Prevention and Control of Undifferentiated Ruminant Respiratory Disease

Amelia R. Woolums

Vaccines are available to prevent or limit disease due to several respiratory pathogens, and proper use of vaccines is an important component of any management effort to minimize ruminant respiratory disease.

MANAGEMENT PRACTICES TO MINIMIZE DAIRY CALF RESPI­RATORY DISEASE. Efforts to minimize respiratory disease in calves should begin with assessment of factors that may be impairing host defense mechanisms, which were outlined above. Ensuring adequate transfer of maternal antibodies to newborn calves by appropriate colostrum handling and administration is one of the practices most important to ensuring calf health. On farms with high rates of calf respiratory disease, particulary in calves in the first month or two of life, efforts to address respiratory disease should include assessment of transfer of passive immunity in calves within the first week of life. If rates of failure of transfer of passive immunity are unacceptably high, management practices should be corrected to address the problem.

Although transfer of passive immunity is important to ensure calf health, groups of dairy calves with adequate transfer of passive immunity can still have high rates of respiratory disease. Thus other risk factors must also be assessed on dairies with unacceptable rates of calf respiratory disease. The method of calf housing has an important impact on risk for respiratory disease. Commonly used dairy calf housing includes individual calf hutches outdoors, super hutches for small groups of calves outdoors, individual calf pens inside a building, and group calf pens inside a building. Respiratory disease is less common in calves housed in individual hutches outdoors as compared to calves housed in individual pens indoors or in group pens indoors.^9,40 In spite of this, many producers house calves in individual pens or group pens indoors because of the negative impact of weather extremes on calves housed outdoors in hutches and on their caretakers.

Standards for ventilation of calf housing have been reported (see Box 31.5). A study evaluating respiratory disease prevalence in calves housed in individual pens in naturally ventilated barns⁹¹ found that respiratory disease prevalence was decreased on farms where pens had lower total airborne bacterial counts, solid barriers between calves, and bedding that was deep enough for calves to nestle into (so that their legs could not be seen when they were lying down). Because having four or more solid partitions around a calf increased total bacterial counts in pen air, solid partitions should be placed between calves but on no more than three sides; on the front, back, and top of calf pens, mesh barriers should be used.

Calf housing with stocking densities that are too high may result in increased transmission of pathogens, especially if there is mixing of calves of a wide age range. Overcrowding also puts additional stress on the building ventilation through buildup of noxious gases and pathogens. Cleaning of calf crates with high-pressure water sprayers is associated with new cases of pneumonia several days later. Bates and Anderson⁹² have recom­mended standards for ventilation, including building location, fan capacity and location, intake location and design, tempera­ture regulation, air space needed and airflow directions, and acceptable humidity levels. Sivula and colleagues⁴¹ found that 80% of calf barns provided housing that failed to meet adequate standards of ventilation and housing regardless of whether calves were housed individually or in groups.

Nutritional problems that can predispose calves to disease include deficiencies of energy, protein, vitamins, or minerals necessary for the immune response. Deficiencies of copper, selenium, zinc, manganese, iron, and vitamins A and E are of special concern. Dairy managers sometimes create energy and protein deficiencies by feeding calves a low volume of milk during the first few weeks of life to minimize the incidence of neonatal diarrhea. Therefore it is important to evaluate feeding practices to correct factors that may be contributing to nutrient deficiency when attempting to limit dairy calf respiratory disease.

Veal calves are at great risk for respiratory disease because they are often reared in rooms that are filled to a high stocking rate with calves from multiple dairies that may put minimal effort into ensuring that the calves are fed adequate amounts of good-quality colostrum. Similar problems can occur on calf-rearing facilities where hundreds to thousands of very young dairy calves are raised until they are old enough to be returned to dairies to become lactating cows or sent on to feedlots. A high proportion of calves that enter calf-rearing facilities may have failure of transfer of passive immunity unless the operation managers uphold standards for passive immunity in calves they receive.

MANAGEMENT PRACTICES TO MINIMIZE PREWEANING BEEF CALF RESPIRATORY DISEASE. Relative to dairy calves, less is known about management practices that should prevent preweaning respiratory disease in beef calves. Risk factors identified include a longer calving season, concurrent neonatal calf diarrhea, and practices that increase opportunities for introduction of respiratory pathogens to the herd or that increase opportunities for close contact among calves and between cows, older calves, and younger calves. Thus in herds where preweaning calf respiratory disease is a problem, it may be helpful to decrease or prevent situations where preweaning calves and/or cows are brought together in close proximity. Improving immunity of preweaning calves by addressing factors that can lead to failure of transfer of immunity from colostrum (such as dystocia and hypothermia) may help mitigate prewean­ing calf respiratory disease, particularly in herds with a high incidence of respiratory disease in calves in the first month or two of life, when maternal antibodies should be most protective. Because occurrence of calf diarrhea has been associated with preweaning calf respiratory disease, efforts to control calf diarrhea, which usually precedes respiratory disease, should be undertaken in herds with both problems.

Administration of vaccines for viral and bacterial respiratory pathogens to preweaning beef calves may help decrease respira­tory disease. Anecdotally, cow-calf operations with a history of perennial outbreaks of preweaning calf respiratory disease have reported decreased rates of disease when respiratory vaccines are administered to calves prior to the time that outbreaks are expected. Vaccination of beef calves still nursing their dams can be logistically challenging and may not have a favorable cost-to-benefit ratio on all farms.

Once an outbreak is underway, anecdotal reports suggest that vaccination with intranasal or injectable modified live vaccines containing IBRV, PIV-3, and/or BRSV may be helpful to shorten the outbreak, but this is not yet confirmed by controlled research. Moreover, BRSV vaccination in the face of a BRSV outbreak has been associated with apparent disease enhancement,⁹⁴ thus it is possible that administration of BRSV vacccine could make an outbreak of undifferentiated calf respiratory disease worse if BRSV is the cause of the outbreak.

Vaccination to prevent bovine respiratory disease is discussed in detail in Chapter 48.

MANAGEMENT PRACTICES TO MINIMIZE FEEDLOT AND STOCKER RESPIRATORY DISEASE

Preconditioning. Preconditioning of calves is a practice undertaken to limit the impact of risk factors that influence the occurrence of BRD in feedlot cattle. Preconditioned calves are weaned well in advance of shipment to feedlots. They are trained to eat some grain from feed bunks and drink water from tanks; this is especially important for calves raised on rangeland where feed bunks or water tank may not be seen. Calves are castrated and dehorned, treated for internal and external parasites, and vaccinated against respiratory pathogens, with priming and booster vaccine administration timed to allow a full response to vaccination before calves are shipped to the feedlot. The exact details of a preconditioning program can be tailored to the needs and characteristics of the individual herd of cattle. A variety of preconditioning protocols have been described, and most of the major companies that sell vaccines have recommended standardized preconditioning programs. Also, in many areas of the United States and Canada, state, provincial, or regional groups may offer a standardized preconditioning program for local cattle producers.

The value of preconditioning has been debated over decades. A summary of eight studies comparing the health of precon­ditioned calves with that of control calves indicated that, on average, preconditioning reduced the morbidity rate by 23% and the mortality rate by 50% in the feedlot.⁹⁵ However, preconditioned cattle do not always escape disease once they enter feedlots, and they sometimes experience outbreaks of high morbidity and mortality not unlike those seen in high-risk calves that are not preconditioned. Moreover, even when preconditioned calves experience less disease, their performance in the feedlot is not always better than that of nonpreconditioned calves,⁹⁶ or they may not always perform well enough that a profit that is greater than the cost of preconditioning is returned.⁹⁷ An evaluation of data collected over 8 years by the Texas A&M Ranch to Rail program showed that preconditioned cattle returned on average $90 more per head than nonprec­onditioned cattle. However, in some years the return was better for preconditioned cattle than in other years. These data emphasize that preconditioning is likely to be cost-effective in the long run, but it may not always be cost-effective for an individual group of cattle in a single year. Also, while cattle that develop BRD in the feedlot often have decreased weight gain and/or feed efficiency and reduced carcass quality at slaughter,^64-66 they sometimes exhibit compensatory gain after they recover from BRD, which allows them to “catch up” to cattle that do not develop BRD.⁶⁷ For this reason, some feedlot operators elect not to specifically purchase preconditioned cattle, which can cost more to purchase and may not consistently yield higher profits. Because of year-to-year uncertainty in the economic advantage of preconditioned cattle, producers who sell preconditioned calves may not always be able to sell calves at a price that provides a profit over the cost of preconditioning. If an individual producer or producer organization develops a good reputation for generating reliably healthy preconditioned calves, marketing these calves directly to cattle buyers may be the best way for the producer to realize a profit from precon­ditioned calves. Retaining ownership of calves sent to feedlots may also allow the producer to realize better profits, but this requires a relationship with a feedlot that will manage the calves in ways that will continue to optimize health once the calves enter the feedlot. It has also been shown that precon­ditioning can help the producer net greater returns simply because preconditioned calves weigh more when they are sold.⁹⁸

Backgrounding. Another practice similar to precondition­ing is the practice of backgrounding. In backgrounding, weaned beef calves from a variety of sources (often purchased from multiple sale barns) are accumulated and processed in a manner similar to that carried out for high-risk calves at feedlot entry. Calves are then sorted by size and type and sold to feedlots, usually within a few days of arriving at the backgrounding operations. Backgrounding operations are sometimes referred to as “conditioning” operations. A variation of the background­ing operation is the stocker operation; in stocker operations calves are processed and then “stocked” onto pastures, often with supplemental concentrate feeding, to graze and grow for a few weeks to months before shipment to feedlots. The difference between preconditioning and backgrounding is that preconditioning occurs on the farm where the calf is born or at least before the calf is mixed with other calves from different sources, with some aspects of treatment such as the first dose of vaccines ideally being administered before weaning. Calves that enter backgrounding or stocker operations often have uncertain health histories, they often have been weaned immediately before purchase, and when they arrive they have been mixed with calves with similar uncertain backgrounds from a variety of sources. Because of this, disease outbreaks of high morbidity and mortality are not uncommon on backgrounding and stocker operations, and respiratory disease is the leading cause of morbidity and mortality.⁸⁹ The backgrounding or stocker operator is thus taking on some of the risk of high- risk calves and is theoretically providing the feedlot with animals more likely to grow well with minimal disease than if the cattle entered the feedlot straight from the auction market.

Management at Feedlot Entry. It is not surprising that preconditioning does not always influence the occurrence of respiratory disease in cattle after they enter the feedlot because it has no effect on many risk factors active during transit and in the feedlot. Therefore optimal control of feedlot respiratory disease should begin with preconditioning and continue with avoidance of auction yards, minimization of transport time to the feedlot, limited mixing of calves from different sources, limited number of calves per pen, and careful diet management in the feedlot. Correction of vitamin and/or mineral deficiencies if known or detected, using vitamin injections in entering calves, may be helpful to decrease disease associated with immuno­deficiencies of nutritional origin.

Processing procedures on arrival at the feedlot can affect the incidence of BRD. General recommendations for handling incoming cattle (the “receiving program”) that are appropriate for any category of animals can be made.^26,89,99 In a receiving program, rest, rehydration, and ruminal restoration need to be addressed because cattle are physically and psychologically stressed by the marketing and transportation processes. It is recommended that these cattle be rested for 12 to 24 hours and that in the summer they be processed before the hottest part of the day. Prolonged holding before processing is associ­ated with increased illness, and holding times over 48 hours should be avoided. Holding pens should be clean and dry or have dry bedding because this allows all cattle to lie down and rest. Shelter from wind, sun, rain, and dust should also be provided in the receiving pen.

It is important that incoming cattle have access to clean, fresh water. Raised spigots have been suggested as a way to teach incoming cattle to drink out of automatic watering devices because cattle that may not be familiar with water tanks will be attracted to the sound of splashing water. Incoming cattle should also be offered good-quality, long-stem grass hay on arrival. Hay is the best foodstuff for restoring or refilling the rumen. Hay can be put in the feed bunks as well as in feeders in the pen as a way of teaching cattle to eat out of bunks. Hay feeders may also be put along the pen perimeter to decrease walking the fence line and encourage eating. The starter ration is an important source of energy and should be highly palatable. The proportion of the starter ration dry matter that is forage is not usually less than 50% to prevent problems of acidosis. Starter rations often contain a coccidiostat because coccidiosis can occur in calves after commingling.

Processing protocols may be tailored to the category of the incoming cattle. Pharmaceutical processing options can include vaccination (respiratory and other), vitamin injections, growth hormone implanting, treatment for internal and external parasites, long-acting antibiotic therapy, drugs for aborting pregnant heifers, and probiotic administration. Management procedures for processing include ear tagging, branding, tail trimming, castration, and tip dehorning. Some management procedures such as castration and dehorning could be left for a later time—for example, at reimplanting at 70 to 90 days on feed (if cattle are expected to be on feed for more than 150 days). Taking the rectal temperature of cattle at initial processing may be helpful in identifying sick cattle.

Although vaccination of cattle to prevent respiratory disease when they are first received by feedlot or backgrounding and stocker operations is a common practice, research has not found the practice to be consistently associated with decreased BRD risk.^83,100 In a recent study, delayed administration of multivalent modified live viral respiratory vaccine, in contrast to administration at arrival, was associated with a decreased rate of second treatment for BRD.³⁸ Failure of vaccination at arrival to protect cattle against later respiratory disease may be because cattle are already infected at the time of vaccination

■ BOX 31.6

Examples of Processing Protocols for High-Risk and Low-Risk Cattle Entering Feedlots

Processing Protocol for High-Risk Cattle: Recently Weaned Cattle Purchased Through Auction Markets

1. Modified live BHV-1 (IBRV), BVDV1, BVDV2, BRSV, and PIV-3 vaccines^a

2. Eight-way clostridial bacterin^a

3. Antiparasitic

4. Mannheimia haemolytica ± Pasteurella multocida vaccine

5. Histophilus somni vaccine (if significant problem in past)

6. Growth implant

7. Ear tag identification

8. Bulls castrated (if needed)

9. Tip dehorning (if needed)

10. Metaphylactic antimicrobial treatment

Processing Protocol for Low-Risk Cattle: Healthy Yearlings Previously Fed in Backgrounding Operations

1. Modified live BHV-1 (IBRV), BVDV1, BVDV2, BRSV, and PIV-3 vaccines

2. Eight-way clostridial vaccine

3. Antiparasitic

4. Growth implant

5. Ear tag identification

^aExperts are currently debating whether vaccines should be given to high-risk cattle at arrival or be delayed for some time.

BHV-1, Bovine herpesvirus type 1; BRSV, bovine respiratory syncytial virus; BVDV, bovine viral diarrhea virus; IBRV, infectious bovine rhinotracheitis virus; PIV-3, bovine parainfluenza virus type 3

because they are not capable of mounting an adequately protec­tive immune response in time, or because disease is caused by agents not included in the vaccines that are administered. Following on-arrival vaccination, cattle are sometimes given a second dose of respiratory vaccine 7 to 21 days after the initial dose at feedlot entry; it is not clear whether this is consistently beneficial. See examples of processing protocols for high-risk and low-risk cattle in Box 31.6.

Metaphylactic Antimicrobial Therapy. The term metaphylaxis refers to the administration of an antimicrobial to a group of animals that may be in the early stages of bacterial pneumonia or that are at significant risk of developing bacterial pneumonia. Thus the antimicrobial drug administered may have either therapeutic or prophylactic effect, depending on the state of each animal treated. Metaphylactic administration of antibiotics on arrival has been shown in many studies to decrease morbidity and mortality in groups of high-risk cattle.^101,102 Long-acting antibiotics have been reported to significantly alter the number of calves from which M. haemolytica can be cultured.^103,104 An additional rationale for metaphylaxis on arrival is based on the epidemic curve of fatal disease onset for bacterial bronchopneumonia, which shows that feedlot calves dying from fatal fibrinous pneumonia are already sick on arrival or become ill within days of arrival. Although metaphylaxis through feed and water was used in the past, it is currently recommended that metaphylaxis be administered by use of injectable antimicrobial agents. The ability of these drugs to reach therapeutic levels quickly in all animals gives them a clear advantage given the previously discussed rationale for bacterial bronchopneumonia metaphylaxis.

A number of trials that examine various antimicrobial agents and their effectiveness for bacterial bronchopneumonia metaphylaxis have been published. Most of these studies have examined both health and production values, and a variety of products have been shown to be efficacious in decreasing respiratory morbidity and mortality and sometimes in improv­ing production parameters. Recent meta-analyses provide estimates of the relative efficacy of many of the antimicrobials currently labeled for treatment or control of bovine respiratory disease.^23-25 At the time of this writing, several antimicrobials are approved for administration to control BRD (metaphylaxis; see Table 31.15).

Similar use of long-acting antimicrobials in dairy calves may also be of value. The disease process does not have the same narrow windows of therapeutic intervention that occur in calves entering the feedlot. Dairy calves properly managed in maternity facilities and raised in hutches rarely experience any respiratory disease until they are moved to postweaning housing. Injectable mass medication is often used at the time calves are moved as a means of controlling postweaning BRD.⁵²

Although metaphylactic antimicrobial administration has clearly been effective in decreasing BRD morbidity in high-risk beef cattle, recent reports have described a high prevalence of M. haemolytica resistant to multiple classes of antimicrobials on nasopharyngeal swabs collected from stocker cattle after metaphylactic antimicrobial administration.¹⁰⁵ The degree to which MDR M. haemolytica negatively affect outcome in cattle colonized by these bacteria is not yet clear, but dissemination of MDR M. haemolytica in cattle populations may begin to decrease the benefit of metaphylaxis.

MANAGEMENT PRACTICES FOR PREVENTING RESPIRATORY DISEASE IN SHEEP AND GOATS. Prevention of pneumonia in sheep and goats is also based on altering the risk factors that predispose to pneumonia. Minimizing cold and heat stress, providing properly ventilated housing, avoiding overcrowding, and avoiding long transport in adverse weather aid in prevention. Mass medication can be used to control outbreaks of pneumonia in flocks. Injectable long-acting oxytetracycline is often used; tilmicosin can also be used for mass medication therapy for sheep, but it should never be administered to goats, as it can result in fatal reactions. Feedlot lambs are sometimes admin­istered metaphylactic therapy (long-acting oxytetracycline) on arrival. See Table 31.15 for a list of antimicrobials approved for adminstration to sheep and goats.