The effects of selection for lean tissue growth on the metabolic and physiological state (i.e., level of maturity) of the pig at birth have been examined on newborns from three breeds that markedly differ with respect to birth weight and postnatal muscle growth potential: a primitive Chinese breed (Meishan, MS), a European breed (Large White, LW), and a composite line (CL) highly selected for high rate of gain. Within each breed, 40 pigs from eight litters were used for whole carcass and tissue sampling, blood sampling, and for a fat tolerance test at 2 h of age. The CL pigs were heavier (P < .001) than the LW and MS pigs at birth but exhibited lower percentages of carcass protein, fat, mobilizable fat, and ash than the MS pigs (P < .05). In addition, MS pigs had larger adipose tissue adipocytes than pigs from the two other breeds (P < .001). Despite their 31% higher RNA capacity in longissimus muscle (higher RNA:protein ratio, P < .05), CL pigs exhibited a lower percentage of muscle protein (P < .05) than did MS pigs. Relative liver weight was higher for LW than for CL pigs (P < .05), which had the lowest percentage of liver phospholipids (P < .01). The CL pigs exhibited lower hematocrit (P < .01), glucose (P < .01), albumin (P < .01), cortisol (P < .01), and thyroxine (P < .05) levels than the MS pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

-An experiment was carried out to evaluate the performance, carcass composition, cutting yields and economic viability of 5 or 10 ppm of ractopamine hydrochloride (RAC) in diets for barrows and gilts from 94 to 130 kg.Sixty commercial hybrid pigs within a gender, were individually kept in pens and assigned a randomized experimental block design, in a 3 × 2 factorial arrangement, with three levels of RAC (0; 5 and 10 ppm) and two sexs (barrows and gilts). There were no RAC × sex interactions for all evaluated parameters. There were significant improvements for the groups of RACtreated on final weight, average daily gain (ADG) and feed:gain (F:G). The RAC, independent from the level (5 or 10 ppm), improved the F:G, but did not influence the average feed intake. The gilts had smaller final weight, smaller average feed intake and better F:G. The supplementation with 10 ppm of RAC provided better carcass yield, better longissimus muscle area and better meat percentage. The pigs supplemented with RAC showed better tenderloin yield, better ham weight and better meat percentage of ham. The gilts had better meat percentage, better back fat thickness, bigger belly flexibility and smaller fat thickness of the belly than barrows. On economic viability, the RAC-treated pigs increased the allowance index, gross earnings and net earnings. Compared to the barrows, gilts showed lower total cost, better allowance index and higher net earnings. The supplementation with 5 ppm of RAC was enough to improve performance, carcass composition and cutting yields in the heavy pigs. Furthermore, 5 or 10 ppm of RAC was economically viable and the heavy gilts were more profitable than heavy barrows.Key Words: additive, carcass modifier, lean meat, nutrition, performance Cloridrato de ractopamina em rações formuladas para suínos machos castrados ou para fêmeas na fase dos 94 aos 130 kg RESUMO -Foi realizado um experimento com o objetivo de avaliar o desempenho, a composição de carcaça e a viabilidade econômica do uso de 5 e 10 ppm de cloridrato de ractopamina (RAC) em rações formuladas para suínos machos castrados ou para fêmeas dos 94 aos 130 kg. Utilizaram-se 60 suínos, distribuídos em delineamento de blocos ao acaso, em arranjo fatorial 3 × 2, composto de três níveis de ractopamina e dois sexos. Não houve interação significativa entre a ractopamina e o sexo para as variáveis analisadas. Observou-se, nos animais que receberam ractopamina, maior peso final, ganho de peso médio diário e conversão alimentar. As fêmeas apresentaram menor peso final, consumo médio diário de ração e conversão alimentar. Para rendimento de carcaça, área de olho-de-lombo e rendimento de carne na carcaça, o nível de 10 ppm foi superior ao controle. A ractopamina, independentemente do nível utilizado, reduziu a espessura de toucinho e melhorou o rendimento de filezinho, pernil e carne no pernil. As fêmeas apresentaram maior rendimento de carne na carcaça, menor espessura de toucinho, maior flexibilidade da barriga e menor espessura de toucinho da barriga. As ...

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RESUMO.O presente trabalho objetivou avaliar o uso de ractopamina em diferentes níveis de inclusão na dieta para suínos em terminação. Foram utilizados 50 suínos híbridos comerciais com peso inicial de 74,08 (1,42) kg, aleatoriamente distribuídos em cinco blocos casualizados. Havia dois animais em cada parcela experimental, macho e fêmea, alimentados com dieta suplementada com ractopamina (0, 5, 10, 15 e 20 ppm) durante 28 dias. Foram avaliados desempenho e características de carcaça dos animais. A ractopamina melhorou o desempenho, espessura de toucinho, profundidade, área de olho de lombo e rendimento de carne na carcaça, porém sem influenciar no consumo de ração, rendimento de cortes e qualidade da barriga. Exceto a dose de 0 ppm, não houve diferença entre as doses de ractopamina utilizadas. O modelo de regressão Linear Response Plateau, aplicado nas variáveis onde houve significância, estimou o ponto ótimo de suplementação deste aditivo entre 4,09 a 5,14 ppm. Houve aumento de 6,09% no índice de bonificação quando foi utilizado o nível de 5 ppm de ractopamina. Conclui-se que a ractopamina é eficaz em melhorar o desempenho e as características de carcaça de suínos em terminação.Palavras-chave: agonista β-adrenérgico, carcaça, desempenho, partidor de nutrientes, qualidade de carne.ABSTRACT. Ractopamine hidrochloride in diets for finishing pigs. The present work was carried out to evaluate different inclusion levels of ractopamine in diets for finishing pigs. Fifty animals with initial weight of 74.08 (1.42) kg selected for high meat deposition were used, randomly allotted in five blocks. Each experimental unit had two animals, barrow and gilt, fed diets with ractopamine (0, 5, 10, 15 and 20 ppm) for 28 days. Growth performance and carcass characteristics were evaluated. Ractopamine improved final weight, average daily gain, feed:gain ratio, backfat thickness, loin depth, loin eye area and lean tissue yield, but did not influence feed intake, cut yields and belly quality. No differences were found among the doses of ractopamine utilized. The optimum level of supplementation of this additive, as estimated by the Linear Response Plateau regression model, was between 4.09 and 5.14 ppm. There was an average increase of 6.09% in the bonus index when ractopamine was used. It was concluded that ractopamine is efficient in increasing the performance and carcass characteristics of finishing pigs.

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