Effect of dietary protein source and lysine : DE ratio on growth performance, meat quality, and body composition of growing-finishing pigs

The effects of four protein sources (soybean meal, sunflower meal, pea, and fish meal as the main protein source) and three apparent ileally digestibl e Lys:DE ratios (0.50, 0.43, 0.36 and 0.42, 0.36, 0.30 g Lys/MJ DE for 30 t o 60 kg BW and 60 to 105 kg BW, respectively) in pig diets on growing-finis hing performance, and carcass and meat quality traits were investigated. Ei ght individually housed animals per treatment received the diets from 30 to 105 kg BW at a level of 3.0 times maintenance requirements of energy. The ileal digestibility of protein sources was determined in a previous digesti bility experiment. Protein sources showed no differences in growth performa nce from 30 to 105 kg BW. From 30 to 60 kg BW soybean treatment had lowest performance. The protein sources had no effect on lean meat percentage, liv er weight, or meat quality (intramuscular fat content, pH at 45 min and 24 h after slaughter, drip loss, and meat color measured 24 h and 4 d after sl aughter). The experimental diets formulated on the basis of similar apparen t ileal digestible lysine content resulted in similar body composition rega rdless of the protein source used (P > 0.05). Reducing the Lys:DE ratio fro m 0.50/0.43 to 0.36/0.30 (by about 28%) reduced BW gain by 119 g/d from 30 to 60 kg and by 151 g/d from 60 to 105 kg BW. The gain:feed ratio increased by 82 g/kg in the first phase and by 47 g/kg in the second phase for the h ighest Lys:DE treatment compared with the lowest. Reducing Lys:DE ratio did not modify meat quality traits. A high Lys:DE ratio was associated with a high lean meat percentage. Differences between the medium- and low-Lys:DE g roups were not significant. Lowering the Lys:DE ratio increased (P < 0.05) crude fiat and fatty tissue content and decreased (P < 0.05) protein and mu scle content in the body. Ash content and bone volume were not affected by Lys:DE ratio (P > 0.05). The chemical composition of the carcass can be pre dicted with moderate accuracy (R-2 = 0.39 to 0.58) using volumetric composi tion data of previously frozen carcasses. In conclusion, similar growth per formance, carcass and meat quality, and body composition can be expected if diet formulation is based on the apparent ileally digestible amino acid co ntents of feedstuffs, independent of dietary protein sources. Diminishing L ys:DE ratios reduce growth performance but do not modify meat quality trait s. The chemical composition of the carcass can be predicted with moderate a ccuracy using the volumetric composition of thawed carcasses.