A multi-level model of data with repeated measures of the effect of lamb diarrhoea on weight

Over a 1-year period, data were collected from three flocks of sheep. A total of 213 lambs were examined routinely from birth to 32 kg (2178 examinations in total). Diarrhoea was seen in lambs of all ages but did not appear to make them systemically ill. The effect of diarrhoea on lamb weight was investigated using MLn, a multi-level modeling program. The data were set at three hierarchical levels: level one, the repeated examinations on each lamb; level two, the lamb; and level three, the litter. Age, the quadratic of age, litter size, sex and farm of origin, all had significant effect on the weight of the lambs. There was also significant random variation in examinations within lambs, between individual lambs and between litters of lambs. There was a reduction in absolute weight of lambs for each week until four weeks after an episode of diarrhoea.