Outdoor sows are subject to a variable climatic environment and to competition within the group for food. High fibre diets, with greater bulk and heat increment, might be beneficial in pregnancy whilst the converse properties might favour high oil diets during lactation.

A 2x2 factorial design compared 2 pregnancy diets, cereal based [C] (122 g/kg NDF, 38 g/kg AEE, 13.0 MJ/kg DE, 157 g/kg CP) or high fibre [F] (222 g/kg NDF, 11.5 MJ/kg DE, 138 g/kg CP), and 2 lactation diets, diet C (as in pregnancy) or high oil [O] (72 g/kg AEE, 14.5 MJ/kg DE, 174 g/kg CP). 231 reproductive cycles of Camborough 12 sows were studied over an 18 month period. Pregnancy diets were fed to paddocks of 8-13 sows at a treatment level providing the same daily intake of DE and protein, adjusted to maintain body condition as appropriate to the time of year.