title: Effect of intranasal exposure to leukotoxin-deficient Mannheimia haemolytica at the time of arrival at the feedyard on subsequent isolation of M haemolytica from nasal secretions of calves.
abstract: OBJECTIVE
  To determine the effect of intranasal exposure to live leukotoxin (LktA)-deficient Mannheimia haemolytica (MH) at the time of feedyard arrival on nasopharyngeal colonization by wild-type MH in calves.
  
  
  METHODS
  200 calves.
  
  
  METHODS
  Calves from Arkansas (AR calves; n = 100; mean body weight, 205 kg) were purchased from an order buyer barn. Calves from New Mexico (NM calves; n = 100; mean body weight, 188 kg) were obtained from a single ranch. Calves were transported to a feedyard, where half of each group was exposed intranasally with LktA-deficient MH at the time of arrival. Calves were observed daily for respiratory tract disease (RTD), and nasal swab specimens were collected periodically to determine nasopharyngeal colonization status with MH. Serum samples were assayed for antibodies to MH.
  
  
  RESULTS
  15 AR calves had nasopharyngeal colonization by wild-type MH at the order buyer barn, whereas none of the NM calves had nasopharyngeal colonization. Intranasal exposure to LktA-deficient MH elicited an increase in serum antibody titers against MH in NM calves, but titers were less in NM calves treated for RTD. Exposure of NM calves to LktA-deficient MH offered protection from nasopharyngeal colonization by wild-type MH.
  
  
  CONCLUSIONS
  Exposure of calves to LktA-deficient MH elicited an increase in serum antibody titers against MH and decreased colonization of the nasopharynx by wild-type MH. Earlier exposure would likely allow an immune response to develop before transportation and offer protection from nasopharyngeal colonization and pneumonia caused by wild-type MH.
authors.affiliation: USDA, Agriculture Research Service, National Animal Disease Center, PO Box 70, Ames, IA 50010, USA.
authors.forename: Glynn H
authors.initials: GH
authors.lastname: Frank
authors.forename: Robert E
authors.initials: RE
authors.lastname: Briggs
authors.forename: Glenn C
authors.initials: GC
authors.lastname: Duff
authors.forename: H Scott
authors.initials: HS
authors.lastname: Hurd
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000276:immunology; D001131:Arkansas; D001428:Bacterial Vaccines / Q000276:immunology; D002417:Cattle; D002418:Cattle Diseases / Q000276:immunology / Q000382:microbiology* / Q000517:prevention & control*; D005098:Exotoxins / Q000378:metabolism*; D016978:Mannheimia haemolytica / Q000276:immunology* / Q000472:pathogenicity* / Q000502:physiology; D009297:Nasal Mucosa / Q000276:immunology / Q000382:microbiology*; D009305:Nasopharynx / Q000276:immunology / Q000382:microbiology; D009516:New Mexico; D016871:Pasteurellaceae Infections / Q000276:immunology / Q000517:prevention & control*; D012141:Respiratory Tract Infections / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control / Q000662:veterinary; D013997:Time Factors; D014611:Vaccination / Q000662:veterinary*
chemical_list: D000907:Antibodies, Bacterial; D001428:Bacterial Vaccines; D005098:Exotoxins; C018579:leukotoxin