Optimal nursery management involves the environment, group formation, feeding, and overall good stockmanship. The lower critical temperature is 26-28°C the first week after weaning due to decreased feed intake and reduces body thermal insulation, but temperature should be gauged more by pig behaviour than the thermostat. If pigs are huddling they will be expending more energy simply trying to keep warm. Once pigs have started eating, temperatures can be lowered at night to save heating costs and stimulate appetite. Poor sanitation can reduce performance by reducing nutrient utilization and stressing the immune system. During mixing some aggression is expected for pigs to settle their new hierarchy, and this appears to have little effect on production. Sorting has generally produced no increase in performance, though pens for sick or particularly poor pigs can still be used. Increases in group size can slightly decrease performance, but may still be justified if it reduces costs in areas like construction or maintenance. More important than group size are the feeder space, feeder coverage, and water access. Performance can also be influenced by birth weight and weaning weight. However, some pigs with the heaviest weight at weaning can be slowest to start eating, and some lighter pigs can be the best performers. Identifying the poor performers and intervening early may be able to help them catch up. Finally, pigs that had been suckling from posterior teats seem to have increased growth compared to those that suckle anterior teats during lactation, but those on posterior teats maintain growth better during the first 4 days of weaning.