The effects of dietary protein content and level of feeding on carcass characteristics and organ weights were studied in castrated male Iberian pigs growing from 50 to 100 kg live weight (LW). Animals were offered four diets providing 145, 120, 95 and 70 g ideal crude protein (CP) per kg dry matter (DM) and 13.94, 14.29, 14.56 and 14.83 MJ metabolizable energy (ME) per kg DM, respectively. Three levels of feeding were assayed: 0.60, 0.80 and 0.95 of ad libitum intake. The pigs were slaughtered at 100 kg LW. Daily gain in carcass (carcass gain, g/day) and protein deposition (PD, g/day) in this component attained 76.2% and 78.8% of whole-body average daily gain and PD, respectively. Carcass gain improved with each decrease in dietary CP from 145 up to 120 g/kg DM and then levelled off. A small but significant effect of dietary CP on carcass composition was observed, due to an enhanced fat deposition in pigs fed the lowest protein content diet. Mean values of protein, fat, ash and water contents in the carcass were 101.8, 522.7, 27.6 and 353.7 g/kg respectively. PD in the eviscerated carcass was not affected significantly by dietary protein level but tended to reach a maximum value with the diet that provided 95 g CP per kg DM: 55.7 g/day at the highest feeding level assayed. Carcass energy retention (MJ/day) increased significantly (hairspP < 0.001) with decreasing dietary protein supply and on increasing level of feeding. Raising feed intake resulted in a significant decrease for carcass and a concomitant increase for viscera, as proportions of empty body weight (hairspP < 0.05 and P < 0.001, respectively). Proportional weights of shoulder and ham were not affected either by dietary CP content or feeding level. Proportionate weights of dissectable fat in the shoulder and intermuscular and subcutaneous fat in the ham were not affected by CP content of the diet. In contrast, intermuscular fat content of ham was increased by feeding level (hairspP < 0.05), likely with implications for the quality of the cured meat product.
