The role of nutrition in determining the reproductive performance of sows is still controversial. Much of the dispute arises because in many published experiments there were very few sows in each treatment group. In addition, there have been substantial changes In the husbandry of sows over recent years, and these include the much earlier weaning of the litter at as little as three weeks of age, the breeding of the gilt at a younger age since she reaches 100 kg very much more quickly, and the development of facilities which allow each sow to be treated as an individual. A further change has been in the genotype of the breeding female which means that quite often she enters the reproductive phase of her life carrying very much less adipose tissue than hitherto. The recent development of equipment and techniques to monitor the backfat thickness of sows during life has introduced a new management tool, for which guidelines are readily given, but for which hard experimental evidence is often lacking. The purpose of the coordinated experiment reported here was to attempt to establish critical factors in the history of the sow which put her reproductive performance at particular risk and to evaluate widely recommended practices of Increasing the feed Intake at over the terminal phase of pregnancy, The work was jointly funded by the Department of Agriculture for Scotland and each of the centres.