The grouping of total number of piglets born was chosen to balance the number of animals in each group. Furthermore, for parity the piglets of parity 1 dams were assigned in 1 group to account for smaller litters and different mortalities from first parity sows (Roehe and Kalm, 2000), and the piglets of parity ≥6 dams were assigned in 1 group because of a significantly greater mortality compared with the other groups (Table 2). The total number of piglets and the mortality
for each level of fixed effects are given in Table 2.