- •Immunoglobulin Function
- •Immunoglobulin Content of Colostrum
- •Immunodeficiency Diseases
- •References
- •Immunologic response to
- •Vaccination by I.K.M. Liu
- •Strangles
- •Immunity and Vaccination in Foals
- •References
- •Skin Testing
- •Anaphylactoid Reactions
- •References
- •Diseases of the teeth and paranasal sinuses by g,j. Baker
- •A.Deciduous
- •Table 4. Sites of Apical Infection in Cheek Teeth
Immunity and Vaccination in Foals
Maternal antibodies passively transferred in colostrum confer excellent immunity to foals. Levels of maternal antibodies decrease through normal catabolic processes until the foal becomes susceptible to diseases indigenous to its relatively new environment. Vaccination should commence at this point. Ideally, the duration of immunity conferred by colostral antibodies should be assessed before initial vaccination against specific diseases in foals. This is particularly important since passively acquired antibodies often interfere with the response to active immunization. However, it is impractical to assess the persistence of passively acquired antibodies in individual foals to determine the optimal time for initial vaccination. The persistence and rate of decline of passively acquired antibodies depends upon the concentration of colostral antibodies absorbed and on the amount of antigenic stimulation during this period. Interference with the response to immunization by passively acquired antibodies is thought to occur with administration of vaccines for strangles, equine viral arteritis, equine encephalomyelitis and African horse sickness.20-23 These studies indicate that the practice of immunizing foals in the first few weeks of life is neither logical nor advantageous unless failure of passive transfer has occurred.
The persistence of maternal antibodies in foals has been investigated.9 Serum-neutralization tests for colostral EHV-1 antibodies in 14 foals showed adequate protection against EHV-1 infection within a few days after birth. Passively derived antibody levels decreased to marginally protective levels by 2 months of age and to nonprotective levels by 3 months of age.
Similar results were obtained in a study of the duration of passive immunity to equine viral arteritis.21 Protective titers present 24 hours after birth steadily declined to marginal or nonprotective levels. By 4 months of age, antibodies against equine viral arteritis were not detectible in 6 of 8 foals; the 2 remaining foals had marginally protective antibody levels.
Recent investigations of antibodies passively acquired from administration of tetanus antitoxin indicated that 60% of foals lost their protective titers by 2 months of age.24 By 3 months of age, 77% lost their protective titers against tetanus. Other investigations on the duration of passive immunity to tetanus in foals revealed protective antibody levels for up to 6 months and up to 12-18 months after administration of tetanus antitoxin.20.25 More studies are needed to clarify these differences.
Results of these studies in foals suggest initiation of vaccination against certain diseases at 2-3 months of age rather than at 4-6 months of age. Evidence supporting this view is that combined-immunodeficient (CID) foals that cannot respond immunologically remain healthy until 2 months of age, providing transfer of passive immunity is complete. At 2 months of age, however, such foals become remarkably susceptible to infection once maternal antibodies are catabolized.
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From the information available, initial vaccination at approximately 3 months of age, followed by revaccination 2-3 months later, offers the best protection up to 7-9 months of age.