A case control study of blowfly strike in lambs

A case control study of the risk factors associated with blowfly strike was conducted on 11 farms in the south west of England. For each case, three control lambs were randomly selected from the remainder of the flock. Samples of blood, faeces and wool were taken from the cases and controls, and measurements of weight, dag score (faecal soiling), fleece length, crimp frequency and tail length were made. Conditional logistic regression was used to examine the univariate and multivariate relationships between the independent variables and the rate of blowfly strike. Case lambs had significantly higher dag scores and lower crimp frequencies than their matched controls, although the association with crimp frequency was confounded by dag score. The relationship between blowfly strike and fleece length was also strongly confounded by dag score. After stratifying by dag score, case lambs had shorter fleeces than their controls. Lambs with blowfly strike had significantly higher levels of blood copper and significantly lower levels of blood urea.