Early Dietary Amino acid Restrictions and Flaxseed Oil Supplementation on the Leanness of Pigs and Quality of Pork: Growth Performance, Serum Metabolites, and Carcass Characteristics
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By taking advantage of compensatory growth, carcass fat can be reduced to satisfy consumer demands and intramuscular fat (IMF) can be increased to enhance organoleptic characteristics pork simultaneously. The beneficial effects of IMF can be enhanced further if its increase can be achieved by omega-3 fatty acids (ω-3 FA) supplementation, which can also reduce lipogenesis. In addition, compensatory growth can improve the overall efficiency of nutrient utilization and economic efficiency, and minimize adverse impacts of pig production on the environment. Therefore, using the concept of compensatory growth and dietary supplementation of flaxseed oil, which is high in the ω-3 FA, to address the pork quality issue can contribute greatly to successful and sustainable pig production. A total of 64 pigs (2 gilts or 2 barrows/pen) 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 x 2 factorial arrangement of treatments on grower-finisher pigs. At 24.7 ± 0.5 kg, pigs were assigned to 4 grower diets with 4 gilt pens and 4 barrow pens/treatment, and switched to finisher-1 diets when they reached 51.2 ± 0.3 kg. Pigs were switched to common finisher-2 diets at 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. The results of growth performance, serum metabolite profile, and carcass traits are reported in this monograph. Pigs fed the AA restricted diets consumed less SID Lys and digestible energy (DE; P < 0.015), and had slightly depressed average daily gain (ADG) compared with non-restricted pigs during the grower phase, but they grew faster (P = 0.042) and utilized feed numerically and SID Lys (P < 0.001) more efficiently during the finisher-1 phase. Dietary AA restrictions had no effect on any of the response criteria during the finisher-2 phase, overall ADG, or carcass traits. The efficiency of overall feed, SID Lys, and DE utilization for body weight (BW) gain (P < 0.004) and SID Lys utilization for fat-free lean gain (P < 0.001) was improved by the AA restrictions. Dietary AA restrictions reduced serum urea N (P < 0.025) at the end of the grower and finisher-1 phases and increased glucose (P = 0.027) at the end of the grower phase, but had no clear effect on other metabolites. Dietary lipids reduced feed intake during the grower (P = 0.007) and finisher-2 (P = 0.064) phases, improved gain:feed (G:F) during all phases and overall (P < 0.047), and improved ADG during the grower (P = 0.003) and finisher-1 (P = 0.066) phases. Belly firmness was reduced (P < 0.001), but there was no other effect of dietary lipids on carcass traits. Dietary lipids increased serum triglycerides at the end of the grower (P = 0.075) and finisher-1 (P = 0.001) phases, but reduced (P = 0.037) urea-N at the end of the finisher-2 phase. Dietary lipids increased serum cholesterol in pigs fed the unrestricted diets but had no effect on pigs fed the AA restricted diets at the end of the finisher-1 phase (AA restrictions x lipids, P = 0.029). The dietary treatment had no effect on ultrasound backfat thickness. In conclusion, as expected, dietary lipids improved G:F but reduced belly firmness. Dietary AA restrictions during the grower and finisher-1 phases had no effect on overall BW gain or carcass traits but improved overall efficiency of AA and DE utilization for BW gain and fat-free lean gain.