Growth performance of growing-finishing pigs fed diets low in protein and energy

Low protein diets facilitate increased backfat in carcass of pigs. Therefore, two experiments with pigs were carried out (one during growing and one during finishing), reducing metabolizable energy (ME) in low protein diets, to determine the effect on performance and carcass characteristics. For the growing trial 32 pigs (16 barrows and 16 gilts; 35.3 +/- 1.5 kg) were used in a randomized complete block design with four treatments (diets) and four replicates. Diets were as follows (% CP and kcal ME kg(-1)): T1) 16.5 and 3265; T2) 12.5 and 3265; T3) 12.5 and 3165; T4) 12.5 and 3065. CP reduction increased feed intake; in gilts feed conversion (FC) was increased and backfat (BF) reduced. Decreasing ME in low protein diets increased intake and lean meat gain (LMG), and in barrows longissimus muscle area (LMA) was increased; in gilts, ME total reduction decreased BE In the finishing trial, 32 pigs (16 barrows and 16 gilts; 56.2 +/- 2.95 kg) were used in a completely randomized design with four treatments (diets) and four replicates; initial body weight was used as a covariable. Diets were as in experiment 1, except for CP (T1=13.8%; T2, T3 and T4=9.8%). Reducing CP caused a decrease in average daily gain (ADG), final weight and LMG, but an increase in FC; in gilts, final weight and ADG were reduced, although FC was increased. Diets with lower ME decreased final weight and ADG, but increased FC; in gilts, final weight, ADG and LMG were reduced, and FC was increased; in barrows there was an increased LMA and LMG. Therefore, low protein diets with lower ME may be used to feed growing pigs; however, in finishing pigs there is a negative effect on carcass characteristics, specially in gilts.