Causes of variation in pig production are many and not well understood. One of the key issues arises from the spread in pig weights which begins through a kind of competitive process among the pigs beginning well before birth. Competition in the uterus and during lactation results in a sometimes widely spread distribution of potential in pigs by the time they reach weaning. Some common management procedures are implemented beginning at birth to attempt to reduce variation but their outcome is often marginal, while others, such as processing and castration introduce new challenges to subsets of pigs. Pigs of different weights require different environmental temperatures, feed types and other conditions, yet as variation increases, "average" conditions are provided which probably miss the ideal environment for all but a very small number of pigs.
