Pneumonic lesions in lambs in New Zealand: patterns of prevalence and effects on production

Abstract

AIM: To describe temporal and spatial patterns of the prevalence of pneumonia in lambs in three regions of New Zealand, and determine effects on liveweight gain.

METHODS: A longitudinal study was conducted in 1999–2000 on 14 commercial sheep farms, five from the Southland region of the South Island, and five from the King Country and four from the Northland regions of the North Island. Pneumonia was known to be a problem in lambs on all farms selected. On each farm, 400 lambs were randomly selected at weaning and allocated at random to one of two groups (Groups I and II). Lambs in both groups were weighed at 4-weekly intervals. The extent of pneumonic lesions in lungs was scored visually at slaughter in 40 randomly selected lambs after each weighing (Group I). Lambs in Group II were selected for slaughter by the farm manager on a commercial basis of liveweight and body condition, then assessed for pneumonic lesions.

RESULTS: Prevalence of extensive pneumonic lesions (≥10% lung surface area affected) increased from December to March from 1.4 to 10.1% lambs in Southland (n=1,917),1.2 to 25.7% in the King Country (n=1,831), and 4.7 to 21.4% in Northland (n=1,485). Overall, 42.3% of lambs in both groups had pneu- monic lesions (n=5,233) and in 15.1% of these, ≥5% of the lung surface area was affected. Daily weight gain in the month prior to slaughter was reduced in lambs for which ≥20% lung surface area was affected in Group I (p<0.05) but not in Group II.

CONCLUSIONS: The association between pneumonic lesions and reduced weight gain was highly significant in lambs from Group I, but not from Group II. Thus, pneumonia had a negative impact on weight gain, and selection by farmers of lambs for slaughter counteracted this association in lambs from Group II.

CLINICAL RELEVANCE: Pneumonia occurs commonly as a subdinical disease in lambs in New Zealand. It has no public health significance and is not recorded at slaughter plants nor reported to farmer clients. Effects of the disease on daily weight gain of lambs is considerable and costly for lamb producers.

KEY WORDS:

• Pneumonia
• prevalence
• spatial and temporal patterns
• longitudinal study
• commercial sheep farms
• slaughter
• pneumonic lesions
• commercial selection criteria
• lung surface area
• daily weight gain
• subclinical

Acknowledgements

The authors wish to thank the farmers involved in the study, the workers and meat inspectors at the processing plants, and the people who helped with the labour-intensive data collection. This research was funded by Meat New Zealand.