Food ingredient selection by growing and finishing pigs: effects on performance and carcass quality

Abstract

AbstractThe aim was to investigate if selection of a balanced diet by growing and finishing pigs from foods differing in protein content is modified by the intrinsic nutrient and chemical properties of the high protein food ingredient offered. The treatments were as follows: a free-choice was offered between milled barley and either soya-bean meal (SBM) or low-glucosinolate rapeseed meal (RSM) or an equal mixture of SBM and RSM (SBM+RSM). In two further treatments (SBM/RSM and RSM/SBM) the protein supplements were changed when pigs reached 50 kg. These were compared with a control diet (CONT) formulated to provide 13-0 MJ digestible energy (DE) and 10 g lysine per kg and containing barley (680 g/kg), SBM (150 g/kg) and RSM (150 g/kg). A total of 72 pigs weighing about 30 kg were randomly allocated to the treatments in groups of six (three boars and three gilts). Pigs were slaughtered at about 90 kg and the chilled carcasses were assessed by measuring subcutaneous fat depths and cross-sections of the eye-muscle at the last rib. Responses from 30 to 90 kg on treatments CONT, SBM, RSM and SBM+RSM were, for food intake 2·57, 2·37, 2·21 and 247 (s.e. 0·08) kg/day (P < 0·05), for growth rate 0·93, 0·87, 0·70 and 0·82 (s.e. 0·05) kg/day (P < 0·05) and for food conversion 2·77, 2·72, 3·17 and 3·01 (s.e. 0·181) kg food per kg growth (P > 0·05) respectively. The amount of protein supplement selected in the diet from 30 to 90 kg on treatments SBM, RSM and SBM+RSM averaged 524, 495 and 483 (s.e.d. 64·9) g/kg respectively. With SBM this proportion decreased with increasing body weight (P < 0·01; R2 = 0·58). Changing RSM to SBM at 50 kg increased preference for the protein supplement and intake of SBM averaged 983 g/kg from 50 to 90 kg. On the other hand, switching from SBM to RSM increased preference for barley and intake of RSM averaged 572 g/kg. There were no significant differences in carcass quality but treatments RSM and SBM/RSM tended to produce increased fat depths. In conclusion, the use of RSM did not give a satisfactory level of -performance under the restricted free-choice feeding environment of this study. Preference and nutrient intake were adversely modified by RSM possibly due to the undesirable effects of antinutritive factors.