Graded, pre- and post-pelleting additions of whole wheat influences relative gizzard weight, feed conversion efficiency and energy utilisation in broiler chickens

Abstract

The strategy of whole grain feeding is meeting increasing acceptance and various approaches may be adopted in pursuit of this strategy. In this study, a ground wheat-based (600 g/kg) control diet was compared with graded whole wheat additions (7.5, 15.0, 30.0%) incorporated into the ration either pre- or post-pelleting. The seven dietary treatments were offered to eight replicates (6 birds/cage) or a total of 336 male Ross 308 broiler chickens from 7 to 28 days post-hatch. A range of growth performance and nutrient utilisation parameters were determined by standard methods. Pre- pelleting whole grain additions numerically increased relative gizzard weights by up to 13.0% (16.44 versus 14.55 g/kg) at the 30% inclusion. However, post- pelleting additions significantly increased gizzard weights by up to 37.5% (20.01 versus 14.55 g/kg). Overall, whole grain feeding improved FCR (P < 0.03) by 4.35% (1.441 versus 1.506) and at 30%, pre-pelleting whole grain additions significantly improved AME, ME:GE ratios and AMEn but not at lower whole grain additions. In contrast, all three post-pelleting whole grain additions significantly enhanced nutrient utilisation with average improvements of 0.82 MJ in AME (12.89 versus 12.07 MJ/kg), 6.10% in ME:GE ratios (0.743 versus 0.700), 7.36% units in N retention (66.15 versus 58.79%) and 0.68 MJ in AMEn (11.70 versus 11.02 MJ/kg. Interestingly, there was a quadratic relationship between relative gizzard weights and AME (r = 0.650; P < 0.001) where the regression equation was as follows: AME(MJ/kg) = 3.190 + 0.936*gizzard weight(g/kg) – 0.022*(gizzard weight(g/kg))2. In this study the optimal AME of 13.15 MJ/kg, would be generated by a relative gizzard weight of 21.27 g/kg. Thus it appears that AME improvements will plateau at a given gizzard weight increase and further enlargement of the gizzard will not benefit energy utilisation. Further research should be conducted to identify how best to take advantage of whole grain feeding regimes.