Hemophilus somnus Bacterins

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incorporated into preconditioning programs would also be highly desirable. When pasteurella pneumonia is encountered following weaning and/or grouping of dairy calves, a similar approach would also be warranted. The presence of humoral antibodies protects solidly against abortions caused by PI3 virus. In contrast, immunity to respiratory infection with PI3 virus, following either vaccination or natural exposure, is partial rather than complete. Infection and disease may occur in the presence of either passive or active humoral antibodies. 7 Consequently, PI3 vaccines should probably not be depended upon for protection for more than a few months following administration. Passive antibodies may persist in calves until 8 months of age and may interfere with active immunization. Consequently, calves vaccinated prior to 8 months of age should be revaccinated upon reaching 8 or 9 months of age}O PI3 vaccines are not recommended for administration to cattle upon arrival at the feedlot, because this usage is unlikely to be costeffective. l l Serologic surveys indicate that most cattle arriving at the feedlot are probably immune. 7 Most of the remainder will usually have been exposed to PI3 virus during gathering and transportation. REFERENCES 1. Mohanty SB: Bovine respiratory viruses. Adv Vet Sci Comp Med 22:83-109, 1978 2. Reed SE, Boyd A: Organ cultures of respiratory epithelium infected with rhinovirus or para-influenza virus studied in a scanning electron microscope. Infect Immun 6:68-76, 1972 3. Roth JA: Immunosuppression and immunomodulation in bovine respiratory disease. In Loan RW (ed): Bovine Respiratory Disease. College Station, Texas A & M Univ Press, 1984, pp 143-192 4. Lopez A, Thompson RG, Savan M: Pulmonary clearance of P. hemolytica in calves infected with bovine PI3 virus. Can J Comp Med 40:385-391, 1976 5. Frank GH, Smith PC: Prevalence of Pasteurella hemolytica in transported calves. Am J Vet Res 44:981-985,1983 6. Grey CL, Thompson RG: Pasteurella hemolytica in the tracheal air of calves. Can J Comp Med 35:121-128, 1971 7. Kahrs RF: Viral Diseases of Cattle. Ames, Iowa State Univ Press, 1981, pp 1-299 8. Rosenquist BD, Dobson AW: Multiple viral infection in calves with acute bovine respiratory tract disease. Am J Vet Res 35:363-365, 1974 9. Gutekunst DE, Paton 1M, Volenec FJ: Parainfluenza-3 vaccine in cattle: Comparative efficacy of intranasal and intramuscular routes. J Am Vet Med Assoc 155:1879-1885,1969 10. Sweat RL: Epizootiologic studies of bovine myxovirus parainfluenza-3. J Am Vet Med Assoc 150:178-183, 1967 11. Woods GT, Mansfield ME, Webb RJ: A three-year comparison of acute respiratory disease, shrink, and weight gain in preconditioned and non-conditioned Illinois beef calves sold at the same auction and mixed in a feedlot. Can J Comp Med 37:249-255, 1973

Hemophilus somnus Bacterins Hemophilus somnus infections can cause (1) thromboembolic meningoencephalitis (TEME), (2) fibrinous pleuritis and pleuropneumonia in feedlot cattle, l (3) bronchopneumonia and fibrinous pneumonia,2 (4) endometritis, (5) abortions, and (6) mastitis.

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H. somnus is one type of upper respiratory bacterial flora of normal cattle. 3 H. somnus-related respiratory or central nervous system (CNS) disease is not thought to occur in the absence of stress. H. somnus is also a normal saprophyte in the prepuce of bulls 4 and in the vaginal mucus of cows. s Vaccination with H. somnus bacterins protected susceptible cattle from intravenous or intracisternal challenge6 or from intratracheal inoculation7 with live, virulent H. somnus organisms. However, to date, no field trial has unequivocally demonstrated that cattle can be protected from natural exposure to H. somnus infections by vaccination.7-17 The absence of definitive field trials is attributed to the sporadic nature of the clinical syndromes caused by H. somnus rather than to any lack of vaccinal efficacy. H. somnus

VACCINATION PROGRAMS

Recommendations for use of H. somnus bacterins are summarized (see Table 5). Two doses should be administered7 by intramuscular or subcutaneous injection, 3 weeks apart, beginning at 4 months of age. Booster doses should be administered annually. H. somnus vaccination is not usually recommended for use in feedlot cattle because H. somnus infections can be more cost-effectively controlled by feed medication than by vaccination. 18 Because of the sporadic nature of H. somnus - related respiratory and CNS infections, the recommendation for feedlots is to diagnose and treat H. somnus infections in individual animals, until the second case in a particular group (pen) is recognized. Then the entire pen is medicated for 10 days with chlortetracycline or oxytetracycline in the feed, using a daily dose of 1 mg per pound of body weight. New cases cease by the third day of medication and seldom recur following termination of therapy. 2 In a recent vaccination field trial in Canadian feedlot cattle, the authors concluded that 17.4% of fatal respiratory disease in unvaccinated steers could have been prevented by vaccination with an H. somnus bacterin.17 This represented a potential reduction of 0.46% in the overall mortality rate from vaccination. If H. somnus were found to be as important a factor in the respiratory disease problems of other feedlots, as it apparently was in the one studied, routine vaccination would undoubtedly be cost-effective. Most investigators have estimated that H. somnus is involved in the cause of only 1 to 5% of feedlot pneumonia cases. 1.2 The fact that H. somnus vaccination in this study did not reduce the mortality rate from respiratory disease in heifers creates doubt as to the general applicability of the results obtained in steers.17 Vaccination for H. somnus might sometimes be cost effective in preweaning vaccination programs for beef calves and in preconditioning programs for beef cattle that will continue to be grazed. This is because, in contrast to the situation in the feedlot, H. somnus infections in cattle on pasture are unlikely to be promptly and correctly diag-

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nosed, and feed medication on pasture is usually impractical. Outbreaks of H. somnus - caused respiratory or eNS infections in cattle on pasture could be terminated by administration of repository oxytetracycline (LA 200, Pfizer, New York, NY 10017), but only with considerable labor input and expense for drugs. Vaccination of dairy cows with H. somnus bacterins does not appear to have any appreciable effect on the prevalence of endometritis caused by H. somnus and cannot be recommended. Inclusion of H. somnus bacterins in a vaccination program for control of infectious abortion in beef or dairy cows would probably not be cost-effective: H. somnus appears to be an uncommon cause of bovine abortions. The veterinary literature contains only three reports of naturally occurring abortions caused by H. somnus. 19 - 22 Since vaccination of cows against H. somnus has little influence on the prevalence of H. somnus infections of the genital tract in the nonpregnant cow, it is unlikely that vaccination would protect the fetus from ascending H. somnus infections, which could reach the fetus without passing through the maternal blood supply. Since successful prevention of naturally occurring H. somnus abortions by vaccination has not been reported and since the usual route by which the bovine fetus is naturally infected with H. somnus has not been determined, it is presently not possible to have an informed opinion concerning the potential efficacy of H. somnus bacterins in this regard.

REFERENCES 1. Hjerpe CA: The bovine respiratory disease complex. In Howard JL (ed): Current Veterinary Therapy-Food Animal Practice 2. Philadelphia, WB Saunders, 1986, pp 670-681 2. Hjerpe CA: Clinical management of respiratory disease in feedlot cattle. Vet Clin North Am [Large Anim Pract] 5:119-142, 1983 3. Corstvet HE, Panciera RJ, Rinker HB, et al: Survey of tracheas of feedlot cattle for Hemophilus somnus and other selected bacteria. J Am Vet Med Assoc 163:870873, 1973 4. Humphrey JD, Little PB, Barunum DA, et al: Occurrence of Hemophilus somnus in bovine semen and the sheath of bulls and steers. Can J Comp Med 46:215-217, 1982 5. Waldhalm DG, Hall RF, Meinershagen WA, et al: Haemophilus somnus infection in the cow as a possible contributing factor to weak calf syndrome: Isolation and animal inoculation studies. Am J Vet Res 35:1401-1403, 1974 6. Williams JM, Smith GL, Murdock FM: Immunogenicity of a Hemophilus somnus bacterin in cattle. Am J Vet Res 39:1756-1762, 1978 7. Groom SC, Little PB: Effects of vaccination of calves against induced Haemophilus somnus pneumonia. Am J Vet Res 49:793-800, 1988 8. Hall RF, Williams JM: Field evaluation of Haemophilus somnus bacterin. Vet Med/ SAC 72:1368-1370, 1977 9. Saunders JR, Janzen ED: Haemophilus somnus infections II. A Canadian field trial of a commercial bacterin: Clinical and serological results. Can Vet J 21:219-224, 1980 10. Martin SW, Meek AH, Davis DG, et al: Factors associated with mortality in feedlot cattle: The Bruce County beef cattle project. Can J Comp Med 44: 1-10, 1980 11. Martin SW, Meek AH, Davis DG, et al: Factors associated with morbidity and

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12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

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mortality in feedlot calves: The Bruce County beef project, year two. Can J Comp Med 45:103-112, 1981 Martin SW, Meek AH, Davis DG, et al: Factors associated with mortality and treatment costs in feedlot calves: The Bruce County beef project, years 1978, 1979, 1980. Can J Comp Med 46:341-349,1980 Amstutz HE, Horstman LA, Morter RL: Clinical evaluation of the efficacy of Haemophilus somnus and Pasteu.rella spp bacterins. Bov Pract 16:106-108, 1981 Morter RL, Amstutz HE, Crandell RA: Clinical evaluation of prophylactic regimens for bovine respiratory disease. Bov Pract 17:56-58, 1982 Morter RL, Amstutz HE: Evaluating the efficacy of a Haemophilus somnus bacterin in a controlled field trial. Bov Pract 18:82-83, 1983 Martin SW, Janzen ED, Willson P, et al: A field trial of pre shipment vaccination of calves. Can Vet J 25:145-147,1984 Ribble CS, Jim GK, Janzen ED: Efficacy of immunization of feedlot calves with a commercial Haemophilus somnus vaccine. Can J Vet Res 52:191-198, 1988 Davidson IN, Carpenter TE, Hjerpe CA: An example of an economic decision analysis approach to the problem of thromboembolic meningoencephalitis (TEME) in feedlot cattle. Cornell Vet 71:383-390, 1981 Miller RB, Lein DH, McEntee KE, et al: Haemophilus somnus infection of the reproductive tract: A review. J Am Vet Med Assoc 182:1390-1392, 1983 Chladek DW: Bovine abortion associated with Haemophilus somnus. Am J Vet Res 36:1041, 1975 Van Dreumel AA, Kierstead M: Abortion associated with Hemophilus somnus infection in a bovine fetus. Can Vet J 16:367 -370, 1975 Klavano GG: Observations of Hemophilus somnus infection as an agent producing reproductive diseases: Infertility and abortions. In Proc Ann Mtg Soc Theriogenol. pp 139-149, 1980

Pasteurella hemolytica Vaccines P. hemolytica, biotype A, serotype 1 and/or P. multocida infections of the lung are chiefly responsible for the clinical signs and pathologic lesions of bovine bronchopneumonia and fibrinous pneumonia. The etiology and pathogenesis of bronchopneumonia and fibrinous pneumonia are briefly discussed in the section concerning PI3 virus vaccines. P. hemolytica and P. multocida also cause endometritis, metritis, and occasionally septicemia, with or without accompanying bronchopneumonia and fibrinous pneumonia.

General Considerations Conventional formalin-inactivated, whole-cell, aluminum hydroxide - adsorbed P. hemolytica and P. multocida bacterins have been utilized for more than a half-century. In general, they have been found to be ineffective immunizing agents.1 During the past 5 years, a total of six new P. hemolytica vaccines have been introduced in the United States. Four of these new P. hemolytica vaccines utilize modified-live bacterial agents. The two new inactivated P. hemolytica products are subunit vaccines (see Table 5). The immune mechanisms involved in resistance of the bovine lung to P. hemolytica infections are incompletely understood. It is clear, however, that resistance is greatly enhanced by the presence of serum and bronchoalveolar antibodies to (1) the leukotoxin of P. hemolytica