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The main objective of this work was to investigate the effects of feeding Lys-deficient diets on muscle biochemical characteristics, particularly intramuscular fat concentration and fatty acid profile, in a fatty (Iberian) and a conventional pig genotype (Landrace × Large White [LDW]) maintained in identical experimental conditions. Performance and plasma metabolite changes were also monitored. Twenty-eight barrows of 10 kg initial BW, 14 of Iberian and 14 of LDW breed, were randomly assigned to each of 2 experimental diets in a 2 × 2 factorial arrangement (2 breeds × 2 diets). Seven pigs were allocated to each treatment combination. Diets (isonitrogenous and isoenergetic; 200 g CP/kg DM and 14.7 MJ ME) based on barley, corn, corn gluten meal, and soybean meal, with identical composition, except for their Lys content (10.9 g/kg for the diet adequate in Lys and 5.2 g/kg for the diet deficient in Lys), were assayed. Pigs were housed in individual 2 m pens and fed at 85% of ad libitum intake of the Iberian genotype, of greater intake capacity. Daily feed allowance was based on BW individually measured each week. At 25 kg BW, pigs were slaughtered by exsanguination after electrical stun- ning. Blood samples were taken and longissimus dorsi and biceps femoris muscles were rapidly dissected and stored frozen prior to analysis. Performance was reduced in both pig breeds when fed Lys-deficient diets, particularly in LDW pigs (breed × diet interaction, P < 0.05). Intramuscular fat content increased in longissimus dorsi of Iberian (P < 0.05) and in biceps femoris of both pig genotypes (P < 0.01) when fed Lys-deficient diets. Oleic acid increased (P < 0.05) and PUFA acid decreased (P < 0.01) in longissiumus dorsi and biceps femoris of pigs of both genotypes fed Lys-deficient diets. The proportion of oxidative fibers (P < 0.001) and free l-carnitine content (P < 0.05) increased in longissimus dorsi of both pigs types fed Lys-deficient diets. Plasma creatinine was greater in LDW

Thirty entire male Iberian (IB) pigs of 12 kg initial BW were used to study the effects of dietary protein-to-energy ratio on performance, body protein accretion, and tissue composition. Two nutritional regimes were supplied at 3 stages of growth (Phase I, from 12 to 30 kg BW; Phase II, from 30 to 45 kg BW; and Phase III, from 45 to 100 kg BW): the first regime (RefP/E) was formulated to provide optimum protein-to-energy ratios for castrated IB pigs at several stages of growth from 10 to 100 kg BW; the second (IncP/E), for which an overall increase of 2.5 g digestible protein/MJ ME was provided, would allow an increased potential for lean tissue growth presumably well above that expected for the entire male of an obese pig breed. The pigs were surgically castrated at 45 kg BW and slaughtered at about 100 kg BW. In Phases I and II, in which feed was provided ad libitum, no significant differences between dietary treatments in ADG (580 ± 10 and 740 ± 11 g, on average, respectively), G:F (0.475 ± 0.004 and 0.362 ± 0.005, on average, respectively), and gain:ME intake ratio (37.8 ± 0.4 and 26.1 ± 0.4 g/MJ, on average, respectively) were found (P > 0.05). After surgical castration, for the entire fattening period (Phase III), ADFI was fixed and highly restricted. A lower gain:ME intake ratio (14.0 vs. 15.1 g/MJ; P < 0.01) was obtained when the diet with the highest digestible protein:ME ratio was offered (IncP/E). With this regime, body protein accretion significantly improved in the IB boar growing from 12 to 45 kg BW, irrespective of the stage of growth, although the amount of protein accreted was notably enhanced at the later stage (75 vs. 85 g/d in Phase I [P < 0.05] and 110.5 vs. 151 g/d in Phase II [P < 0.001]). However, the efficiency of utilization of dietary N remained unchanged irrespective of the diet fed (P > 0.05). In contrast, in the fattening stage, similar daily rates of N retention (P > 0.05) were found, in spite of the observed differences in digestible