The eradication effects of pullorum disease on chicken flocks mortality in 297 large-scale farms in China

Pullorum disease (PD) can cause infection and spread of disease through horizontal propagation between individuals and vertical propagation by hatching eggs to the next generations, regardless of the variety and age, chickens are extremely susceptible to this disease. PD could be prevented, controlled, and eliminated by eradication at both farm and national levels through a strict procedure on positive animals, and healthy animals nurturing. Using sample data from 297 large-scale chicken farms in China during 2011-2015, we recognize the relationship between the eradication effect of PD and chicken flocks mortality based on panel Tobit, fixed effect, and random effect models. By comparing large-scale chicken farms that carrying out eradication of PD or not, we identified how eradication affected chicken flocks mortality. Further, we distinguished the eradication effects of PD on the mortality of chicken flocks with different scales. The results showed that, firstly, eradicating PD could effectively reduce flocks mortality with an average decrease of 0.400% compared with uneradicated farms. Secondly, the farm with a raising-scale ranging from 34,400 to 132,400 chickens exhibits optimal eradication effects. Although we could not extrapolate to all China’s chicken farms, these findings suggest that the mortality would be decreased when carrying out the eradication of PD. Eradicating PD in undersized or oversized chicken farms both probably cause diseconomies of scale.