Problems of Salmonella sampling.

Modern husbandry practices, regional concentration of the industry, high stocking densities, uniform age-distribution of birds and continuous feeding promote the spread of poultry diseases. Moreover, the immature state of the intestinal microflora or disturbance of the developing flora by antibiotics increases susceptibility of chicks to salmonellas. If an estimate of the number of salmonella-positive birds in a flock is needed, then the required number of samples can be assessed by using the binomial distribution function. Whenever a qualitative result is sufficient, the samples can be pooled or the flock litter can be sampled using an 'overshoe method', which is a novel, low-cost and rapid technique. An optimal pooling factor can be assessed at low prevalence levels (less than 10%). Serological methods will only detect the presence of antibodies to invasive strains of Salmonella. The sampling interval depends on the strategy of the Salmonella Control Programme. Breeder flocks should be sampled more frequently than meat flocks and laying flocks. The new salmonella standard, ISO 6579-1990, is applicable in the poultry industry. When bacterial numbers are likely to be low, or the organisms in a stressed condition, a pre-enrichment step should be included. In the case of faecal samples, however, pre-enrichment should be omitted. A whole carcass rinsing and massaging method is preferred for the examination of finished carcasses.