The active immune system involves phagocytic, cell mediated and humoral processes plus complement proteins, all interacting to protect the individual from pathogenic organisms. Passive immunity is acquired by new-born ungulates by ingestion of immunoglobulins from colostrum. Research in laboratory animals has established that peak antibody synthesis following challenge with a foreign antigen responds readily to directional selection. The increased titre frequently results in enhanced resistance to some diseases but enhanced susceptibility to others. Oregon State University research has produced conflicting results as to the heritability of the ability of new-born calves and lambs to acquire and absorb colostral immunoglobulins and as to the heritability of this passive immunity considered as a trait of the dam. Significant differences among breeds, selection lines and strains did exist for level of colostral immunoglobulins, and low levels (and, in one experiment, high levels as well) were associated with lower neonatal survival. In cattle, there was little evidence that either active immune response or level of complement protein C3 was heritable; but in ewes, the antibody titre to a challenge antigen was moderately to highly heritable. The authors speculate that stabilising selection for immune system traits might be most effective to improve generalised disease resistance and overall livestock production efficiency.
Proceedings of the New Zealand Society of Animal Production, Volume 45, , 225-228, 1985
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