Cattle can tolerate more urea than they can utilise if they are built up to it slowly. About 35g of urea per day is sufficient for substantial production response from breeders weighing around 400kg. 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.