Preliminary analysis of immune competence traits in northern Australian tropically adapted beef breeds

Immune competence traits (cell-mediated and antibody-mediated immune responsiveness) were evaluated in northern Australian tropically-adapted beef breeds. A total of 784 Brahman, Droughtmaster, and Santa Gertrudis steers were recorded at weaning for the two traits. The development of a statistical model showed year of birth and breed were significant (P<0.05) for both immune competence traits. For the cell-mediated immune response, the starting (day 0) live weight and the baseline skin thickness ratio was also significant. Heritability estimates were low to moderate for both traits, with 0.18 and 0.22 for cell-mediated and antibody-mediated immune responses, respectively. These preliminary results indicate that genetic variation exists for these immune competence traits in tropically adapted beef breeds. Further research is required to determine if selecting for immune competence in tropical breeds also improves profit by improving production, health (i.e. reduced reliance on antibiotics to prevent or treat disease) and welfare traits.