Incidence and heritability of ovine pneumonia, and the relationship with production traits in New Zealand sheep

The cost of ovine pneumonia and pleurisy to the New Zealand economy is high, with the majority of loss through slower growth and reduced carcass value at slaughter. Farm management practices and vaccine development have traditionally been the main focus for prevention of pneumonia. The objective of this study was to estimate the heritability of pneumonia in New Zealand lambs, and investigate the genetic relationship with key production traits. The lungs of 11,437 lambs from pedigree-recorded flocks were scored for the presence and severity of pneumonic lesions at slaughter. On average 28% of lambs had pneumonic lesions at slaughter, with 7% showing severe lesions. The incidence of pleurisy in these animals was 6%. Heritability estimates for pneumonic lesions and pleurisy were 0.07 ± 0.02 and 0.02 ± 0.01, respectively. There was a significant positive genetic correlation between pneumonic lesions and faecal egg count (0.30 ± 0.13). Animals with pneumonic lesions had grown faster from birth to weaning, and slower from weaning to slaughter than animals without lesions. This study has shown that there is a heritable component to pneumonia in sheep. Including more data from pedigree-recorded flocks with severe pneumonia and a high incidence of pleurisy will enable more accurate estimates of genetic parameters, and subsequent correlations with production and disease traits. This would be aided by routine recording of pneumonia in lungs at slaughter by processing plants.