Lamb rib fractures prelimary investigation

Summary

Rib fractures in lambs is a costly condition that results in a significant economic loss estimated to be $3 million per annum to producers and processors and raises significant welfare concerns. Incidence in lambs has been reported by some processors for decades but it was not until the introduction of the Enhanced Abattoir Surveillance (EAS) program by The Department of Primary Industries and Regions of South Australia (PIRSA) in 2007 that its true prevalence was established.
Whilst previously considered a consequence of primary trauma due to poor husbandry it is now postulated that these fractures are secondary to pathologically weakened bones. With a greater understanding of neonatal and juvenile animal bone pathology the cause of these fractures may be identified and potentially eliminated.
The objective of this study was to investigate possible predisposing factors on-farm leading to rib fractures diagnosed in lambs at slaughter, concentrating on the potential role of copper (Cu) deficiency. Using the EAS data 37 properties with and without rib frcature histories were enrolled from the south east of South Australia and Kangaroo Island in a study to examine the mineral content of pasture as well as the liver and bones of stillborn and mismothered lambs. A copper supplementation trial was also conducted on a property with a history of rib fracture tracebacks from the abattoirs.
Lambs lower in liver copper had a greater bone density (p<0.05). there was no difference in bone density or cortical thickness between those properties with or without a history of rib fractures. there were associations between pasture mineral content and  properties with a history of rib fracture incidence, but this was not evident in liver samples from the same properties. liver mineral status in neonatal lambs had no bearing on the presence or absence of rib fractures. in addition, the copper supplementation trial had no impact on the prevalence of rib fractures.>
Although areas in South Australia with the highest incidence of rib fractures are often also recognised as copper deficient areas, there did not appear to be a direct association between copper deficiency and predisposition to bone fractures based on this preliminary study.
An investigation at the individual animal level may produce more definitive results. Ideally, collecting results at slaughter and assessing the mineral status and bone strength of individual animals may give a greater correlation between nutritional status and bone health.
While seasonal conditions were exceptionally dry this year, the combination of the on-property survey and the supplementation trial does discount the hypothesis that rib fractures are primarily a copper responsive condition.
This study also highlights the important role of the EAS program to establish statistically sound data on which to base research into the incidence of conditions such as rib fractures.