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The nutritive values of twelve samples of different UK wheat cultivars from two different growing years were assessed. A series of chicken feeding experiments were conducted to examine the relationships between chemical composition, grain quality and energy content of the wheat samples and the growth performance of broiler chickens when fed these wheat samples as part of nutritionally complete diets. The efficiency of utilization of apparent metabolisable energy (AMEn) of wheat samples as a source of net energy (NE) was studied. Step-wisc multiple regression analysis indicated that the content of total starch in the wheat samples and the arnylosea: mylopectin ratio in the starch were the main predictors of growth, feed intake and FCR of the broilers. Increasing starch and arnylose content in the wheat cultivar samples gave increasing weight and feed intakes. The Hagberg falling number was also significantly (P < 0.05) positively related to broiler chicken growth and food intakes. Two further experiments indicated that there was a growth response to increasing the amylose: amylopectin ratio, but that the response was specific only to the variations in amylose: amylopectin ratio by using an extracted starch from a high amylose maize cultivar. Variation of the amylose: amylopectin ratio by using different rice cultivars gave no (p > 0.05) differences in broiler growth performance. The influence of different amylose: amylopectin ratios on the physical nature of the starch granule may therefore be more important than their effects in changing the total dietary supply of those starch components. Although the net energy concentration of a wheat sample was related (p < 0.05, r2=0.42) to its determined AME, there was still unexplained variation (about 60%) in the cilicicncy of utilization of AME as a source of NE. A proportion of this variation was, however, explained (p < 0.05, r2=0.40) by differences in the water-extract viscosity of the wheat samples. Different ileal viscosities, due to feeding different wheat cultivars, may result in variation in the amount of intestinal fermentation of nutrients and so altcr the NENE ratio of whcat-based diets. |
