Digestibility and Metabolism of Dietary Nitrogen and Energy in Contemporary, Genetically Lean and Obese Pigs as Estimated by Total Fecal Collection and Acid Insoluble Ash1

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Abstract
Five sets of barrows from contemporary (C), genetically lean (L) and obese (O) phenotypes were used. The C pigs were crossbred Hampshire × Large White. The L and O pigs were crossbred Duroc × Yorkshire from lines selected for either low or high backfat thickness, respectively. The pigs were placed into adjustable cylindrical metabolism cages at 12 wk and again at 19 wk of age for 7-d adjustment and 4-d collection periods. Body weights of C, L and O pigs at 12-wk initial age were 32.9, 25.4 and 18.0 kg, respectively and at 19-wk initial age were 78.6, 55.0 and 39.7 kg, respectively. Pigs in each set consumed their daily feed allowance at the same percentage of their body weights and in two equal feedings. For 12-wk initial age period, daily weight gain (ADG) expressed as percentage of initial body weight was greater (P<.05) for C than for O pigs and was intermediate for L pigs. As determined by the total collection method, the percentage of retained nitrogen (RN) was similar (P>.05) for C and L pigs, but was less (P<.05) for O pigs. Coefficients of apparent metabolizable energy (ME) and N balance-corrected metabolizable energy (MEn) were similar (P>.05) among the three genotypes. The effect of genotypes on coefficients of RN, ME and MEn during the 19-wk initial age period showed the same trend as that during the 12-wk period. However, no difference was noted in ADG among the three genotypes. Apparent digestibilities of nitrogen (DN) and energy (DE) were also estimated by 4 N HCl-insoluble ash method. Genotype had no effect (P>.05) on coefficients of DN and DE for either the 12-wk or 19-wk period. Coefficients of DN and DE obtained by 4 N HCl-insoluble ash and total collection were similar (P>.05) at the 12-wk period, but were higher (P<.01) for the total collection method at the 19-wk period. It is concluded that the leaner C and L pigs retained more of ingested N, but that differences in weight gain and in energy and N retention among C, L and O pigs fed a standard grower diet are not related to digestibilities of dietary N and energy. Further, it is suggested that 4 N HCl-insoluble ash may be used as a natural indicator for estimating apparent nutrient digestibility in pigs, especially at younger ages. Copyright © 1983. American Society of Animal Science. Copyright 1983 by American Society of Animal Science

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