With the advent of the stall and tether ban in the UK it is now a requirement to house dry sows in groups throughout their pregnancy which necessitates their being mixed with other sows at some point after service. It is generally recommended that mixing sows during the embryo implantation period should be avoided as this is thought to effect embryo survival rates. The object of this experiment was to demonstrate the aggression that occurs between sows after mixing and determine the effect on reproductive performance when mixing sows at different times during the 42 days post-service.

294 sows were mixed at six different times during early pregnancy: 0 to 7(T1), 8 to 14,(T2) 15 to 21(T3), 22 to 28(T4), 29 to 35(T5) and 36 to 42(T6) days post service. Six groups of sows from six consecutive weeks weanings were served at the first post-weaning oestrus and kept in stable weekly treatment groups until the sixth group was served.