Early dietary amino acid restrictions and flaxseed oil supplementation on the leanness of pigs and quality of pork: Growth performance, serum metabolites, carcass characteristics, and physical and sensory characteristics of pork

A total of 64 pigs (Yorkshire) were used to investigate the effect of early dietary amino acid (AA) restrictions [100 or 80% of the 2012 NRC standardized ileal digestible (SID) Lys requirements during the grower and finisher-1 phases] and flaxseed oil supplementation [0 or 3% (+2% poultry fat)] in a 2 × 2 factorial arrangement of treatments on grower-finisher pigs. At 24.7 ± 0.5 kg body weight (BW), pigs were randomly assigned to 4 grower diets with 4 gilt and 4 castrated male pens/treatment and 2 gilts or 2 castrated males/pen, and switched to fnisher-1 diets when they reached 51.2 ± 0.3 kg. Pigs were offered common finisher-2 diets after 80.0 ± 0.4 kg, and those received 0 or 5% lipids during the grower and finisher-1 phases were continued to receive 0 or 5% lipids. Ultrasound backfat measurements and blood samples were collected at the end of the grower, finisher-1, and finisher-2 phases, and pigs were harvested at 110.5 ± 0.5 kg to assess carcass traits and physical and sensory characteristics of pork. During the grower phase, although pigs consumed less feed, SID Lys, and digestible energy (DE; P < 0.015), their average daily BW gain was not really depressed by the dietary AA restrictions. During the finisher-1 phase, however, pigs fed the AA restricted diets had greater BW gain (P = 0.042) and utilized SID Lys more efficiently (P < 0.001) for BW gain than those fed the unrestricted diets. Pigs fed the diets supplemented with lipids had lower feed intake (P = 0.007) but greater BW gain (P =0.03) during the grower phase, and their BW gain:feed (P < 0.045) was improved during the all phases of production. Overall BW gain was not affected by the early dietary AA restrictions, but overall efficiency of feed, SID Lys, or DE utilization for BW gain (P < 0.005) was improved by the AA restrictions. Similarly, the early dietary AA restrictions had no effect on fat-free lean (FFL) gain but increased FFL gain:SID Lys (P<0.001) and tended to increase FFL gain:DE (P = 0.095). Serum urea-N (P < 0.026) at the end of the grower and finisher-1 phases was reduced, and serum glucose (P = 0.027) at the end of the grower phase was increased by the dietary AA restrictions. The dietary lipids tended to increase and increased serum triglycerides at the end of the grower (P = 0.075) and finisher-1 and 2 (P < 0.018) phases, respectively, and reduced urea-N (P = 0.037) at the end of the finisher-2 phase. At the end of the finisher-1 phase, the dietary lipids increased serum cholesterol in pigs fed the unrestricted diet but had no effect on those fed the AA restricted diet (AA restrictions x lipid supplementation, P = 0.029). The dietary AA restrictions tended to reduce the initial tenderness (P < 0.057) and reduced flavor intensity (P = 0.048) of pork slightly. Belly firmness (P < 0.001) was reduced and off-flavor (P = 0.007) was increased slightly by the dietary lipids. There was no effect of dietary treatments on ultrasound backfat. In conclusion, the dietary lipids improved BW gain:feed but reduced belly firmness and increased off-flavor slightly. The dietary AA restrictions had no effect on overall BW gain or FFL gain but improved overall efficiency of AA and DE utilization for BW gain and FFL gain.