Effects of restricted feeding and sex on the feed to muscle gain ratio of growing pigs

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Abstract. The general aim of the national EFFISCAN project was to investigate the interest of using computed tomography to access new criteria related to body composition and feed efficiency. The specific objective of this study was to compare the lean meat content of carcasses and the muscle composition of weight gain between six purebred pig populations. Abstract. The aim of the study was to compare tissular growth performance between 6 purebred populations, females from three paternal lines, and uncastrated males from 3 maternal lines. The paternal lines and their sample sizes were two Pietrain lines, either homozygous for the N allele (P_NN; n=40) or the n allele (P_nn; n=46) of halothane gene, and a Duroc (Du; n=33) line. The maternal lines and their sample sizes were Large White (LW; n=55), and two Landrace lines (LR; n=30, and LR_M6; n=29). Pigs were raised over 4 batches, distributed in 9 pens of 14 pigs. Feeding was ad libitum in a biphase sequence and consumption (DFI, g/d) was measured individually. Half-carcases were scanned with computed tomography to measure the muscle volume, calculate the Lean Meat Content (LMC, %), and to assess the average daily muscle gain (ADGm, g/d) and the feed to muscle gain ratio (F:Gm, g/g). Least squares means within paternal or maternal lines were compared with a Tukey test. Means with a different superscript letter differ significantly with a P-value less than 5%. The overall means of initial and final body weight were 33 and 123 kg.Regarding paternal lines, LMC was the highest in P_nn (64.2a), the lowest in Du (55.6b) and intermediate in P_NN (61.1c). ADGm was higher in P(757a) than in Du (655b), while ADG was higher in P_NN (1,050a) than in P_nn and Du (1,004b). DFI was the highest in Du (2,723a), the lowest in P_nn (2,438b) and intermediate in P_NN (2,586c). P_nn got the best F:Gm (3.22a), Du the worst (4.18b) and P_NN an intermediate position (3.45c), while P got the best F:G (2.45a) and Du the worst (2.73b). Regarding maternal lines, LMC was the highest in LR_M6 (61.6a), the lowest in LR (57.3b) and intermediate in LW (59.2c). ADGm was higher in LW (757a) than in LR (638b), as well as ADG (1,050a vs 987b). DFI was higher in LW (2,673a) than in LR_M6 (2,433b). LW and LR_M6 got a better F:Gm (3.74a) than LR (4.20b), while there was no significant difference of F:G (2.53). This study showed that F:Gm discriminated breeds better than F:G. Computed tomography seems a suited tool to determine tissue deposition and associated feeding efficiency in test station for breeding purposes.