Study design

Sampling was then done in two stages of cluster sampling. In the first stage, purposive sampling of dip-tank areas (Primary sampling units - PSUs) was done within each sub-region. These were selected so that the different sections of the sub-region were sufficiently represented in terms of ecological zone, proximity to commercial farms, proximity to urban areas, remoteness and livestock density. Remoteness was an important criterion for capturing breeds that might be present only in a particular area.

The numbers of dip-tank areas selected within a sub-region depended on the total number of dip-tank areas in that sub-region; in general, the more dip-tank areas (reflecting higher livestock numbers) the larger was the sample.

Taking into consideration cost, human resource and time, it was decided to sample a total of 60 dip-tank areas in each of the four regions, i.e. a total of 240 from the 430 dip-tanks in the SNL, The plan was then to divide them approximately proportionally between the various sub-regions whilst also taking into account livestock density, ecological zone, proximity to commercial farms, etc.

Dip-tank areas were used as a cluster in the sampling frame because they form an important basis of the livestock administrative structure and this is where the majority of the government's livestock departmental field staff is based.