Sow performance can be evaluated by weaning-to-oestrus interval, litter size, and farrowing rate. The results vary between countries, but significantly between farms as well. The main cause of differences is management, including handling of the sows and nutrition. Second litter syndrome refers to an increased weaning-to-oestrus interval, but it is often seen as a decreased litter size or farrowing rate in modern sows. The main cause of second litter syndrome is a high amount of weight loss during lactation. As well as decreased performance, sows with the syndrome are often repeat breeders and end up being culled several parities earlier. Preventing weight loss can be done by increasing nutritional intake or reducing milk production, or allowing a recovery period before breeding or during early gestation can increase performance. Annual variations in temperature and light can affect sow performance, with high temperatures or reduced daylight reducing performance. Management strategies should be taken to encourage feed intake, and in the future genetics may be able to play a role. Future considerations for sow performance include the selection for certain heritable reproductive traits, and the effect of shifting to group housing.