LAMB MORBIDITY IN 3 HOUSED FLOCKS IN SOUTH-WEST ENGLAND DURING 2 LAMBING SEASONS - FARMER VERSUS VETERINARY MONITORING

A 2 year investigation into diseases of early-born, housed lambs was c arried out from 1989 to 1991. The mortality, morbidity and sub-clinica l disease of housed lambs from three flocks were studied. This paper d escribes the collection and analysis of morbidity data. Morbidity was assessed using two techniques. In the first year, a cohort of approxim ately 80 lambs per flock was observed at regular (7 or 14 day) interva ls from birth to slaughter at 10-26 weeks of age. Each lamb was examin ed using a routine clinical examination carried out by two out of thre e members of a trained team of veterinarians. The technique used was t hought to be objective and accurate. However, because there was a smal l proportion (10-12%) of lambs examined there was a lack of informatio n on severely sick lambs and only diseases of prevalence greater than 3.5% had a 95% probability of being identified. This led to a change i n the method of data collection in the second year when the whole floc k of lambs was observed by farmers and lambs which they considered sic k were presented for treatment. Seventeen clinical entities were detec ted in the first year; these were primarily mild conditions. In lambs from Cohorts A, B and C, the mortality rates were 11.8%, 10.5% and 1.3 %, respectively. In the second year, 16 diseases were observed. Lambs presented by the farmers were overtly sick; 15.3% from Flock A and 29. 2% from Flock B died. There were no sick lambs presented by Farmer C. In the second year, sick lambs were observed but the objectivity of th e study was considered to have decreased from the first year. Evidence of this came from the inter-observer bias between farmers. There was a significant difference in the proportion of sick lambs presented by Farmers A and B but there was no significant difference in the proport ion of lambs which subsequently died (1.6% and 1.8% of lambs born in C ohorts A and B, respectively) and which had been presented for treatme nt, suggesting that Farmer A selected less severely sick lambs than Fa rmer B.