National animal disease detection system. Evaluation of list frames for disease surveillance of California swine

The authors evaluated existing list frames for disease surveillance by a telephone survey of 50 producers in Tulare county. No single ideal list frame existed, but the list frame of the Statistical Reporting Service, which included only 54% of the surveyed herds and 86% of the breeding swine within the county, had a distribution of herd sizes, production methods and disease histories which closely paralleled those of the surveyed herds. Estimates made later by area frame sampling in the county showed that the master list frame missed a large number of small herds and accounted for only 28% of herds with breeding pigs but over 91% of the swine in the county. In 1983-84, disease problems affected 23 (46.9%) of 49 herds owned by producers involved in the telephone questionnaire. The main diseases reported were diarrhoea 11 (22.4%) herds, pneumonia 11 (22.4%) and atrophic rhinitis 6 (12.2%) herds. Veterinary surgeons visited only 28 of the 50 surveyed herds during 1983-84.