Genetic resistance to experimental infection with Mycobacterium bovis in red deer (Cervus elaphus)

Tuberculosis (Tb) caused by Mycobacterium bovis is a worldwide threat to li vestock and humans. One control strategy is to breed livestock that are mor e resistant to Mycobacterium bovis, In a 3-year heritability study 6 farmed red deer stags were selected from 39 on the basis of their differing respo nses to experimental challenge via the tonsillar sac with approximately 500 CFU of M. bovis, Two stags remained uninfected, two were moderately affect ed, and two developed serious spreading Tb, Seventy offspring, bred from th ese six stags by artificial insemination using stared semen, were similarly challenged with M. bovis, The offspring showed patterns of response to M. bovis challenge similar to those of their sires, providing evidence for a s trong genetic basis to resistance to Tb, with an estimated heritability of 0.48 (standard error, 0.096; P < 0.01). This is the first time the heritabi lity of Tb resistance in domestic livestock has been measured. The breeding of selection lines of resistant and susceptible deer will provide an ideal model to study the mechanisms of Tb resistance in a ruminant and could pro vide an additional strategy for reducing the number and severity of outbrea ks of Tb in farmed deer herds. Laboratory studies to identify genetic and i mmunological markers for resistance to Tb are under way. Preliminary studie s showed no associations between NRAMP or DRB genes and resistance to Tb in deer, Patterns of immune responses seen in resistant animals suggest that both innate and acquired pathways of immunity are necessary to produce the resistant phenotype.