Heritability of resistance to bacterial infection in meat rabbits
Incidence of visual signs of bacterial infection and mortality, from causes related to bacterial infection, were recorded on a weekly basis in growing meat rabbits from 5 to 10 weeks of age. Heritability of Weekly Incidence of disease was highest in weeks 9 and 10 (0.05 ± 0.02 and 0.06 ± 0.02, respectively with linear model, and 0.10 ± 0.06 and 0.12 ± 0.05, respectively with a threshold model). Common litter effects accounted for 5–20% of the variance of disease incidence, while maternal genetic variance was small (0–3%). Individuals from small litters at weaning had higher disease incidence, and disease incidence reduced as litter parity of the doe increased (P < 0.05), when the disease trait was measured at week 9 and 10, but not for earlier weeks. Genetic correlations between disease incidence and mortality were imprecise and not different from zero. Phenotypic correlations were low to moderate, and positive. Although the mechanism at this stage is unknown, these findings suggest that there are common/shared immunological responses to bacterial challenge that are under genetic control. This study demonstrates that observed signs of bacterial infection in rabbits can be used as an indicator trait for resistance to bacterial infection, and the heritability of the trait is high enough to warrant further evaluation of the merit of including it in a breeding program. From one week to the next, rabbits exhibiting disease symptoms were more likely (10 to 50 times depending on week of measurement) to die than those that were healthy. The relative economic value of resistance to bacterial infection could be based on the relationship between disease incidence and survival, as well as the direct costs of effective disease control and treatment.