Pelleting of diet ingredients: Diet selection and performance in choice-fed growing pigs

An experiment was completed with individually housed growing pigs to examine whether pigs can compose their optimal diet when allowed a choice of three different pellets. Forty cross-bred pigs (20 castrates and 20 gilts) with an initial live weight of 22.0 ± 2.1 kg were allocated to either a complete control diet (C) or to a choice feed diet (CF) during a 4-week period. The C pigs received a complete feed as one pellet, whereas CF pigs could select their diet out of three pellets being: an energy-rich, protein-rich or premix-rest pellet. The CF pigs were offered their pellets in one feeding trough, which was divided in three compartments. All diets were administered ad libitum. Gilts fed the CF diet selected a higher crude protein (CP) diet than barrows (222 and 193 g/kg DM, respectively), whereas the C pigs, both gilts and castrates, were fed a diet with the same CP content (i.e., 204 g/kg DM; treatment by sex interaction; P<0.05). No other treatment and sex interactions occurred. Pigs fed the C diet had a higher net energy (NE) intake than pigs fed the experimental diet (13.8 MJ/d versus 10.3 MJ/d; P<0.001). The NE intake by gilts tended (P=0.08) to be lower than that by barrows (12.6 MJ/d versus 11.4 MJ/d). Intake of the premix-rest pellet in the CF pigs was very low (15 g/d; 13 g/kg of DM intake). Daily weight gain of the piglets was considerably lower in the CF versus the C pigs (779 g/d versus 541 g/d; P<0.001). Results show that pigs were not able to select a diet to meet their requirements for optimal growth when pelleted diet ingredients were offered free choice in three compartments. Research is required to investigate whether the inability to choose an optimal diet is due to specific organoleptic aspects such as taste, flavour or physical quality of the pellets. When this is clear, our approach can be used to study dietary components, such as secondary compounds or consequences of different feed treatments.