The nutritive value of different wheat varieties for broiler chickens.

The nutritive value of two UK wheat varieties. Dean and Beaver, from three different harvest years was assessed. A series of laboratory analysis and animal feeding experiments were conducted to examine the relationship between chemical composition, grain quality, and starch digestibility characteristics and the productive performance of broiler chickens fed wheat-based diets. Differences were observed in the protein content, Hagberg falling number, hardness, particle size and specific gravity between the wheat varieties. Investigations into the nature of the carbohydrate in each sample revealed significant varietal differences in the amount of free glucose and the ratio of amylose to amylopectin in the endosperm. These results indicated that grains from the variety Dean had a harder endosperm texture, contained more starch packed into larger granules that were composed of proportionally less amylose, and had a lower a-amylase activity than Beaver. Feeding experiments using 7-21 day old broiler chickens confirmed varietal differences in broiler growth characteristics and feeding efficiency that were consistent over harvest years. These differences were not related to the apparent or true metabolisable energy values obtained for the experimental diets or the chemical composition of the wheat samples. A significant relationship between feed conversion ratio and Hagberg falling number and between weight gain and specific gravity of the wheat was attributed to improved starch solublisation and the level of starch filling in the grain respectively, and suggested that the nature of the starch may have influenced the growth of the broiler. A relationship between the free glucose content of the wheat and broiler weight gain and feed intake was deemed to be a reflection of varietal differences in Hagberg falling number, and too small a difference to exert an influence on broiler performance. Significant differences in broiler growth due to wheat variety were found in broilers aged from 7-49 days old, confirming that varietal differences in broiler performance occur throughout a typical commercial growing period. Investigations revealed no significant relationship between digesta viscosity and FCR. The digestibility of the wheat samples was examined in vivo, but was of little value as a measure of digestion differences due to high variation in results between individual animals. Large variety differences were observed, however, using an in vitro method that simulated the digestive processes of monogastric animals. These differences were strongly related to the weight gain, feed intake and FCR of the 7-21 day old broilers when the rate of digestion was less than 34 mg/min/100g, although after this point the relationship was random. Multiple regression analysis revealed that only the true metabolisable energy value significantly improved the linear relationship between the rate of starch digestion and broiler weight gain. The relationship between rate of starch digestion and broiler growth was tested as a possible predictive method of wheat nutritional quality using six variety samples harvested in 1994, fed in pellet or meal form, to 7-21 day old broiler chickens. Significant performance differences between the varieties and diet forms were observed, but there were no significant relationships between performance and rate. The in vitro rate of starch digestion method could not therefore be verified as an accurate predictor of nutritive value of wheat for poultry