Nutritional effects of feed form , and wheat compared to maize , in the D + and D - chicken lines selected for divergent digestion capacity

Experiment 1 consisted in the genetic selection of two divergent lines D+ and Don the basis of AMEn value measured at 3 weeks of age with birds being fed a wheat diet, using the wheat Rialto cultivar characterised by a high in-vitro viscosity value. Significant difference (3413 J/g DM; P< 0.0001) in AMEn between lines reached 29 % on 4 generation. From the experiment 2 consisting in the test of feed form (mash versus pellet) on feed intake and AMEn value, it could be concluded that difference in feed intake is not a major explanation for the AMEn difference between lines. Experiment 3 conducted on the 4 generation birds showed a strong [line x cereal] interaction on residual feed intake up to 6 weeks of age. Line effect on residual feed intake disappeared on the 8 week. Introduction A previous experiment (Mignon-Grasteau et al., 2004) showed the beginning of a divergent genetic selection of D+ and Dlines, based on the AMEn value of a wheat diet made with a wheat cultivar (Rialto) characterised by a high in vitro viscosity value. The present paper shows the development of this selection up to the 4 generation (experiment 1), the effects of feed form and lines on feed intake and AMEn (experiment 2), and the effects of cereals (wheat from Rialto cultivar versus maize) and lines on residual feed intake from 2 to 9 weeks of age (experiment3). Materials and Methods Experiment 1 followed the genetic selection experiment on digestion capacity previously described for the zero and first generations (Mignon-Grasteau et al., 2004). It consisted in the selection for the next generation birds up to 4 one, with the same methods as those previously used (Mignon-Grasteau et al., 2004). Experiment 2 was conducted with D+ and Dbirds (male and female) from the 3 generation. This experiment consisted in a 2x2 factorial design testing the lines (D+ versus D-) and the feed form (mash versus pellet) on feed intake and AMEn with 18 individual replicates per treatment. Birds were put in individual metal cages at d0 and reared as previously described (Péron et al., 2005). Feed intakes and AMEn values were measured individually for 3 days at 3 wk in ad libitum condition, using acid-insoluble ash as an indigestible marker, as previously described (Péron et al., 2005). Birds were fed a standard starter diet up to 6d. Then, they were fed a 24% protein growing experimental diet based on Rialto wheat (54%), soyabean meal (31%), maize gluten (5%) and rapeseed oil (4.5%). The diet was pelleted (2 mm diameter) with steam. After pelleting, half was ground on 8 mm screen for distribution as mash. The other half was given direct as pellet. Experiment 3 was conducted with D+ and Dbirds from the 4 generation. Effect of lines (D+ versus D-) and cereals (maize versus Rialto wheat) on growth and residual feed intake were tested according to a 2x2 factorial design, with 8 floor pen replicates per treatment and 10 birds (mixed male or female) per pen, from d0 to d63. Residual feed intakes were the residual values of the multiple linear regression giving feed intake as a function of growth and metabolic weight (P) variables, calculated with all the data of the experiment 3 (n = 256). Birds were fed a standard starter diet up to 7d. Then, they were fed ad libitum either maize or Rialto wheat diets from d7 to d63. From d7 to d56, growth diets (12720 J/g; 21.5% crude