Social environment in a building is difficult to change because pig flow was determined by the facility's original design. Typically, pigs have been sorted in an attempt to optimize growth rate, make efficient use of available space, ensure pig health, and reduce pen weight variation. The results indicate that the low weight variation in a pen was not maintained through finishing. The social strife in a pen appears to be the greatest between pigs of similar weight because the hierarchy structure of the pen is possibly pushed to increase variation until social order is established. Sorting By Sex Producers have begun sorting pigs by sex to reduce feed costs and better match nutrient supply with requirements.
Barrows grow faster, eat more and have higher nutrient requirements than gilts.
While research has shown split sex feeding does not impact market weight variation in a pen, it does decrease cost of gain. One way to maintain familiarity is to keep litters of pigs together at weaning. However, studies have shown no differences in performance due to the number of pigs coming from the same litter within the same pen. However additional research has shown little improvement in subsequent grow-finish performance. The research referenced indicates the best method to sort or mix a group of pigs at weaning is whatever minimizes labor requirements and maximizes the pig flow through facilities.