cjs-202007-0002 ArticleInAPeriodical 2020 Czech Journal of Animal Science 65 7 247-257 PichlerJosef SchwarzChristiane GierusMartin SchedleKarl Choice feeding in fattening pigs: Effect of diets differing in nutrient density on feeding behaviour and fattening performance The aim of this study was to determine the proportion of feed consumed by pigs when they had the choice to meet their nutrient requirements offering a low (LND) or a high (HND) nutrient dense diet on animal performance and feeding behaviour. In total 120 barrows and gilts were allotted to three dietary treatments (LND, HND and a feed choice group, FC). Diets were calculated to keep a constant ratio of megajoule net energy (MJ NE) to nutrient standardised ileal digestible (SID) lysine, SID methionine and cysteine, SID threonine, SID tryptophan, Ca, available P and Na. Pigs of the feed choice treatment that could choose between LND and HND chose an energy content between 13.3 and 13.6 MJ ME or rather 10.1 and 10.4 MJ NE. The ratio between LND and HND changed during the growing period to a higher percentage of HND (26.2% : 73.8% in the starter, 22.0% : 78.0% in the grower and 20.0% : 80.0% in the finisher phase). No differences between barrows and gilts were detected regarding the selected diet. As a result, similar zootechnical performance data were observed for HND and FC, whereas LND led to a declined (P < 0.05) performance. Regarding the feeding behaviour no differences in the parameters meal size and daily feeder visits between LND and HND (P > 0.1) were observed. However, within the FC treatment more and greater meals were consumed (P < 0.05) at the HND feeder compared to the LND feeder. Pigs of modern genetics still have the ability to cover their nutrient requirements choosing between diets differing in nutrient density without impairing performance. Furthermore, the results give no indication for the necessity of different energy levels in diets for sexed pigs.