17 July 2012

10 minute read

Introduction

There are vast amounts of information on feedlot health, production, and performance. Interpreting and organizing the information can be challenging for producers, nutritionist, and veterinarians. This proceeding will attempt to draft and organize a list that, inevitably, can be challenged and disputed. Nevertheless, here’s a list generated by a lone veterinary diagnostic pathologist who spends most of his time “carving up dead livestock and chasing bugs.”

1. Water
2. Nutrition
3. The environment and cattle comfort
4. Vaccination and Immunity
5. Antibiotics and Treatment protocols
6. Internal and External parasites
7. Ionophores
8. Growth-promoting Implants
9. Genetics
10. Marketing
11. BVDV exposure

The first three (water, nutrition and cattle comfort) are essential for health and production thoughout all livestock production systems. In regards to water, it appears logical, and appropriate, to monitor water consumption. Yet, few producers know how much water their cattle are consuming. In other livestock production facilies (swine and poultry), an unexpected decrease in water consumption typically preceeds a health event.

Success of the remaining items on the list depend heavily on the first three. A successful vaccination and treatment program is dependent on cattle that are hydrated, in a positive energy balance and are reasonably comfortable. Realizing value from ionophores, implants and genetics can have an additive effect across the list. Although all topics are important, this proceeding will review data on the infectious disease of feedlot cattle, briefly review antibiotics and vaccination considerations.

Bovine Respiratory Disease

Bovine Respiratory Disease Complex (BRDC) continues to be the most significant and challenging feedlot health problem throughout North America. Respiratory disease is the most significant cause of morbidity (70-80%) and mortality (40-50%) in US feedlots. BRDC negatively impacts feedlot health, carcass quality and performance (Smith, 1998). The cause of respiratory disease is multifactoral and complex, but often includes the combination of stressors and exposure to infectious pathogens that compromise immunity and natural defense mechanism that allow for commensal “normal” bacteria of the nose and upper respiratory tract to reach the lung causing disease.

Bacterial pathogens

This proceeding will briefly review Mannheimia hemolytica, Pasteurella multocida, and Histophilus somni. Mycoplasma bovis is an important pathogen in BRDC, but has a complex role, debated significance, and will not be covered. Although these pathogens are reviewed individually, many cases of BRDC have multiple pathogen involvement.

Mannheimia hemolytica, formally known as Pasteurella haemolytica, is a normal commensal of the upper respiratory tract of healthy cattle. Mannheimia hemolytica has many virulence factors that include a leukotoxin responsible for premature death of white blood cells and platelets (Gioia et al., 2006). Commerically available vaccines are designed to stimulate immunity against and bind the leukotoxin. Cattle with Mannheimia hemolytica pulmonary infections are often very ill with high fevers (“Shipping fever”). The leukotoxin produced by the bacteria initiates a cascade of inflammatory events that results in the accumulation of pleura (chest) fluid, fibrinous pleuritis (inflammation of the lung lining), and pulmonary necrosis (lung death). The disease can have a rapid onset and can result in high morbidity, high mortalities, and permanent lung damage.

Pasteurella multocida, like Mannheimia hemolytica, is a gram negative bacteria and normal commensal of the upper respiratory tract. As of now, there are no known significant toxins produced by Pasteurella multocida. Clinical disease is less severe when compared to Mannheimia hemolytica and cattle have increased respiratory rate, fevers, with productive coughing. Co-infections with other bacteria and viruses are common.

Histophilus somni (formerly Haemophilus somnus) is also a gram negative bacteria and a normal commensual of the upper respiratory tract. Histophilus somni has virulence factors that affect the lining of small blood vessels (endothelial cells) allowing the bacteria to reach the bloodsteam and travel to other locations including the heart, brain, and joints. Histophilus somni infection of the brain results in “brainers” that looks similar to, and often confused with, cattle with polioencephalomalacia (“Polio’). Histophilus somni infection of the heart is a common finding in sudden deaths and the bacteria can be found in the joints of lame cattle with arthritis and swollen joints.

Prevalence of Bacterial Pathogens

Bovine lung isolates cultured at the Minnesota Veterinary Diagnostic Laboratory were compiled from 2006 through 2011. During the five year period, Pasteurella multocida was isolated 664 times (46% of total), Mannheimia hemolytica was isolated 428 times (30%), Histophilus somni was isolated 309 times (21%), and Bibersteinia (Pasteurella) trehalosi was isolated 41 times (3%). Multiple bacteria may have been isolated from the same lung and other bacteria, including Mycoplasma bovis, are not reported.

The data were separated into isolates obtained from dairy and beef cattle and there were slight differences. In dairy cattle, Pasteurella multocida was isolated in 52%, Mannheimia hemolytica was isolated in 36%, and Histophilus somni was isolated in 12% of diseased lung. In beef cattle, Pasteurella multocida was isolated in 43%, Mannheimia hemolytica was isolated in 39%, and Histophilus somni was isolated in 18% of diseased lung.

These data are similar to a published report of 237 cases of fatal feedlot pneumonia in a single Oklahoma feed yard (Fulton et al., 2009). In that study, Pasteurella multocida was isolated in 41%, Mannheimia hemolytica in 42%, and Histophilus somni in 17% of diseased beef feedlot calf lung. Additionally, Mycoplasma sp. was isolated in 71% and Arcanobacterium pyogenes was isolated in 35% of lung.

Antibiotics

Many antimicrobial products are available for the aid in the control and treatment of BRDC. Cost, perceived effectiveness, handling characteristics, ease of administration, dosing frequency, client compliance and producer preference are just a few consideration when selecting an antibiotic. When the lung isolates cultured at the Minnesota Veterinary Diagnostic laboratory are exposed to antibiotics in a laboratory (MIC), they produced the susceptibility report as generated in Figure 1.

Viral Pathogens

Viral pathogens associated with BRDC include Bovine Respiratory Syncytial Virus (BRSV), Infectious Bovine Rhinotracheitis (IBRV), Bovine Viral Diarrhea Virus (BVDV), Parainfluenza 3 (PI3) and Bovine Coronavirus (BoCV). Bovine Coronavirus and BVDV were the top two virused detected in diseased bovine lung in an Oklahoma feedlot study (Fulton et al., 2009). Although not specifically tabulated, those finding are similar to submissions at the Minnesota Veterinary Diagnostic Laboratory (personal observation). BoCV and BVDV will be briefly reviewed.

Bovine Coronavirus infection can result in diarrhea, respiratory disease, or both. In one study of feedlot cattle, BoCV infection was associated with an increased risk for cattle developing BRDC and lung lesions (Lathrup et al., 2000). In that study, cattle shedding BoCV were 1.6 times more likely to require treatment. In another study, cattle vaccinated with modified-live BoCV intranasal vaccine resulted in fewer treatments and mortalities (Plummer et al., 2004). In an Ohio feedlot study, seroconversion was inversely related to average daily gain and seropositive cattle gained 13 lbs. more than seronegative cattle (Hasoksuz et al., 2002). Although vaccination against bovine coronavirus appears appealing, additional research is needed to understand the pathogenesis and immunity of BoCV respiratory disease.

Bovine Viral Diarrhea Virus (BVDV) role in BRDC is multifactoral. Although the name of the virus implies disease characterized by diarrhea, the virus typically has a significant negative impact on the immune system and multiple interactions with BRSV, IBRV, PI3, Mycoplasma bovis and Mannheimia haemolytica have been documented (Ridpath, 2010). Fortunately, BVDV infections appear to slow and stop when persistently infected (PI) cattle are removed from the population. Persistently infected cattle are somewhat rare and typically represent less than 1% of the total population. In large feedlots, there is about 1 PI calf per 500 to 1000 cattle. PI cattle are the source of BVDV infections and these cattle shed high levels of virus in many excreations and secretions. Testing for BVDV PI cattle typically involves collecting an ear notch (skin sample) and submitting to a diagnostic laboratory for testing. As of now, fresh ear notch samples tested by antigen capture ELISA (ACE) is the most robust test for detecting PI cattle (Edmondson et al., 2007). In one large feedlot, exposure of the general population to BVDV PI cattle resulted in negative performance losses of $88.26/animal and increased fatalities (Hessman et al., 2009). Removing PI cattle from the feedlot appears to be a wise investment to optimize health and performance.

Vaccination and Immunity

Vaccination and immunization are not the same. Vaccinating livestock is a task involving the administration of a biological compound (virus or bacteria) that requires proper storage, mixing, and handling, that may or may not result in successful immunization. Successful immunization involves the task of vaccination in a healthy animal, with low cortisol (stress hormone), in a positive energy balance, resulting in an immune response.

When designing a vaccination program, it is critically important to consider the health of the patient. Are the cattle hydrated, eating, calm, and healthy? If not, vaccination may not result in adequate immunization. There are multiple scenarios that can result in a poor vaccinate response. Common causes of a poor vaccine response include vaccinating recently shipped cattle that may be stress, dehydrated, and not eating (negative energy balance). In many cases, a 24-hour period of rehydration, rest, and rumen restoration are more important than immediate vaccination.

Inevitably, some recently weaned calves may not have been vaccinated prior to weaning and shipment. These calves arrive at production units with minimal or no immunity to common viral pathogens. Due to the stress of weaning and shipment, these calves may not respond to an initial vaccination within the first few days of arrival. Administration of a second dose of vaccine with the first 14 days is believe to stimulate the immune system in the sub-group of stressed cattle that failed to respond to the first dose. The second dose is not considered a booster, but a revaccination to capture those that didn’t respond to the first vaccination. The revaccination strategy is new and a few studies have showed a positive impact. In one study, once vaccination was as efficacious and vaccinating twice in the prevention of BRDC in high-risk cattle, but the feed efficiency was improved in the twice vaccinated group (REVAC) during the finishing period (Step et al., 2009).

Summary

Attempting to organize prioritize the factors impact feedlot health is subjective, but important. Many of the cattle health problems are impacted by nutrition and the environment. The benefit of available performance “tools,” such as implants and ionophore, can be significantly impacted by overall health, nutrition, and the environment.

Bovine respiratory disease continues to challenge the feed lot industry. Bacterial respiratory pathogens isolated at the Minnesota Veterinary Diagnostic Laboratory do not appear to have significantly changed in the last five years. Better diagnostic assays has resulted in the discovery and impact of bovine coronavirus and BVDV. Mitigating the effect of these virus is expected to have a positive impact on health and performance.

Vaccination will continue an important tool to control and limit the severity of disease. When vaccinating, it is important to consider the health of the vaccine “patient.” Vaccination will result in better immunization when cattle are hydrated, healthy and eating.

References

Smith RA. Impact of disease on feedlot performance: A review. J Anim Sci 1998; 76(1):272–4.

Gioia J, Qin X, Jiang H, et al. The genome sequence of Mannheimia haemolytica A1: insights into virulence, natural competence and Pasteurellaceae phylogeny. J Bacteriol 2006;188:7257–66.

Corbeil LB. Histophilus somni host-parasite relationships. Anim Health Res Rev 2008; 8(2):151–60.

Fulton R, Blood K, Panciera R, et al. Lung pathology and infectious agents in fatal feedlot pneumonias and relationship with mortality, disease onset, and treatments. J Vet Diagn Invest 2009; 21:464-477.

Lathrup S, Wittum T, Brock K, et al. Association between infection of the respiratory tract attribuatable to bovine coronavirus and health and growth preformance of cattle in feedlots. AJVR 2000; 61:1062-1066.

Plummer P, Rohrbach B, Daugherty R, et al. Effect of intranasal vaccination against bovine enteric coronavirus on the occurrence of respiratory tract disease in a commercial backgrounding feedlot. JAVMA 2004; 225(5): 726-731.

Hasoksuz M, Hoset A, Loerch S, et al. Detection of respiratory and enteric shedding of bovine coronavirus in cattle in an Ohio feelot. JVDI 2002; 14(4): 308-313.

Ridpath J, The Contributions of Infections with Bovine Viral Diarrhea Viruses to Bovine Respiratory Disease. Vet Clin Food Animal (26) 2010: 335-348.

Edmondson M, Givens D, Walz P, et al. Comparison of tests for detection of Bovine Viral Diarrhea Virus in Diagnostic Samples. J Vet Diagn Invest 2007: 376-381.

Hessman B, Fulton R, Sjeklocha D, et al. Evaluation of economic effects and the health and performance of the general cattle population after exposure to cattle persistently infected with bovine viral diarrhea virus in a starter feedlot. AJVR 2009 70(1): 73-85.

Step D, Krehbiel C, Burciaga-Robles L, et al. Comparison of single vaccination versus revaccination with a modified-live virus vaccine containing bovine herpesvirus-1, bovine viral diarrhea virus (types 1a and 2a), parainfluenza type 3 virus, and bovine respiratory syncytial virus in the prevention of bovine respiraotyr disease in cattle. JAVMA 2009 235(5): 580-587.

July 2012