The marketing problems associated with natural products are quite different from those of agricultural products, which are produced by many relatively small farms located far from consumer markets. Also, many of these products are produced seasonally. Thus, the distribution channels for most agricultural materials involve many middlemen who buy products from a large number of farmers, collect them in a central location (such as a grain elevator), and store them for shipment throughout the year to processors and exporters. Since there is little difference among the products grown by different farmers, branding is relatively unimportant. There is usually little promotional activity, except for cooperative advertising campaigns funded by trade groups to stimulate primary demand for a product. An example is a promotional campaign to persuade health-conscious adults to drink more milk.