The effect of amylose:amylopectin ratio in dietary starch on growth performance and gut morphology in broiler chickens
Starch is the main source of available energy in poultry diets. It is the predominant reserve carbohydrate found in plants and is the main component of the endosperm in cereal grains (EVERS et al., 1974). It is composed of two types of glucose polymers, amylose and amylopectin. Common cereal starches are approximately similar in composition with a range of 0.15 to 0.35 of the total starch being amylose. Variation in the proportion of amylose in the cereal starch can occur for two reasons: Crop growth and husbandry variables can affect the relative proportions of the two polymers. HRUBY (2005) reported a range of 0.17 to 0.29 in amylose content of the starch in 60 maize samples that were entering the commercial animal feed sector. Secondly, the proportion of amylose and amylopectin in the starch is controlled by allelic expression. Cultivars or many cereal types have been developed that are either completely composed of amylopectin (described as ‘waxy’ cultivars) or have a higher amylose content in the starch content. Small amounts of waxy cereal cultivars are grown because they are beneficial for ‘wet-milling’ processes of starch extraction and high amylose cultivars have particular thermal pasting characteristics for human food preparation (GRAYBOSCH, 1998). Although these cultivars are unlikely to be used in any significant proportions in the animal feed sector, some samples may be used that do not meet human food quality characteristics.