The scientific needs of the pig industry change on an ongoing basis, partly because needs are satisfied from time to time, and partly because crises pass. However, there is something more to it than that. Changing need can be characterised as a function of the pig industry's hierarchy of scientific need. The four layers in the hierarchy, in ascending order, can be named thus: Do no harm; Stay in business; Cost less; Charge more.

Do no harm means: don't make people ill (or worse); don't pollute the environment; and don't impair the welfare of pigs in our care. These are basic qualifiers to have the right to produce pigs at all. They tend to be absolute needs where interpretation might be necessary, but where relative positions are not likely to be acceptable (i.e. the pig industry is no worse than the rest). A failure to satisfy these needs makes the pig industry a pariah, and renders all other activity in the industry irrelevant.