Species-dependent response to the influence of adaptation length during assay for metabolisable energy of cereal grains employing the difference method

Three experiments were conducted to determine the influence of varying lengths of adaptation on metabolisable energy (AME and AMEn) content of maize and barley for broilers, turkeys and laying hens using the difference method. Three hundred and twenty-four Cobb 500 male broiler chicks (Experiment 1), 162 BUT 10 male turkey poults (Experiment 2) or 162 Lohmann brown laying hens (Experiment 3) were offered a nutrient-adequate pre-experimental diet for at least 11 days. The birds were then allocated to 9 dietary treatments (a 3 × 3 factorial arrangement of treatments) with each treatment replicated 6 times. The factors were three diet types (based on wheat-soybean meal (WS), maize-wheat-soybean meal (MWS) or barley-wheat soybean meal (BWS)) and three length of adaptation to dietary treatments (10, 7 or 4 d). The WS was the references diet whereas MWS and BWS were the assay diets. The adaptation period corresponded to 10, 7 or 4 days of feeding experimental diets prior to the end of each experiment. Excreta were collected on the last two days of each experiment. The AME of maize and barley in the assay diets, in each experiment, were calculated using difference method. On all the responses considered, there was no significant diet type × adaptation length interaction in any of the poultry species. Regardless of the poultry species, AME was greater (P < 0.05) for maize compared with barley. The AME (MJ/kg) for maize was 13.5, 13.5 and 13.6 for broilers, turkeys and laying hens, respectively whereas the corresponding AME (MJ/kg) of barley was 12.2, 11.8 and 12.6, respectively. The effect of adaptation length during AME assay was statistically significant in turkeys, tended to be significant in broilers but not significant for laying hens. It was concluded that irrespective of poultry species, the greater overriding factor affecting AME determined by the difference method is the particular feedstuff being assayed. However, length of adaptation to experimental diets during the assay becomes more important in birds with relatively physiologically immature digestive tract.