Up to 20g per head per day is sufficient for weaners. However, providing a fixed amount of supplement per head per day is not possible in extensive situations so these intake quantities can only be used as guides. The relative merits of the various commercially available blocks depend on these factors. Many proprietary blocks use salt as both an attractant and an intake regulator. Blocks are a convenient supplement because they usually require little labour input.
Nitrogen sources are no longer inexpensive when compared to phosphorus sources.
However prices of blocks should still be related to their phosphorus content. If it is known that a high phosphorus content is not needed then savings in the cost of blocks can be made. Loose Mixes Loose mixes are homemade supplements that usually have salt as both an attractant and intake regulator. Urea is usually the main source of nitrogen. Loose mixes are generally cheaper than proprietary blocks but need time and labour.