem are neither sensitive nor specific; or the treatments use inappropri-ate drugs, routes of administration, dose administered, duration of therapy,or storage. The perceived problem of high morbidity or poor cure rates maybe a problem of poor disease definition, inaccurate diagnosis, overwhelmingexposure, unusual susceptibility, ineffective treatments, or a combination ofthese factors.
Respiratory disease management of calves and heifers is not complete without a thorough review of the vaccination protocols for the herd. Withpreweaned respiratory disease problems, the emphasis is placed on vaccina-tion of the adult cows and an effective colostrum feeding program. As moreand more is learned about the effectiveness of vaccinating calves for respira-tory pathogens in the face of maternal immunity, vaccination of preweanedcalves may become more common . Where colostral immunity is consis-tently good, most dairy heifers have the first modified live virus vaccines at3 or 4 months of age. In the absence of adequate colostral immunity, earliervaccination schedules have been instituted and, at least for viral respiratorypathogens, are relatively safe.
Respiratory disease investigations present three opportunities to reduce endemic problems in calves and heifers. Regular implementation of a screen-ing examination can find calves at an early age when treatment is extremelyeffective. Scoring calves after a 5- or 6-day treatment protocol can determinewhich calves are cured and which require additional treatment. Calvesscored before moving into a group pen can result in fewer uncured pneumo-nia cases causing a respiratory disease outbreak in the weaning pen. Nasalswab results can guide the implementation of effective treatment protocolsand bronchoalveolar fluid can more specifically characterize respiratory in-flammatory changes. Finally, characterizing and resolving calf housing risk factors for respiratory disease can reduce the exposure to aerosolized bacte-ria and lower the prevalence of respiratory disease.
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