2.2. Animals and farms
Females in this study were mainly F1-crossbreds between Large White and Landrace, produced within farm or purchased from breeding companies. Breeding stocks on these farms were originally imported from the Europe or USA. Lactation and gestation diets were formulated by using imported corn and soybean meal. Weaned sows were housed in pens or stalls in a breeding area. Both natural mating and AI were generally practiced. The recommendation was to service females after first estrus postweaning.